ssc data summary and data evaluation tables for the

SSC Data Summary and Data Evaluation Tables

for the Thyspunt PSHA project.

K. Coppersmith, K. Hanson, R. Coppersmith, J. Neveling, F. Strasser,

A. Mangongolo, R. Shelembe.

Council of Geoscience

Report Number 2013-0001

Rev. 0

Confidential

The downloaded document is uncontrolled; therefore the user must ensure that it conforms to the

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i

DOCUMENT APPROVAL SHEET

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2013-0001

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COPY No.

SSC Data Summary and Data

Evaluation Tables for the Thyspunt

PSHA project.

DATE OF RELEASE:

8 May 2013

CONFIDENTIAL

REVISION DESCRIPTION OF REVISION DATE MINOR

REVISIONS

APPROVAL

AUTHORS

AUTHOR: AUTHOR:

AUTHOR: AUTHOR: ACCEPTED BY:

K. Coppersmith K. Hanson R. Coppersmith J. Neveling N. Keyser

AUTHOR:

AUTHOR: AUTHOR COMPILED BY: AUTHORISED BY:

F. Strasser A. Mangongolo R. Shelembe M. Havenga G. Graham



ii

Table of Contents

1. Introduction ...................................................................................................................... 1

2. Criteria for Defining Seismic Sources ............................................................................. 2

3. Data Summary Tables ...................................................................................................... 2

4. Data Evaluation Tables ................................................................................................ 326

List of Tables

Table 3.1. Geophyscial Data and Crustal Type and Structure Thyspunt PSHA .......................... 4

Table 3.2. Data Summary Table – Regional Tectonic Setting Thyspunt PSHA ......................... 54

Table 3.3. Data Summary Table - Seismotectonic Models and Seismic Sources (KAR, CK and

NAM), Thyspunt PSHA. ............................................................................................................ 74

Table 3.4. Data Summary Table - Entire SCC Model, Global Assessments, Thyspunt PSHA. 101

Table 3.5. Data Summary Table - Neotectonic Setting, Thyspunt PSHA. ............................... 119

Table 3.6. Data Summary Table - Quaternary, Thyspunt PSHA. ............................................ 173

Table 3.7. Data Summary Table - Regional Structures, Thyspunr PSHA. .............................. 222

Table 3.8. Data Summary Table – Seismicity, Thyspunt PSHA. ............................................. 267

Table 4.1. Data Evaluation Table 6.4. Focal Depth ................................................................ 327

Table 4.2. Data Evaluation Table 6.5. Focal Mechanism Solutions. ....................................... 341

Table 4.3. Data Evaluation Table 6.7. Catalogue Declustering. .............................................. 362

Table 4.4. Data Evaluation Table 6.8. Earthquake Catalogue Completeness. ........................ 371

Table 4.5. Data Evaluation Table 8.2. Global Assessments and Methodologies ..................... 379

Table 4.6. Data Evaluation Table A8.3.1. Extended Continental Crust Source Zone (ECC) ... 389

Table 4.7. Data Evaluation Table 8.3.2 Syntaxis Source Zone (SYN) .................................... 431

Table 4.8. Data_Evaluation_Table_8.3.3-Karoo Source Zone (KAR) ..................................... 444

Table 4.9. Data_Evaluation_Table_8.3.4-Cedarville-Koffiefontein Source Zone (CK) ............ 448

Table 4.10. Data_Evaluation_Table_8.3.5-Namaqua Source Zone (NAM) ............................. 454

Table 4.11. Data Evaluation Table 8.4.1. Kango Fault Source (KNG) .................................... 458

Table 4.12. Data Evaluation Table 8.4.2. Agulhas Fracture Zone Fault Source (AFZ) ............ 475

Table 4.13. Data Evaluation Table 8.4.3. Gamtoos Fault Source (GAM) ................................ 483

Table 4.14. Data EvaluationTable 8.4.4. Plettenberg Fault Source (PLET) ............................ 491

Table 4.15. Data Evaluation Table 8.4.5. Worcester Fault Source (WOR) .............................. 497



1

1. Introduction

As defined in NUREG-2117 (USNRC, 2012), the goal of a SSHAC process is the following:

“The fundamental goal of a SSHAC process is to properly carry out and completely document

the activities of evaluation and integration, defined as:

Evaluation: The consideration of the complete set of data, models, and methods proposed

by the larger technical community that are relevant to the hazard analysis.

Integration: Representing the centre, body, and range of technically defensible

interpretations in light of the evaluation process (i.e., informed by the assessment of existing

data, models, and methods).”

Following this paradigm, the activities of the SSC began the evaluation process by identifying

hazard-significant SSC issues, identifying available data, and augmenting the available

database by gathering new data as part of the geological investigations (GI studies). This

process was enhanced by the activities associated with Workshop #1 during which the results

of hazard sensitivity analyses were presented as a means of identifying hazard-significant SSC

issues, and by the presentations by numerous resource experts of the wide range of geologic,

seismicity, and geophysical data that were available for potential use by the TI Team.

With knowledge of the hazard-significant issues, the TI Team then embarked on the process of

data compilation that marks the evaluation part of a SSHAC process. As defined in NUREG-

2117, the evaluation process consists of a consideration of the data, models, and methods that

have been developed by the larger technical community. Most of the data that are included in

the project database consist of reports and professional publications that relate to seismic

source characteristics both locally, regionally, and by analogy to other parts of the world. To

organise the data topically, an outline of topics and subtopics was developed into which all SSC

data could then be assigned. In this way, members of the team were able to search the

database according to topic and to easily see what data were included for any particular topic.

An important part of the data evaluation process is the documentation of the data that were

considered by the TI Team during the course of the study. For the SSC model, this

documentation is accomplished in three ways: Data Summary tables, Data Evaluation tables,

and in the PSHA project report. This report includes the data tables, which are also appended

to the PSHA report. The tables are organised according to the criteria for defining seismic

sources defined by the SSC TI Team, so these criteria are discussed first below. That is

followed by a description of what is included in the Data Summary and Data Evaluation tables.



2

2. Criteria for Defining Seismic Sources

The seismic source characterisation process for the Thyspunt PSHA began with the

identification of criteria that would be used by the TI Team to define seismic sources.

These criteria were identified based on due consideration of the SCR tectonic regime,

the types of seismic sources that might be present (e.g., fault sources and source

zones), and precedent from recent SSC models developed for similar tectonic

environments and for nuclear facilities. Based on these considerations, unique seismic

sources are defined to account for distinct differences in the following criteria:

1. Earthquake recurrence rate

2. Maximum earthquake magnitude (Mmax)

3. Expected future earthquake characteristics (e.g., style of faulting, rupture

orientation, seismogenic thickness)

4. Probability that a fault is seismogenic

By “differences,” it is meant that a given potential seismic source would differ

significantly in one or more of these criteria from its neighbour such that identifying a

unique seismic source is justified.

3. Data Summary Tables

Data Summary tables are developed for all data sources considered by the TI Team and

include the following information:

• Author

• Title

• Year

• Description and relevance to SSC

• Indication of whether the data are relied upon in the SSC model or not

• Discussion of potential data use

• GIS code

• Originator

The description of the potential relevance to SSC is important because it provides the reader an

indication of exactly what aspects of the paper might relate to SSC technical issues. The very

nature of the seismic source characterisation activity and the models and parameters that

comprise an SSC model are multidisciplinary and involve a wide range of potential data sources.

Thus, it is not unusual for a particular journal article on, say, the regional geologic setting to not

contain much information that is pertinent to SSC. Likewise, some papers are based on data

that are of poor quality or that have been superseded by subsequent studies. In these cases,



3

the potential relevance to SSC would be included in the table to document the fact that the data

were considered, but the answer to whether the data were relied upon for the SSC model would

be “no.” In those cases where the data were relied upon, a data evaluation table was developed,

as described below. A “discussion of potential data use” in the data summary table provides the

data evaluator a location to provide his/her perceptions of the aspects of the data that might be

useful to developing the SSC model, as well as other observations that may be relevant (e.g.,

quality and vintage of the data, limitations and uncertainties in the data).

The downloaded document is uncontrolled; therefore the user must ensure that it conforms to the authorised database version

4

Table 3.1. Geophyscial Data and Crustal Type and Structure Thyspunt PSHA

Author Titlei Year

i Description and Relevance to SSC

Is the data

used in the SSC model?

(yes, no) Discussion of Potential Data Use GIS Code Originator

Heat Flow

Hartnady & Jones Geothermal studies of the Table

Mountain Group aquifer systems.

2007 Ground water temperature is used as a tracer of

hydrogeological processes and a means for testing conceptual

groundwater-flow models.

No JN

Jones Heat flow anomaly in Lesotho:

Implication for the southern

boundary of the Kaapvaal craton.

1992 Heat flow studies in southern Africa reveal a pattern of low

heat flow in Archean cratons compared with Proterozoic mobile

belts that provides grounds for modelling in which cratons have

lower mantle heat flux and greater lithospheric thickness.

New data from Lesotho provide insights into the nature of the

boundary between the Kaapvaal craton and the Natal belt.

Measurements were made in twelve boreholes penetrating

Karoo basalts and sediments in north Lesotho and adjacent

South Africa. The holes form a 90-km-long traverse from

Clareris to Katse just north of the craton boundary (Figure 1).

Traverse show an increase of heat flow from typically cratonic

values of about 45 mW m-2 in the north to about 80 mW m·2

where the craton abuts on the Natal belt in the south. The

change occurs within 30 km.

No JN

Jones A review of heat flow in southern

Africa and the thermal structure of

the lithosphere.

1998 This is a review of about 60 years of heat flow research,

supplemented with unpublished results.

The quality of the data is variable and although all tectonic

provinces is included, the southern part of the NMMB and the

CFB is poorly covered.

In general the Kaapvaal Province and adjacent Archaean

terrains show lower heat flow than the surrounding Proterozoic

mobile belts.

No JN

Nyblade et al. Heat flow in East and southern

Africa.

1990 We report 26 new heat flow and 13 radiogenic heat production

measurements from Zimbabwe, Zambia and Tanzania,

together with details and some revisions of 18 previous heat

flow measurements by other investigators from Kenya and

Tanzania. These measurements come from Archean cratons,

Proterozoic mobile belts, and Mesozoic and Cenozoic rifts.

No JN


5

Author Titlei Year


Is the data



Gravity and Magnetic Data

Beattie, J.C Report of a magnetic survey of

South Africa

1909 First report of a positive magnetic anomaly in the interior of the

Western and Eastern Cape provinces.

Yes Provide background information on the source zones. JN

Branch et al.

(Branch T., Ritter O.,

Weckmann U.,

Sachsenhofer R.F. and

Schilling F.)

The Whitehill Formation - a high

conductivity marker horizon in the

Karoo Basin.

2007 Magnetotelluric (MT) data were acquired along three profiles

across the Karoo Basin in South Africa. The entire Karoo Basin

and its sedimentary sequences are intersected by a number of

deep boreholes, which were drilled during exploration for coal,

oil and uranium. One of the most consistent and prominent

features in the electrical conductivity images is a shallow,

regionally continuous, sub-horizontal band of high conductivity

that seems to correlate with the Whitehill Formation.

To study physical properties and the maturity of the carbon

present in the Whitehill Formation, impedance spectroscopy

and vitrinite reflectance were applied to core. samples from the

SA1/66 borehole, taken from this formation at a depth range

between 2750 m and 2800 m.

It is plausible that the sub-horizontal conductivity anomaly in

the MT model is at least partly caused by the transgressive,

fine-grained, carbon-rich sequences of the Whitehill Formation.

However, the lower Prince Alfred Formation with similarly

gradational composition changes, especially regarding carbon

content (Cole and McLachlan, 1994), cannot be excluded as

an additional contributor. Constrained inversions of the MT

data show that the high conductivity layer associated with the

Whitehill Formation must be horizontally continuous.

No. JN

Cole & Cole Geophysical interpretation of the

marine magnetic data collected in

the offshore site are (8 km radius)

of Thyspunt.

2008 Marine magnetic data collected in the site vicinity of Thyspunt

shows the offshore continuation of magnetic material within the

Cape Supergroup.

The marine magnetic data shows the offshore continuation of

magnetic units within the Cape Supergroup. In one area two

possible northeast-southwest striking faults were inferred. It is

not readily apparent in the sediments on the detailed multi

beam image of the sea floor, but the depth penetration of this

technique is extremely limited compared to that of the

magnetic method. However, the undisturbed nature of the

sediments covering the Cape Supergroup rocks suggest that

the inferred faults have not been active since the deposition of

these sediments. It is also not visible on the airborne magnetic

data in the onshore area covered by Nanaga Formation rocks.

Yes Data suggests that offshore faults have not displayed

any recent movement.

JN

Cole & Naudé Final Report: Airborne Survey of 2007 Report on airborne magnetic surveys were conducted over the

Thyspunt site with the aim of detecting any possible faults that

No, scale JN


6

Author Titlei Year


Is the data



Thyspunt. may be present in the area. Data were collected using a line

spacing of 200 m for an area extending 25 km from the site. In

the site vicinity area (8 km radius around the site) the line

spacing was narrowed to 50 m to facilitate the detection of

narrower features and to conduct a more detailed

interpretation.

Some of the more magnetic lithostratigraphic units such as the

Cedarberg and Gydo Formations are responsible for prominent

northwest-southeast striking anomalies on the data. In addition

to this a large number of linear features that have not been

indicated on the geological map of the area became visible.

The four features that were identified from the airborne and

ground geophysical work for further investigation.

too small.

De Beer The relationship between the deep

electrical resistivity structure and

tectonic provinces in Southern

Africa: Part 2: Results obtained by

magnetometer array studies.

1978 A report on the result of two manetic arrays conducted in 1971

and 1972. The first line stretches from the northern boundary

of the CFB to the Northern Cape and the second array was

from Namibia to northern Botswana.

Author reports a conductive belt underneath the southern part

of the Karoo Basin and northern part of the CFB and

speculates that it is connected to a pre-Cape tectonic province.

Yes Discovery of the SCCB is important background

information in source zone characterization.

JN

De Beer et al. Plate tectonic origin for the Cape

Fold Belt?

1974 Use geophysical data to assess the development of the Cape

Fold Belt.

Conclude that although some features remain unexplained, the

geophysical evidence is consistent with the hypothesis that a

continent-continent collision caused the formation of the Cape

Fold Belt.

No JN

De Beer & Gough Conductive structures in

southernmost Africa: a

magnetoemeter array study.

1980 Beattie anomaly may be correlated with the SCCB and

straddles the N margin of the latter

SCCB probably elongated body of dense & electrically

conductive crust, probably serpentinized pal-oceanic

lithosphere.

Yes Provide information on the position of, and

relationship between the Beattie Anomaly and SCCB.

JN

De Beer & Meyer Geophysical characteristics of the

Namaqua-Natal Belt and its

boundaries

1984. Based on gravity, magnetic and geoeletrical data the authors

propose that geophysical signature can be used to delineate

the boundaries of tectonic provinces.

They maintain that the NNMB southern boundary is traced

along a large static magnetic anomaly and the place where a

transition (N to S) from resistive to conductive crust occurs.

The northern boundary is associated with a gravity signature.

Yes Confirmation that the NNMB envelops the SW, S and

SE rims of the Kaapvaal Craton, and is in turn

bounded by the Damara-Gariep-Malmesbury belts.

N edge of the SCCB is probably the S boundary of

the NNMB. The BMA anomaly coincides with this line

and is described as an edge-anomaly.

JN


7

Author Titlei Year


Is the data



Du Plessis Seafloor spreading south of the

Agulhas Fracture zone.

1977 In this paper the authors makes use of bathemetric, gravity and

magnetic data to trace the AFZ and propose a model for the

Agulhas Plateau.

No JN

Du Plessis & Thomas Discussion on the causative bodies

of the Beattie-set of magnetic

anomalies

1991 The Beattie-set anomalies, which are traced from onland to the

coast in the southeastern part of South Africa consists of five

major anomalies (Empangeni, Durban, Amanzimtoti, Beattie

and the Mbashe) that trend in the east-southeast-west-

northwest direction. The termination of the Beattie and Mbashe

in the west (Cape Province) may indicate the border of the

oceanic crust against the continent. Of the five anomalies, the

Mbashe and Beattie are in the KAR zone.

This information is consistent with data from other published

papers.

Yes Background information on the development of the

source zones.

JN

Graham & Hales Surface-ship gravity measurements

in the Agulhas Bank Area, south of

South Africa.

1965 This paper report on the gravity measurements made in the

southern Indian Ocean.

They report that the crustal profile of the Agulhas Bank is

similar to other reported continental shelf profiles, while that of

the Agulhas Plateau is dissimilar to typeical oceanic curst.

Yes Graham & Hales (1965) interpreted refraction and

gravity data along line CC' (Fig. 1). Their model

indicates a layer of sediments with an average

thickness of 5.3 km and a relief of up to 3 km; and a

crust extending to a depth of 30 to 33 km

JN

Goedhart & Cole Nuclear Siting Investigation

Program: Remote sensing

assessment of the length of

aeromagnetic lineament SV1,

Thyspunt.

2007 This report assesses the continuity and length of the SV1

lineament, both in terms of the certainty of the initial

geophysical interpretation of the feature, and its aerial

photographic expression.

The right-lateral nature of the offset is interpreted to be the

result of a syn-folding PermoTriassic compressional joint or

fracture that was reactivated by dextral transtension during

Cretaceous extension, i.e. an old fault. There is no indication of

more recent reactivation.

The conclusion that it is an oblique normal fault, dipping -

70°NW away from the terrace, is therefore based mainly on the

interpretation of the ground geophysical MEDC traverse A, and

the presence of similar, short, normal faults in the general

area.

No JN

Goedhart et al.

A new geodetic station near

Willowmore, to monitor neotectonic

crustal movement over the Cape

Isostatic Anomaly, Cape Fold Belt,

South Africa.

2009. Poster on a geodetic station installed to several kilometres east

of Willowmore to measure crustal movements over the Cape

Isostatic Anomaly.

No. JN


8

Author Titlei Year


Is the data



Goodlad et al. Mesozoic magnetic anomalies in

the Southern Natal Valley

1982 Authors recognise Mesozoic magnetic anomalies in the Natal

Valley in the SW Indian ocean.

Four previously published magnetic traverses 10 reassessed in

conjunction with newly acquired data reveal a Mesozoic

magnetic anomaly lineation pattern (Cape Sequence) within

the southern Natal Valley. Du Plessis recognized magnetic

lineations normal to the coast but did not correlate these with

any published Mesozoic anomaly models1

The reinterpreted profiles (527, 515/518, 519,371/3, 371/8,

Agulhas 2 and 402) are geographically aligned and compared

with the Mesozoic anomaly sequence of Rabinowitz and

LaBrecque in Fig. 2. Inter-profile correlation and

correspondence to the synthetic model is good.

An areal plot of the magnetic traverses (Fig. 3) show the

anomalies to be in sub-parallel alignment with a strike trend

normal to the Agulhas Fracture Zone (defined here by the

Cape Jope Anomaly). Oceanic crust that was created directly

east of the Falkland Plateau in the Georgia Basin should

theoreticallly generate mirror images of Natal Valley magnetic

profiles although these may now be distorted by differing

ambient field declination, inclination and skewness.

Yes The orientation of the Agulhas Falkland Fracture

Zone (AFFZ) constricted the movement of the

Falkland Islands from Africa toward South America.

The AFFZ is revealed by magnetic geophysical data.

The AFFZ is a good feature to be used as the

eastern boundary of the KAR seismic source zone.

Making the AFFZ the eastern boundary of the KAR

zone is supported by geophysical data and

information from other authors (e.g. Watkeys, 2006).

The Agulhas Falkland Fracture Zone can also be

used to delineate the eastern boundary of the

Cedarville-Koffiefontein seismic source zone. Making

the AFFZ the eastern boundary of the CK zone is

substantiated by geophysical data and information

from other authors (e.g. Watkeys, 2006).

JN

Gough et al. A magnetometer array study in

southern Africa

1973 Report the discovery of a major conductive structure under the

Cape Folded Belt and southernmost Karroo

Yes Provide background information used in source zone

characterization.

JN

Hales & Gough Isostatic Anomalies and Crustal

Structure in the Southern Cape

1960 This paper reports on the Cape Isostatic Anomaly, a negative

isostatic anomaly in the Southern Cape in the region between

the escarpment and the sea, approximately 200 km from the

south and east coasts

The authors consider that these negative anomalies to arise

from the compensation of at least 1.6 km topography which

has been removed by erosion over an 80 km wide belt.

They proposed that the maximum stress is situated between

50 and 60 km from the centre line and that failure will occur at

these points. They also compare this line with the fault system

that at this point 22° E.

Yes Provide background information used in source zone

characterization

JN

Pitts et al. Interpretation of magnetic, gravity

and magnetotelluric data across the

Cape fold belt and Karoo Basin.

1992 Magnetic, gravity and magnetotelluric data from north -south

profiles in the southern Cape Province of South Africa are used

to interpret the crustal structure beneath the Palaeozoic Cape

Supergroup and upper Palaeozoic, Mesozoic Karoo Sequence

sediments.

Based on magnetic data the Beattie magnetic anomaly is

Yes Data on the Beattie magnetic anomaly and the

correlation between the northern edge of the

Southern Cape Conductive Belt (SCCB) and the

Beattie magnetic anomaly and southern margin of

the NNMB should be used in defining source zones.

Gravity model shows that the continental crust south

JN


9

Author Titlei Year


Is the data



modelled as a 30 km wide body, located 7 km below surface

and dipping to the south.

There is a close correlation between the northern edge of the

Southern Cape Conductive Belt (SCCB) and the Beattie

magnetic anomaly. Based on magnetotelluric resistivity-depth

models a zone of electrically conductive crust have been

identified that correlates spatially with the body modelled as

the source of the Beattie magnetic anomaly.

Propose the same model for the origin of the Beattie anomaly

and position of the southern edge of the Namaqua belt.

The origin of these features is still enigmatic but it is possible

that the cause is serpentinised oceanic lithospheric material,

but they may also be as a result of mineralised low angle thrust

faults.

The gravity modeling shows that the continental crust south of

the escarpment is overcompensated and that the crust is

composed of zones of marginal gradational density.

of the escarpment is overcompensated – also

important background info for source zone

characterization.

Quesnel et al. Simple models for the Beattie

Magnetic Anomaly in South Africa.

2009 The origin of the approximately 1000 km-long Beattie Magnetic

Anomaly (BMA) in South Africa remains unclear and

contentious. Key issues include the width, depth and

magnetization of its source. In this study, the authors use

uniformly magnetized spheres, prisms and cylinders to provide

the simplest possible models which predict the 1 km-altitude

aeromagnetic measurements along a profile across the BMA.

Magnetic data used to develop models which predict the 1 km-

altitude aeromagnetic measurements along a profile across the

BMA and compare their results with the interpretation of

independent magnetotelluric and seismic experiments along

the same profile.

Geological sources for the BMA are suggested to be located in

the middle crust and may be displaced by a shear zone or a

fault. Authors propose that granulite-facies mid-crustal rocks

within this belt may cause the BMA. The best-fitting model

corresponds to two wide (~80 km) and highly-magnetized

(more than 5 Am−1) sheet-like prisms which are located at

mid-crustal depths (~10–20 km). Other, less-preferred models

showthat thicker bodies with enhanced crustal magnetization

might extend into the lower crust.

Yes Magnetic data used to develop models which predict

the 1 km-altitude aeromagnetic measurements along

a profile across the BMA and compare their results

with the interpretation of independent magnetotelluric

and seismic experiments along the same profile.

Geological sources for the BMA are suggested to be

located in the middle crust and may be displaced by

a shear zone or a fault. Contrary to previous models

suggesting a serpentinized sliver of paleo-oceanic

crust within the Natal–Namaqua Mobile Belt, they

propose that granulite-facies mid-crustal rocks within

this belt may cause the BMA. All used in source zone

characterisation.

JN

Raath & Cole Ground geophysical survey

investigating a feature indentified

during the airborne geophysical

study of the area around Thyspunt.

2007 Two multi-electrode resistivity traverses were conducted

across a fault inferred from the recently conducted airborne

geophysical survey and situated roughly 5.5 km to the

northwest of Thyspunt.

No. JN


10

Author Titlei Year


Is the data



Singh et al. Seismotectonic Models for South

Africa: Synthesis of Geoscientific

Informtaion, Problems, and the

Way Forward.

2009 Study that develops a seismotectonic model for South Africa,

using a catalog of earthquake activity, geological and existing

geophysical data (gravity and magnetic data).

No JN

Smit et al. The gravity survey of the Republic

of South Africa

1962 A report on South African gravity data in two parts gravimeter

observations and a report on isostatic anomalies. The Cape

Isostatic Anomaly is identified as an important anomaly centred

at S33.6° E25.8°. The anomaly is consistent with 80 km wide

root.

Also review the work of earlier workers who postulated that

failure should first occur along the centre line of anomaly and

that at a later stage faults with large throws should develop

parallel to the centre line at a distance of 50 – 60 km from the

centre.

Yes The position and size of the southern Cape gravity

anomaly are important in source zone

characterization.

JN

Stettler et al. Results of a time domain

electromagnetic survey over four

possible fault positions signifying

the landward continuation of the

Cape St Fracis fault, Cape St

Francis and Oyster Bay, Eastern

Cape.

2008 Assess whether Cape St Francis fault extend onshore near

Oyster Bay and Cape St Francis.

The only candidate traverses are HV, T and CSF. Traverses T

and CSF together represent a profile across the anticline. The

central zone is highly resistive and is represented by a solid

rock, mostly probably the Peninsula Fm Quarzite which is

known to underly the sounding positions. On both sides of the

resistive core of the anticline is a conductive unit probably

represented by the Cederburg formation. However on the

northeastern side of the anticline this conductive unit is much

thicker than on the southwestern side and it is suspected that

the thickening of the conductor in the absence of other

geological evidence, points to the presence of the Cape St

Francis fault being present here.

No JN

Stettler et al. Results of a time domain

electromagnetic survey over four

possible fault positions signifying

the landward continuation of the

Cape St Fracis fault, Cape St

Francis and Oyster Bay, Eastern

Cape – ADDENDUM

2008 The reinterpretation of the TDEM results with recent geological

observations made by Goedhart et al (2008) in the vicinity of

the third site (Line CFS) for the potential onshore extension of

the Cape St Francis fault indicates there is an alternative,

probably more correct model which results in the Cape St

Francis fault dying out before reaching the onshore.

The Cederberg Formation, which contains more shale than the

underlying Peninsula Formation quartzite or the overlying

Goudini Formation is considered softer and the duplication of

the Cederberg Formation as shown in Figure 1 would also

explain why the bay between Seal Point and Cape St Francis

is asymmetrically eroded inland, with the bay being eroded

furthest inland nearer to Seal Point, where the Cederberg Fm

is modeled to occur. This asymmetrical erosion was previously

No JN


11

Author Titlei Year


Is the data



ascribed to the presence of a broad shear zone

Talwani & Eldholm Crustal structure of the southern

margin of the African continent:

Results from geophysical

experiments.

1973 Use magnetic and gravity data, together with seismic reflection

data to investigate the southern African continental margin.

Yes Help characterize southern source zone boundary. JN

Tankard et al. Tectonic evolution of the Cape and

Karoo basins of South Africa

2009 Make use of geophysics data (magnetic, gravity and some

seismic data), tougher with surface geology to develop a

present-day basement architecture of South Africa. Based on

this they propose that first-order faults and the rigid blocks of

basement between them controlled the styles of basin

subsidence and late Karoo magmatism.

The Archean Kaapvaal craton consists of eastern and western

blocks, joined along the east-dipping Colesberg–Trompsburg

fault zone, and terminates southward along the Doringberg

fault.

A broad platform of Proterozoic rocks adjoins the Kaapvaal

craton west and south. The Mesoproterozoic Namaqua block is

separated from Paleoproterozoic Bushmanland basement by

the Buffels River shear zone, and from the Kaapvaal craton by

the Hartbees–Doringberg fault zone. Teleseismic data show

that the Doringberg fault separates thinner Kaapvaal with

large-amplitude Moho character from thick Namaqua crust with

a smaller amplitude Moho (James et al., 2003). Based

onmagnetic character, the boundary between the Namaqua

and Natal basement blocks is interpreted as the Hartbees–

Mbotyi fault zone (Fig. 4), an important control of late Karoo

subsidence. The Namaqua block thins southwards as a rifted

margin (Fig. 5) and continues under the Cape fold belt and

continental shelf. Namaqua-type crystalline basement is

inferred from zircon xenocryst ages of 2.0 Ga in the

Vredenburg and Darling granites (Rozendaal et al., 1999;

Eglington, 2006) and 5.6–6.6 km s"1 P-wave velocities in the

offshore basement (Parsiegla et al., 2007). Average

equilibrium heat flows of 64mWm"2 (Nyblade and Robinson,

1994) imply that the lower Namaqua crust has lower-stress

and lower strength than the Kaapvaal.

Yes The structures described and conclusions made

based on geophysical data are used to delineate the

boundary of different source zones.

Tedla et al. A crustal thickness map of Africa

derived from a global gravity field

model using Euler deconvolution.

2011 Develop a new continental scale crustal model for Africa by

modelling the free-air gravity anomaly EIGEN-GL04C, which

was developed from 30 months of GRACE Level 1B data

covering the period from 2003 February to 2005 July, and

surface gravity data from seven different sources.

No JN


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Weckmann et al. Comparison of electrical

conductivity structures and 2D

magnetic modelling along two

profiles crossing the Beattie

Magnetic Anomaly, South Africa.

2007a Two of the Earth’s largest geophysical anomalies, the Beattie

Magnetic Anomaly (BMA) and the Southern Cape Conductive

Belt (SCCB) extend across the southern African continent for

more than 1000 km in an east-west direction.

New two-dimensional (2D) electrical conductivity models along

a profile from Prince Albert to Fraserburg outline a narrow (2

km wide), southward-dipping zone of high electrical

conductivity in the upper crust below the centre of the Beattie

Magnetic Anomaly (BMA).The inversion results by Weckmann

et al. (2007) suggested that the conductivity anomaly below the

maximum of the BMA is too small to explain the observed

SCCB; however, the anomalously high electrical conductivities

of the entire NNMB crust could explain the observations by the

magnetometer array study. In this study we report on a

comparison of both this data with a second magnetotelluric

(MT) experiment across the BMA, conducted along a 75 km

profile centred on Jansenville, 350 km east of the first profile,

and explore if a common source of the BMA and SCCB is

supported by the electrical conductivity results. The new line

resolves a sub-vertical and narrow conductivity anomaly below

the centre of the BMA. At this location the conductor is

reaching deeper to lower crustal levels and is inclined towards

the north.

The location of both anomalies parallel to the assumed tectonic

boundary of the Namaqua Natal Mobile Belt (NNMB) and the

Cape Fold Belt (CFB) provides the basis for an alternative

interpretation in terms of tectonic structures related to the

accretion process. Their model does not account for rock

composition or amount of remnant magnetization, it implies

that a common source for both geophysical anomalies is

unlikely.

Yes Authors confirm the extent of the Beattie Magnetic

Anomaly (BMA) and the Southern Cape Conductive

Belt (SCCB).

Their model counters previous models about the

assumed tectonic boundary of the Namaqua Natal

Mobile Belt (NNMB) and the Cape Fold Belt (CFB),

which impacts on the placement of the boundary

between the ECC and KAR zones.

JN

Weckmann et al. Magnetotelluric measurements

across the Beattie magnetic

anomaly and the Southern Cape

Conductive Belt

2007b South Africa hosts two of Earth’s largest known continental

geophysical anomalies, the Beattie Magnetic Anomaly (BMA)

and the near coincident Southern Cape Conductive Belt

(SCCB), both of which extend for almost 1000 km in an east-

west direction. To resolve structural details of the SCCB, a

high-resolution magnetotelluric study was conducted along a

150-km-long N-S profile across the Karoo Basin in South

Africa.

For the shallow conductivity anomalies, additional information

could be obtained from deep boreholes. Interpretation of the

deeper anomalies is more difficult as geological constraints are

missing. Northern conductors as well as the conductor beneath

the surface trace of the BMA are located at midcrustal levels of

Yes Authors proposal that the NNMB basement extend

below the CFB as far as the southernmost

continental shelf of Africa has important implications

for placement of host zone’s southern margin.

They suggest that the conductivity anomaly below

the maximum of the BMA is too small to explain the

observed SCCB, which has important implications for

characterizing source zones and source zone

boundaries.

JN


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the NNMB and are likely Mesoproterozoic structure.

Existing tectonic reconstructions and geological sections of the

NNMB and the CFB included the BMA as a 20 km broad and

30 km deep reaching tectonic sliver of serpentinized oceanic

crust [Pitts et al., 1992]. However, such a feature is

incompatible with our conductivity image. Serpentinite in

general is only conductive in active regimes when fluids are

released during its formation and thereby lower the resistivity

[Bruhn et al., 2001]; in fossil regimes, free fluids a not likely

retained at midcrustal depths. Alternatively serpentinite

generally contain amounts of disseminated magnetite, exolved

from olivine during serpentinization. The presence of

metamorphic magnetite could explain the magnetic anomalies,

but for a large conductivity anomaly, magnetite would be

required to be interconnected over substantial distances.

However, because the MT method is not sensitive to magnetic

anomalies, it cannot be concluded that the conductivity

anomaly beneath the trace of the BMA is also the source of the

magnetic anomaly. We believe, it is much more consistent with

other findings in similar settings to attribute the high

conductivities to crustal-scale shear zones. The conductivity

anomaly below the maximum of the BMA is too small to

explain the observed SCCB.

Based on this work the authors propose that the NNMB

basement may extend below the CFB as far as the

southernmost continental shelf of Africa. Their model does not

account for rock composition or amount of remnant

magnetization, it implies that a common source for both

geophysical anomalies is unlikely.

JN

Seismic Refraction and Reflection

Adams & Nyblade Shear wave velocity structure of the

southern African upper mantle with

implications for the uplift of

southern Africa

2011 Broad-band seismic data from the southern African seismic

experiment and the AfricaArray network are used to investigate

the seismic velocity structure of the upper mantle beneath

southern Africa, and in particular beneath the Kaapvaal Craton.

They found phase velocities for the Kaapvaal Craton and

surrounding mobile belts that are comparable to those reported

by previous studies, and we find little evidence for variation

from east to west across the Namaqua–Natal Belt, a region not

well imaged in previous studies. A high-velocity upper-mantle

lid is found beneath the Kaapvaal Craton and most of southern

Africa.

No JN


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Bate & Malan Tectonostratigraphic evolution of

the Algoa, Gamtoos and Pletmos

Basins, offshore South Africa

1992 This paper provides information on the basin framework and

tectonic setting of the Algoa, Gamtoos and Pletmos Basins, the

eastern sub-basins of the OuteniquaBasin (Fig.1). These

Mesozoic half grabens, with areas of respectively 8200km,

5000km and 12500km are filled with up to 10km of synrift and

4 km of postrift sediments. It is largely based on offshore

seismic data. collected from the offshore Algoa,

Gamtoos and Pletmos basins and summarizes the

evolution of these offshore Mesozoic basins.

Yes This paper summarizes the evolution of the offshore

Mesozoic basins. Basins developed following

reactivation of Late Precambrian and Palaeozoic

structures as the result of extension associated with

the Jurassic break-up of Gondwana.

Discusses the initiating of normal faulting along pre-

existing thrust faults during the Mesozoic

Seismic profile on Fig. 2 shows Gamtoos Fault dying

out in Tertiary section, overlain by unfaulted upper

unit.

Seismic data suggest that the Gamtoos is a single

discrete fault plane, but it is possible that it is a

segmented fault zone comprising the Gamtoos and

Elandsberg Faults (like what is observed onshore).

JN

Bräuer, B., Ryberg, T.

& Lindeque, A.S.

Shallow seismic velocity structure

of the Karoo Basin,South Africa.

SOUTH AFRICAN JOURNAL OF

GEOLOGY, 110, 439-448

2007. A Near Vertical Reflection (NVR) Seismic profile from Prince

Albert to Slingersfontein across the Karoo Basin of South

Africa. Study derived shallow velocity models of compressional

waves (P) and shear waves (S) to develop shallow

tomographic P- and S-velocity models for the upper 1 to 1.5

km.

The tomographic models compare well with corresponding

lateral variation in the surface geology of the Permian Karoo

Supergroup sedimentary rocks (Dwyka, Ecca and Beaufort

Groups) deformed at the Cape Fold Belt front. The correlation

between the velocity models and outcrops is stronger for the

southernmost 25 km of the NVR seismic profile. Although the

surface geology is more uniform from kilometre 25 to 50, the

velocity models and Vp/Vs ratio suggest continued systematic

lateral variation. Based on this, we infer a sub-surface

continuation of tight folding not seen in outcrops. The S-

velocity model supports this theory, as velocity variations

correlate well with the location of major fold axes in the

regional scale gentle tight folding of the Ecca Group

(Abrahamskraal Formation). In the northern part of the model,

from 50 to 100 km, minimal change in the velocity models

indicate more uniform and undisturbed lithologies.

No, too

shallow.

Used in

support of

Llindeque

and

others in

subseque

nt papers.

JN

Ben-Avraham et al. Early tectonic extension between

the Agulhas Bank and the Falkland

Plateau due to the rotation of the

Lafonia microplate

1993 The paper utilises data collected during offshore

reconnaissance survey in December 1972-January 1973 area

between 22° and 27°E, immediately north of the Agulhas

Fracture Zone, and across the AFZ, east of 28°E, along the

Cape, Transkei and Natal margin. This data includes

approximately 3596 km and 2623 km of 24-fold multichannel

Yes Information may help with source zone and fault

source characterization.

They consider the curved structures exhibited by the

large fault systems to be Middle Jurassic structures

with a left-lateral strike-slip component, being the

result of right-lateral 'drag' along the AFZ between

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seismic reflection profiles (acquired on a 20 km grid) and

shipboard gravity and magnetic data were recorded over most

of the area.

Provide information on position and nature of the Agulhas

Fracture Zone (AFFZ fault source), fault systems bounding the

Pletmos, Gamtoos and Algoa Basins and evolution of the

continental margin.

South American (SAM) and Africa plates, rather than

being an inherited Cape Fold Belt structures.

The Agulhas Fracture Zone bounds the steep

southeastern continental margin of South Africa

Ben-Avraham et al. Structure and Tectonics of the

Agulhas-Falkland Fracture Zone

1997 Paper based on a large number of multichannel seismic

reflection profiles, collected by SOEKOR, that cross the

continental slope of southeastern Africa.

Provide information on the Agulhas Fracture Zone (AFFZ fault

source) and evolution of the continental margin.

Yes The 1,200 km long AFFZ is divided into four distinct

sections: Mallory Trough, Dias Ridge, East London

segment, Durban segments. Each segment differs

from the others in its physiography and in the nature

of the continent-ocean crustal boundary

Dias Marginal Ridge is a sub-cropping ridge that

bounds the Southern Outeniqua Basin along most of

its southern margin and separates it from the

Agulhas Fracture Zone

JN

Broad et al. Geology of the offshore Mesozoic

basins.

2006 An overview of offshore Mesozoic basins, based largely on

seismic data.

Describe South Africa's continental margins to be a direct

consequence of the break-up and separation of the West

Gondwana supercontinent. Supercontinental break-up, initiated

by extensional forces, commenced in the early Mesozoic.

Separation by continental drifting began in the Early

Cretaceous and is still continuing today

Outeniqua Basin is situated of the southern tip of Africa and

bounded by the Columbine-Agulhas Arch to the W, the Port

Alfred Arch to the E and the Diaz Marginal Ridge to the S. It is

comprised of a series of rift subbasins including the

Bredasdorp, Pletmos, Gamtoos and Algoa sub-basins,

separated by fault-bounded basement arches composed of

Ordovician to Devonian metasediments of the Cape

Supergroup. Southern Outeniqua sub-basin is the distal

extension of the northem sub-basins below the 300 m isobath

Algoa sub-basin includes three half-grabens: onshore Sundays

River Trough; on & offshore Uitenhage Trough; offshore Port

Elizabeth Trough. Arcuate trend of the basin-bounding fault

systems is most likely inherited from the structural grain of the

underlying orogenic Cape Fold Belt (De Swardt & McLachlan,

1982). In Fig 1 the E edge of large fault systems coincides

closely with the 200m isobath.

Mesozoic sedimentary fill of the offshore South African rift

basins is subdivided into synrift and drift phases of

Yes. Limited impact, but some of the information may help

with source zone characterization. Detail on different

sub-basins used in characterization of the ECC zone,

and ECC zone southern boundary.

Info on western continental margin help define

western margin of SYN and KAR zones.

The Agulhas Falkland Fracture Zone (AFFZ) is a

transform fault along which the separation of the

Falkland Plateau occurred when Africa separated

from South America. This demarcates the eastern

source boundary of the KAR zone.

JN


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sedimentation: The earliest synrift sediments are fluvial and

lacustrine in origin, and in some areas are associated with

volcanics and volcaniclastics. They are overlain in most basins

by deltaic and shallow-marine sediments. The drift succession

is characterised by deep-marine argillaceous sediments. In the

Outeniqua basin the beginning of the drift phase is marked by

the 14Atl mid-Albian unconformity

South Africa's western continental margin is a "passive"

volcanic margin and encompasses the greater part of the

Orange Basin sensu stricto, as well as a thin, elongate,

sedimentary wedge along the the western flank of the

Columbine-Agulhas basement arch. Rifting in the west coast of

South Africa, structural complexity and fault severity dissipate

in the in-land direction indicating the limit of rifting. Rifting was

propagated from south to north along the western coast of

South Africa. The limit of the evidence of rifting is used to

outline the southern source boundary of the KAR zone.

Brown et al.

(Brown, Benson, Brink,

Doherty, Jollands,

Jungslager, Keenan,

Muntingh & Van Wyk)

Sequence Stratigraphy in Offshore

South African Divergent Basins,

1995. Present some seismic data in investigation on sequence

stratigraphic analysis of the South African offshore Mesozoic

basins, using seismic data collected by Soekor.

Yes Provide information on fault locations and depths. JN

Doherty The seismic expression of the St.

Croix fault plane, offshore Algoa

basin, showing a history of

extension, inversion, compression,

and strike-slip

1992 The study investigates the St Croix Fault in the offshore the

Algoa Basin (fig. 1) using seismic reflection data collected in

1983 and 1986.

The St Croix fault appears to be a thrust fault, reactivated as a

normal fault and later cut by strike-slip faults.

The mechanism for the folding of the St Croix fault is believed

to be left lateral motion along the Uitenhage Fault – a dip-slip

fault with a strike-slip component of about 5 km, which formed

at the end of rifting.

Yes Provide information on style of faulting of an offshore

fault related to the Coega fault which informs models

for future rupture.

JN

Durrheim Seismic reflection and refraction

studies of the deep structure of the

Agulhas Bank

1987 This study use 12 s two-way time seismic reflection profile, 46

km in length, that straddles the Cape Seal Arch on the Agulhas

Bank and collected during 1985, together with data collected

from Graham & Hales (1965), Hales & Nation (1972) and

Harper (1977) to analyse the geology of the Agulhas Bank. It

provides data on crustal thickness, orientation and style of

offshore faults and any regional changes.

The first deep reflection seismic profile in southern Africa was

shot in 1985 on the Agulhas Bank. It was sponsored by

Southern Oil Exploration Ltd. (Soeker). In order to extract the

maximum amount of information from the single deep profile,

Yes Information in this paper is important background

used in source zone characterization, especially

information on crustal thickness and fault strike, dip

and type (used for future rupture characterization).

JN


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the interpretation made extensive use of existing on-shore and

submarine geological mapping, previous seismic refraction and

gravity surveys, and seismic reflection surveys for hydrocarbon

exploration.

In his Figure 2 the position of the Moho (M) is shown at a depth

of 30 km.

Refers to an unpublished study (Harper, 1977) using two-way

time contour maps of Horizon D and C (the unconformities

marking the onset of rifting and the termination of wrench

tectonics respectively) to analyse the strike and dip of faults.

Virtually all the faults are steeply dipping normal faults.

Near the coastline and most distant from the Agulhas Fracture

Zone the dominant fault strike is 87°, which is approximately

Parallel to the structural grain of the Cape Fold Belt. The ratio

of northerly to southerly dipping faults is about unity. As the

AFZ is approached the angle between the AFZ and the

dominant fault strike increases. Within 100 km of the AFZ the

predominant fault strike is 132° (82° to the AFZ.), and twice as

many faults dip to the southwest as to the northeast. This

overlay of extensional block aulting on the simple wrench

pattern is indicative of divergent wrenching (Wilcox 1973).

Du Toit Mesozoic Geology of the Agulhas

Bank, South Africa

1976 Thesis using seismic reflection profiles and deepwater

boreholes. Structural geological evaluation is done by

mapping two key reflector surfaces.

Onshore trace of fault is a segmented normal fault

terminating at the shore near Groot Brakrivier (Plate 1).

Yes Provide information on fault geometry.

JN

Fouch et al. Mantle seismic structure beneath

the Kaapvaal and Zimbabwe

Cratons

2004 They present results of seismic tomography for a broad region

of southern Africa using data from the seismic component of

the Kaapvaal Project, a multinational, multidisciplinary

experiment conducted in the late 1990s. Seismic images

provide clear evidence of mantle structures that mimic the

surface geology across the region and provide important

constraints on subcrustal structure associated with Archean

cratons. Specifically, a thick (~250 to 300km) mantle keel

exists beneath the Kaapvaal craton; a slightly thinner (~225 to

250km) keel exists beneath the Zimbabwe craton and parts of

the Archean Limpopo mobile belt.

No JN

Goedhart Potential onshore and offshore

geological hazards for the Thyspunt

nuclear site, Eastern Cape, South

Africa: A review of the latest

airborne and marine geophysical

2007 Review the airborne, ground, and marine geophysical surveys

conducted by the Council for Geoscience and Fugro SA within

the Thyspunt Site Area and a 25km inland part of the Site

Vicinity Area (40 km radius) to recommend follow-up

Not the

geophysic

al info,

only some

geological

Vertical fault movement along W-E faults may, in

places, result in a sharp offset along the strike of

dipping fold limbs, which, if observed in isolation,

may appear to reflect left-lateral or right-lateral

faulting. An example of this is the NE-SW striking

JN


18

Author Titlei Year


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data and their impact on the

existing geological model for the

Site Vicinity Area

investigations.

data. . family of Paul Sauer transfer faults which appears on

the CGS 1:250 000 scale map in the Kareedouw –

Cambria area, just NW of the 40km Site Vicinity

radius. This NE-SW fabric is pervasive throughout

the region, and in the Thyspunt Site Vicinity and Site

Areas.

Gohl, Uenzelmann-

Neben

The crustal role of the Agulhas

Plateau, SW Indian Ocean:

evidence from seismic profiling.

2001 Results of extensive seismic survey over Agulhas plateau with

the aim of solving the questions about its crustal structure,

origin and role in a plate tectonic reconstruction context.

The reflection data show clear indications of numerous

volcanic extrusion centres with a random distribution, dated to

the Late Cretaceous time.

Authors did not find indications for continental affinity, but

rather a predominantly oceanic origin of the Agulhas Plateau,

similar to that inferred for the Northern Kerguelen and Ontong-

Java plateaus.

No JN

Gohl, Uenzelmann-

Neben & Grobys.

Growth and dispersal of a

southeast African large igneous

province.

2011 Focus south of the AFFZ, on the Mozambique Ridge (MOZR).

Research is based on deep crustal ocean-bottom seismometer

data and a multichannel seismic reflection profile. This info was

then compared with geophysical models of the Agulhas

Plateau (AP). Propose MOZR and AP forms part of a greater S

Far LIP of oceanic crustal origin with excessive volcanic

eruption and magmatic accretion phases.

No JN

Gough et al. A Magnetometer Array Study in

Southern Africa.

1973. An array of 24 three-component magnetometers was operated

in central South Africa during September and October, 1971.

Results from three substorm sequences are presented in this

paper.

The vertical field has a maximum near Beaufort West and the

horizontal field increases southward to a presumed maximum

just south of the array.

The present anomaly is too large to be produced by induction

in a two-dimensional structure, so that two-dimensional model

calculations can at best locate the structure on some

assumption as to the amplifying efrect of current concentration,

constructive interference or some other cause. We believe that

it is wise to leave the analysis with the fact that a major

structure, involving conductivity contrasts of at least two orders

of magnitude, underlies the Cape Folded Belt and probably the

Karroo Basin. Further observations are planned to extend

coverage towards the coast, and quantitative interpretation will

be attempted when the anomaly is more completely known. No

indication has been found of any conductivity contrast

Yes The discovery of a major conductive structure under

the Cape Folded Belt and southernmost Karoo is

important background information used in source

zone characterisation.

JN


19

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associated with the boundary between the Cape-Vaal craton

and the Namaqualand Mobile Belt.

Green & Durrheim A seismic refraction investigation of

the Namaqualand Metamorphic

Complex, South Africa.

1990. The paper report on the results of a seismic refraction

experiment along a 290 km line betweeb Springbok and

Kakemas in the Northern Cape. The NNMB exhibit

intermediate velocity (diofferent from the Kaapvaal Craton, but

similar to the Damara Province. Moho depth is reported at 42

km. No correlation could be established between the seismic

and electrical resistivity models.

No

Green & Hales Seismic refraction measurements in

the southwestern Indian Ocean

1966 Report on offshore seismic refraction data collected over the

Agulhas Bank and Transkei Basin in the Indian Ocean. Note

that unconsolidated sediment package is thick (1.6 – 2km).

No JN

Gurniss et al. Constraining mantle density

structure using geological evidence

of surface uplift rates: The case of

the African Superplume

2000 In this paper the authors explore the hypothesis that southern

Africa is actively being uplifted by a large-scale, positively

buoyant structure within the mid-lower mantle seismic velocity

variations have been resolved in the deep mantle.

No JN

Hales & Nation A Crustal structure profile on the

Agulhas Bank.

Bull Seism Soc America, 62(4),

1029-1051.

1972 Reports results of seismic refraction profile on the SA

continental shelf. Focused on the Agulhas Bank (260km from

shore) and onshore around Cape Infanta. Paper primarily

discusses raw data from different shots. .

Anisotrophy of velocity on upper mantle resulting from

preferred orientation (in the direction of sea-floor spreading

from SE Indian ocean ridge) of olivine crystals.

No JN

Hansen et al. Estimates of crustal and

lithospheric thickness in Sub-

Saharan African from S-wave

receiver functions.

2009 Estimates of crustal and lithospheric thickness beneath ten

permanent seismic stations in southern, central, and eastern

Africa have been obtained from modeling S-wave receiver

functions (SRFs). For eight of the examined stations, the Moho

depth estimates agree well with estimates from previous

studies using P-wave receiver functions (PRFs). For two

stations, TSUM and BGCA, previous PRF estimates are not

available, and our results provide new constraints on the Moho

depth, indicating crustal thicknesses of 35 and 40 km,

respectively. SRFs

No JN

Harvey et al. Structural variations of the crust in

the Southwestern Cape, deduced

from seismic receiver functions.

2001 Report on some of the results of a seismic experiment during

which fifty-five broad-band seismometers were deployed at 82

seismic stations across southern Africa over a two year period.

Over 1500 teleseismic earthquakes generated by natural

Yes Contains information important to source zone

characterization such as:

Important information on crustal thickness variation.

JN


20

Author Titlei Year


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events were recorded, traversing the structure of the crust and

lithosphere from Cape Town in the south to Masvingo,

Zimbabwe in the north. Receiver functions were generated

from seismic traces recorded by seismographs in the

southwestern Cape to estimate the crustal thickness and other

crustal features.

They supports model that Mesoproterozoic oceanic-like crust

obducted along inferred S boundary of NNMB [232L].

The Moho is found at variable depths. Over a distance of some

300km, from Kenhard southward, the Moho increases from

about 45km to ~ 50km. Beneath the northern margin of the

SCCB and the Beattie Anomaly, the Moho starts to dip to the

north. Southward, for 150km beneath the frontal sector of the

eastern branch of the Cape Fold Belt (north of the Kango

Fault), the crust thins to less than 40km. Farther southward

still, for ~50km beneath the central sector of the eastern

branch of the Cape Fold Belt to the (extension of) the

Worcester Fault, the crust thickens again to about 45km. South

of the Worcester fault the crust thins again to less than 30km at

the coast. The general thinning of the Moho beneath the Cape

Fold Belt is counter-intuitive. This suggests that major

extensional faults or décollements zones, associated with the

regional Jurassic-Cretaceous extension, are rooted in the

underlying crust, perhaps focussed along the south dipping

contacts of the SCCB [240L].

Two upper crustal discontinuities at 7-10km and 20km.

Associated with upper & lower contacts crustal block proposed

to = SCCB & Beattie Anomaly. Thinner than proposed by Pitts

et al. 1992 – 10km vs 20km [240R, 241L]. This block is thinner

in west; maybe because its dip steepens to E [240R, 241L].

Beattie stop at W CFB vs SCCB continues to Atlantic coast

[240R]

The source of the Beattie Anomaly becomes subdued west of

stations SA07 and SA04, and disappears as it approaches the

north-south trending Western Branch of the Cape Fold Belt

(Figure 1). In contrast, the SCCB continues as far as the

Atlantic coast (Figure 1), without being significantly affected by

the north-south trending deformational fabrics of the Paleozoic

and Saldanian structures.

This suggest that the Mesoproterozoic basement of the

Namaqua Natal Mobile Belt continues below the Western

branch of the Cape Fold Belt. The western limit of the Beattie

Anomaly may therefore be a result of tectono-sedimentary

burial by relatively shallow Saldanian- and Cape Basin-age

Models for SCCB and Beattie anomalies

Observation that SCCB continues as far as the

Atlantic coast.

Proposal that Namaqua Natal Mobile Belt continues

below the Western branch of the Cape Fold Belt.


21

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sequences.

Saldanian structures. Based on… SCCB continues as far as

the Atlantic coast (Figure 1), without being significantly affected

by the north-south trending deformational fabrics p241

A crustal source is proposed for the conductive rocks, like the

similar trending Beattie anomaly De Beer and Gough (1980)

and de Beer et al. (1974; 1982; 1992) interpreted this source to

be an elongated body of relatively dense and electrically

conductive crust, possibly a partially serpentinised slice of

paleo-oceanic lithosphere which they suggested marked the

southern edge of the Namaqua-Natal Mobile Belt.

Hirsch et al. Crustal structure beneath the

Orange Basin, South Africa

2007 Investigate the offshore Orange Basin using seismic reflection

data and propose a geological model for the basin.

No. JN

Hirsch et al. Deep structure of the western

South African passive margin -

Results of a combined approach of

seismic, gravity and isostatic

investigations.

2008 The passive margin of the South Atlantic shows typical

features of a rifted volcanic continental margin, encompassing

seaward dipping reflectors, continental flood basalts and high-

velocity/density lower crust at the continentocean transition,

probably emplaced during initial seafloor spreading in the Early

Cretaceous.

The Springbok profile offshore western South Africa is a

combined transect of reflection and refraction seismic data.

This paper addresses the analysis of theseismic velocity

structure in combination with gravity modelling and isostatic

modelling to unravel the crustal structure of the passive

continental margin from different perspectives.

The velocity modelling revealed a segmentation of the margin

into three distinct parts of continental, transitional and oceanic

crust.

No JN

James et al. Crustal structure of the Kaapvaal

craton and its significance for early

crustal evolution.

2003 High-quality seismic data obtained from a dense broadband

array near Kimberley, South Africa, exhibit crustal

reverberations of remarkable clarity that provide well-resolved

constraints on the structure of the lowermost crust and Moho.

Receiver function analysis of Moho conversions and crustal

multiples beneath the Kimberley array shows that the crust is

35 km thick with an average Poisson’s ratio of 0.25. The

No JN

Kgaswane et al. Shear wave velocity structure of the

lower crust in southern Africa:

Evidence for compositional

heterogeneity within Archean and

Proterozoic terrains.

2009 The nature of the lower crust across the southern African

shield has been investigated by jointly inverting receiver

functions and Rayleigh wave group velocities for 89 broadband

seismic stations located in Botswana, South Africa and

Zimbabwe.

No JN


22

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Within the reported uncertainties, we find a 1-to-1 correlation

between our Moho depth estimates and those reported by

previous studies [Nguuri et al., 2001; Nguuri, 2004; Nair et al.,

2006]. The primary new observation that we make is that there

is considerable variability in the velocity structure of the lower

part of the crust across southern Africa.

Because southern Africa has not experienced a major

tectonothermal event since the Karoo flood basalt volcanism at

c. 180 Ma, the variability found within the shear wave velocities

at lower crustal depths most likely results from compositional

differences rather than thermal ones.

The lower crust across much of the southern African shield in

both Archaean and Proterozoic terrains has a predominantly

mafic composition, except for the southwest part of the

Kaapvaal Craton and western part of the Zimbabwe Craton,

where the lower crust is intermediate to felsic in composition.

The mafic layer in the lower crust of the BC is likely caused by

a combination of magmatic intrusion and underplating. The

large thickness of high shear wave velocity lower crust found in

the NNB, CZ, and Kheis Province are consistent with typical

‘‘suture’’thickened crust found in Precambrian terrains globally.

Lindeque et al. Deep Crustal Seismic Reflection

Experiment Across the Southern

Karoo Basin, South Africa

2007 A controlled source Near Vertical Reflection (NVR) Seismic

experiment along a ~100 km profile yields the first high quality

seismic image of the crust and Moho across the southern

Karoo Basin in South Africa.

A highly reflective 42 to 45 km thick crust comprising three

distinct layers: the upper, middle, and lower crust that is bound

by a sharp crust-mantle transition at the Moho. A possible thin

fourth lower-most layer straddles the Moho. An upper crust

region of the Phanerozoic-Mesozoic Cape and Karoo

Supergroup sedimentary rocks (annotated in pink, brown,

yellow and red in Figure 9), increases in thickness from ~5 km

in the north to ~10 km in the south. The dipping reflectors near

the surface (annotated in pink) are ~5 km thick in the south

and ~2.5 km thick in the north, interpreted to represent the

Karoo Supergroup.

At the south end of the profile these basal sequences of the

Cape Supergroup dip beneath the steeply overturned younger

quartzites of the same group that define the seismically and

structurally complex tectonic front of the Cape Fold Belt (CFB).

A possible internal décollement occurs above the sub-

horizontal continuous reflector package and separates the

upper Karoo from the lower Karoo-Cape Supergroups. We

interpret this décollement to occur along the carbonaceous

Yes Important information used in characterisation of the

host zone and zone boundaries, including crustal

thickness, mid-crust continuation further south and

proposal that BMA is unlikely to represents a deep

master suture zone.

JN


23

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shale of the Whitehill Formation (Table 1) as is sometimes

observed in the field (e.g. Figure 34, p. 44 in Knütter, 1994),

but details of the thrust structure were not resolved in the

seismic image.

A seismically defined unconformity separates the subhorizontal

continuous Karoo-Cape sediment sequences that truncate

steeper dipping reflectors in a well-defined mid-crustal layer,

which also hosts the BMA (Figure 9). The mid-crustal layer

directly beneath the unconformity at the base of the Cape

Supergroup displays discontinuous zones of strong reflectivity

and a seismic fabric dip, which is distinctly different from the

upper and lower crust. The mid-crustal layer is ~20 km thick in

the vicinity of the BMA and is likely to be a subsurface

continuation of the 1.0 to 2.0 Ga granitoid gneisses of the

Bushmanland sub-province in the 1.2 to 1.0 Ga Namaqua-

Natal Orogenic Belt. The internal seismic fabric of this layer is

interpreted as a tectonic fabric dipping to the north. The

probable source of the BMA appears at 7 to 15 km depth, as a

narrow feature in a ~10 km wide tectonically complex zone

confined to the upper midcrust.

The underlying lower crustal layer is wedge-shaped: ~24 km

thick in the north and decreasing to ~12 km thick beneath the

Cape Fold Belt. This lower crustal layer may represent

granulite-gneisses of the Namaqua sub-province.

Our results of ~43 to 45 km total crustal thickness agree well

with other studies: 42 to 50 km Harvey et al.(2001) over the

Karoo Basin and Kaapvaal craton; 38 to 51 km of Wright et al.

(2003) and 38 to 43 km (Kwadiba et al. 2003) on the southern

part of the Kaapvaal craton. However, in our NVR data, we do

not observe a sharp change in Moho depth at the CFB front as

suggested by Harvey et al. (2001), but image a Moho that dips

gently deeper below the CFB tectonic front. This is probably

due to the much better lateral and vertical resolution of the

NVR seismic image.

The magnetic source of the BMA can be correlated with a

distinctive zone of high seismic reflectivity and appears

confined to a narrow 10 km wide and 7 to 15 km depth region

in the newly defined crystalline layer of mid-crust. Along the

present seismic section, it seems unlikely that the BMA

represents a deep master suture zone that penetrates the

entire crust.

Lindeque et al. Deep crustal profile across the

southern Karoo Basin and Beattie

Magnetic anomaly, South Africa: An

2011 Developed a deep crustal model, by using diverse geological

and geophysical local, as well as regional datasets. Their

analyses are rooted in the IyA-200501 seismic image and a

Yes Geophysical data provide important background

information to define source zone boundary(ies)

JN


24

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integrated interpretation with

tectonic implications

line interpretation [267R] (Lindeque et al., 2007), but also

include:

• a coincident shallow velocity vs model (Bräuer et al., 2007);

• wideangle refraction data and derived tomography models

(Stankiewicz et al., 2007; 2008);

• archive seismic reflection lines in the Karoo Basin from the

1960’s work of Soekor (now the Petroleum Agency of

South Africa, (PASA), 1967a);

• teleseismic receiver function data (Harvey et al., 2001);

• high resolution magnetotelluric data and models

(Weckmann et al., 2007a);

• regional aeromagnetic data (Council for Geoscience,

(CGS), 2000);

• BMA models (e.g. Quesnel et al., 2009);

• existing geological data from surface mapping (CGS,

1979a; b; 1983; 1992); and

• borehole logs (PASA, 1966; 1967b). [p267]

Along the entire length of IyA-200501, the seismic data imaged

reflectors in the mid-crust dipping north at approximately 20

degrees (Figures 3 and 4) [274R]

The Karoo Supergroup, disrupted by low-angle thrust faults

rooted in a zone of local décollements in the lower Ecca

Group, rest paraconformably on a continuous undeformed sub-

horizontal ~1.5 to 10 km thick wedge of the Cape Supergroup

(CSG).

The Cape Supergroup forms a continuous undeformed sub-

horizontal wedge, 10 km thick at the CFB front in the south and

1.5 km thick under the escarpment in the north. It continues

below the escarpment and does not pinch out as previous

geological-based models suggest. However, the Witteberg

Group still pinches out further south before borehole SA-1/66.

In their model, the regional NNMB mid-crust fabric dips to the

north at ~20 degrees (Figure 9). The mid-crust wedge thins to

the north and consists of three units or blocks [280L]

A series of low angle listric thrusts/faults are identified in the

upper crust (Cape Supergroup & Karoo Supergroup). Listric

faults form an important component of the authors’ model. The

northernmost limit of combined low angle thrusting and

significant folding of the Cape Supergroup is restricted to the

Cape Fold Belt front. The low angle faults do not appear to

and characterize source zones, especially that

of the host zone. This includes data on crustal

thickness and also data used to determine

seismogenic thickness.

Confirmation that low angle thrusting and significant

folding of the Cape Supergroup is restricted to the

Cape Fold Belt front.

The seismic reflection image implies that Pan African

Saldanian rocks are not present to the south.

They provide important information to show that it is

unlikely that the BMA is unlikely to represents a deep

master suture zone and that it cannot be used to

delineate the southern boundary of the NNMB.

Confirming that the Cape Supergroup extends north

as far as the escarpment.

Identify a series of low angle listric thrusts/faults in

the upper crust (Cape Supergroup & Karoo

Supergroup).


25

Author Titlei Year


Is the data



penetrate the basement as the Hälbich (1993) model implied

(compare Figures 10a and 10d). [280L]

The seismic reflection image implies that Pan African

Saldanian rocks are not present below the angular

unconformity. Our interpreted extension of the NNMB to the

continental shelf and up to the Agulhas Falkland- Fracture

Zone (AFZZ) as illustrated in Figure 11, is further supported by

the seismic wide-angle refraction work and subsequent

tomography crustal models of Parsiegla et al., (2007; 2009)

and Stankiewicz et al. (2007; 2008). Their data indicate that

the mid- and lower crust beneath the Cape-/Karoo Basin have

similar seismic properties up to the continental boundary

[280R]

Pan-African Saldanian Orogenic Belt restricted to the west

coast of southern Africa only and divided in the Gariep (Ga),

Saldanian (S) and Agulhas-Columbine-Arch (ACA). [283,

Fig.11].

The postulated Pan African suture zone at the BMA does not

exist. Instead, Pan African aged (520 to 650 Ma) outcrops are

limited to the Gariep, Saldanian and the aligned Agulhas-

Columbine Arch units on the West coast (Figure 11). On the

South coast, the granite outcrops at George (latitude 34°S,

longitude 22.5°E) might imply a Saldanian suture farther south,

but not at the CFB front as the previous models assumed

Data do not support earlier models whereby the southernmost

boundary of the NNMB was defined by a deep BMA and the

Southern Cape Conductive Belt, possibly abutting a Pan

African (Neoproterozoic) suture zone beneath the Cape

Supergroup.

BMA and SCCB may be geophysical manifestations of

tectonically(?) disrupted stratabound ore deposits that may

have been further remobilised through metasomatic

processess of late stage hydrothermal fluids during NNMB

orogenesis. This theory is speculative and need to be tested by

deep drilling.

If subduction to the south is postulated, Palaeozoic oceanic

crust and arc systems should be present to the south of the

CFB (Figure 12b; Burke et al., 1977; Winter, 1984) which they

are in a Gondwana [284R]

They propose a model for the CFB-Karoo basin as a wide,

upper crustal thin skinned Jura-type fold belt, formed in

response to continent-continent collision, or suturing south of

the CFB, with subduction to the south. This seems perfectly


26

Author Titlei Year


Is the data



feasible in a larger Gondwana framework (Milani and de Wit,

2008) and as was also suggested for the Sierra de la Ventana

in Argentina (Ramos 1988, 2008)

This is supported by the general conclusion that the crust of

the Namaqua-Natal Metamorphic Belt likely continues below

the Cape Fold Belt front, probably extending as far south as

the continental margin of Africa up to the Agulhas-Falkland

Fracture Zone. [289 L,R]

Lindeque & De Wit Revealing the Beattie Magenetic

Anomaly and the anatomy of the

crust of southernmost Africa:

Geophysics and deep sub-surface

geology where the CFB and Karoo

meet.

(11th SAGA Biennial Meeting)

2009 Present a tectonic model based on a variety of geophysical

datasets acquired along 2 transects.

No, a

more

comprehe

nsive

version is

found in

Lindeque

et al.,

2011.

JN

Malan et al. The structural and stratigraphic

development of the Gamtoos and

Algoa Basins, offshore South Africa

1990 Use some seismic data to characterize the evolution of the

Gamtoos and Algoa basins.

Report displacement of 12 km on the Gamtoos fault and

propose models for the southwards curve of offshore faults.

Early Cretaceous tensional stresses rejuvenated dip-slip and

minor strike-slip movement along the large arcuate basin-

bounding faults resulting in limited downfaulting of the synrift

(hanging wall) sequence. Dip-slip and limited strike-slip

movement of the hanging wall sequence along the curved

Gamtoos Fault. Along the northwest-southeast trending section

of the Gamtoos Fault, simple dip-slip movement combined with

a small degree of rotation produced extensional faulting

synthetic to the basin bounding fault.

Not the

geophysic

al

informatio

n, only

some

geological

data.

Fault geometry

• Report displacement of 12 km on the

Gamtoos fault.

• Three models proposed to explain the S-

wards curvature of major faults.

1. Bending as result of pull-apart

2. Bending as result of dextural deformation

3. Inherited from Cape Fold Belt structures

Early Cretaceous tensional stresses rejuvenated dip-

slip and minor strike-slip movement along the large

arcuate basin-bounding faults resulting in limited

downfaulting of the synrift (hanging wall) sequence.

Dip-slip and limited strike-slip movement of the

hanging wall sequence along the curved Gamtoos

Fault. Along the northwest-southeast trending section

of the Gamtoos Fault, simple dip-slip movement

combined with a small degree of rotation produced

extensional faulting synthetic to the basin bounding

fault.

JN

McMillan et al. Late Mesozoic basins off the south

coast of South Africa

1997 Provide an overview of the development of Mesozoic offshore

basins along the South African south coast, based on seismic

data.

They confirm that pre-Mesozoic basement in the Pletmos

Not the

geophysic

al

informatio

Offset of Tertiary sediments indicates southern end

of Gamtoos Fault may have been active in mid-

Tertiary, but faulting does not extend through entire

section to seafloor (Fig. 17, based on Malan et al.,

JN


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Basin consists mainly of Ordovician-Silurian Table Mountain

Group quartzites belonging to the Palaeozoic Cape

Supergroup.

In the Gamtoos & Algoa Basins the arches separating basins

are composed mostly of the Palaeozoic Cape Supergroup

(mainly Ordovician-Silurian Table Mountain quartzites and

Devonian Bokkeveld slates) which are aligned along the grain

of the Permo-Triassic Cape Fold Belt. Deep drilling offshore

has intersected basement rocks (Table Mountain quartzites)

only on the flanks of the basement arches and on basement

highs.

n, only

some

geological

data.

1990).

South of southward bend of Gamtoos fault, there is

no indication of offset of the Upper Cretaceous 15At1

unconformity and overlying Tertiary sediments

(Profile H-H′, Fig. 18).

Data indicate style of faulting of the Gamtoos faults is

normal

Offshore, the fault is traced to a depth of at least 12

km.

The 6At1 unconformity marks the end of substantial

normal motion on the Plettenberg Fault, confirming

style of faulting and also its location.

The trace of the Worcester fault as shown on

Figure 1 does not extend as far as Mossel Bay.

Nguuri et al. Crustal structure beneath southern

Africa and its implications for the

formation and evolution of the

Kaapvaal and Zimbabwe cratons.

2001 They report on the results of the southern Africa seismic

experiment, utilizing 55 broadband REFTEK/STS2 instruments

deployed at 81 stations between April1997 and July 1999. The

continuously recorded data of the portable experiment were

supplemented by data from three global digital stations in the

region of the array (Figure 1). They processed 35 teleseismic

events. This work revealed significant differences in the nature

of the crust and the crust-mantle boundary between Archean

and post-Archean geologic terranes.

While results are comparatively sparse for the Namaqua-Natal

and Cape Fold belts, measurements of crustal thickness are

typically 40-50 km throughout the Namaqua-Natal belt and

northern Cape Fold belt. Within the Cape Fold belt, the crust

thins to about 30 km near the African coast. Also see Figure 3.

Yes Crustal thickness data may be used to characterize

seismic source zones.

JN

Parsiegla, Gohl &

Uenzelmann-Neben.

Deep crustal structure of the

sheared South African continental

margin: first results of the Agulhas-

Karoo Geoscience Transect

2007 Using seismic refraction and reflection data from the western of

two sub-parallel offshore seismic lines (Sonne cruise SO-182,

Uenzelmann-Neben, 2005). Profile was extended landward by

Stankiewicz et al., 2007

Outeniqua Basin is either underlain by oceanic or highly

stretched continental crust [394R]

Velocity-depth model consists of six layers

Crustal thickness: crust thins to the S.

• Agulhas Bank: 26 – 30 km (400R)

• Southern Outeniqua Basin: from 25 km in N to 22 km

in the S (401L).

Yes Provide info on continental crustal thickness and how

it thins to the south. The observed crustal thickness

(including sediments) along the profile varies from 30

km on the inner continental shelf to 7 km in the

Agulhas Passage. – used in source zone

characterisation.

The transition zone from continental to oceanic crust

is 52 km wide (profile distance 478 to 530 km); a

typical value for sheared margins (Bird, 2001). It is

characterised by a sharp decrease in crustal

thickness from 30 km on the continental side to 7 km

on the oceanic side and by a southeastward increase

in average crustal P-wave velocity

JN


28

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• Beneath Diaz Marginal Ridge (DMR): from 22 km to 19

km (401L)

• AFFZ: Moho incline ~10° (401L)

• Agulhas Passage: 7 km (401R)

Thinning attributed to extension during Valanginian rifting in the

Falkland Plateau (Richards et al., 1996) and Outeniqua Basin

(Dingle et al., 1983).

Concomitant SE increase in average crustal P-wave velocity

(402R)

Continental crust (velocities between 5.6 - 6.3 km/s in the

upper crystalline crust and 6.4 - 6.7 km/s in the lower crust)

located from the Agulhas Bank to AFFZ (model distance 260 to

510 km

Transition zone from continental to oceanic crust 52 km wide

(profile distance 478 to 530 km), which is a typical value for

sheared margins (Bird, 2001). It is characterised by a sharp

decrease in crustal thickness from 30 km on the continental

side to 7 km on the oceanic side (upper crust: 5.7 to 6.6 km/s,

lower crust: 6.7 to 7.1 km/s) a [402R]

Additional thinning may have occurred as a result of the shear

process itself. A ductile (not rigid) crust of African plate were

dragged along the AFFZ and bent before frictional tension

released. Evidence preserved today in the curved strikes of the

bounding faults in the northern Outeniqua Basin (403L)

Propose combined explanation for geometry of fault strikes:

Some inherited zones of weakness, i.e. old faults of the CFB,

re-activated due to extensional forces causing the

development of horst and graben structures. Also, shear

motion between the African and South American plates,

dragged ductile African crust along the AFT resulting in a

bending of existing and newly developed fault structures.[403]

Diaz Marginal Ridge neither a volcanic feature nor a crystalline

basement ridge, but instead may consist of metasediments

[406L].

Parsiegla, Gohl &

Uenzelmann-Neben

The Agulhas Plateau: Structure and

evolution of a large igneous

province.

2008 Using seismic refraction and reflection data from the eastern of

two sub-parallel offshore seismic lines (Sonne cruise SO-182,

Uenzelmann-Neben, 2005). It is 670km long and stretches

from the Outeniqua Basin to the southern Agulhas Plateau

(APlat), crossing Agulhas Passage and AFFZ [336, 337R,

338L]

Big focus of the paper is to determine if Agulhas Plateau

Yes Provide info on Agulhas Plateau that is used as

background in source zone characterization.

JN


29

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has continental or oceanic affinity [336R]. They eventually

conclude that velocity–depth structure of AP typical for over-

thickened oceanic crust observed at oceanic LIPs [341R], But

may have embedded small slivers of continental fragments,

have broken off from earlier conjugate continental crust [343L]

Moho depth ranges from:

• 31 km beneath the continental shelf

• thins from 30 to 12 km in the Agulhas Passage

• Increase from 15 – 22 km at N Agulhas Plateau

• Constant depth of 23 km on average. [341R]

Geophyscis show not continental affinity in APlat [342R]

Crustal thickness ranges from

• 30 km in N part of the profile

• 8–14 km in Agulhas Passage (APas),

• 11–20 km at the N part of the Agulhas Plateau (APlat)

• 20 km in the central part of APlat

Backtrack on previous theory (say it is not clear) that proposed

magmatism of the APlat linked to Mozambique Ridge (Gohl &

Uenzelmann-Neben, 2001). [345L]

They suggest that the southern APMR-NEGR LIP formed as a

result of excessive magmatism caused by the interaction

between the Bouvet hotspot and the triple junction. [345R

Also attribute processes of continental breakup, triple junction

activity, LIP formation and Bouvet hotspot activity to the

mechanism of large-scale, enduring and distributed mantle

upwelling of varying intensity and at different times [346L]

Recognise tripartite structure for AP crust (20km in total)

[348R]

• Volcanic flows which make up the upper part of the crust

• Middle crust continuous and forms sub-vertical zone at

370 km in profile [341R]

• Lower crust – 10km - high velocities

Parsiegla,

Stankiewicz, Gohl,

Ryberg &

Uenzelmann-Neben.

Southern African continental

margin: Dynamic processes of a

transform margin.

2009 The investigation acquired seismic refraction / wide-angle

reflection data along two combined onshore-offshore profiles

across the southern continental margin of SA. [2R] (see

Uenzelmann-Neben, 2005). Parts of these profiles have also

been published by Parsiegla et al. [2007, 2008] and

This paper provides information on crustal thickness

that is critical to delineating the boundaries off the

host source zone. The model on amount of stretching

experienced by the crust in offshore region is

JN


30

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Is the data



Stankiewicz et al. [2007, 2008]. In this paper the onshore

[Stankiewicz et al., 2007] and offshore [Parsiegla et al., 2008]

velocity-depth models are combined in a joint model of the

velocity-depth structure from the Karoo Basin to the Agulhas

Plateau

Recognise 4 crustal types along the E profile

1. Unit 1 (0 to 300 km). Crust 42 km thick on onshore part, 28

km on the shelf. Onset of crustal thinning begins 50 km

inland from the coast. Crustal velocities for stretched

onshore & offshore continental crust suggest Cape

Supergroup underlie the shelf (consistent with drilling –e.g.,

McMillan et al., 1997).

2. Unit 2 (300 –350 km), Moho ascend from 25 – 14 km (over

distance of 50 km). Velocity classifies it as a continent-

ocean transition (COT) zone.

3. Unit 3 (350 – 435 km) crustal thickness in the Agulhas

Passage varies between 6 –10 km

4. Unit 4 (435–890 km) – on Agulhas Plateau crustal

thickness increases to 20 km

Authors assume initial crustal thicknesses before stretching, of

43 km (W profile) and 42 km (E profile) [10R]

Stretching factors increase from north to south along both

profiles (Figure 8). The lowest stretching factors were observed

in the southernmost CFB with average b factors of 1.1–1.2.

Peak b factors occur next to the AFFZ (b = 3.2–3.3). Stretching

factors in the Pletmos and Gamtoos Basins are similar (b =

1.6), while in the Southern Outeniqua Basin b = 1.9. [11R]

The subdivision between the area of the Outeniqua Basin

which experienced one and the area which was affected by

two stretching episodes is marked by a dashed line [12, Fig. 8]

Thus, the clear step in our calculated Outeniqua Basin

stretching factors can be interpreted as reflecting one episode

of extension in the northern subbasins and two episodes in the

wider southern basin. [12L]

From stretching factors (calculated from thickness info), they

infer that Gondwana rifting / break-up / sea-floor spreading (?)

resulted in crustal thinning over the whole basin and up to 50

km inland of coast (Fig 8). Main stress direction in Fig 8 is

perpendicular to AFFZ [12].

Propose that crustal stretching (Jurassic) followed by a 2nd

period of thinning associated with shear along AFFZ (Cret.) [2].

especially important.

According to the velocity-depth structure and the

average velocities of the crystalline crust (Figures 6a

and 6b), the profile can be subdivided into four units

from north to south

1. From 0 to 300 km profile distance, the crust

is about 42 km thick on the onshore part and

about 28 km on the shelf. These thicknesses

are within the normal ranges for unstretched

and stretched continental crust [e.g.,

Christensen and Mooney, 1995]. The onset

of crustal thinning begins 50 km inland from

the coast.

2. The region between 300 and 350 km profile

distance (Figure 6b) is characterized by the

Moho’s ascent from 25 to 14 km over a

distance of 50 km,

3. The crustal thickness in the Agulhas

Passage varies between 6 and 10 km (350 to

435 km profile distance). Although this

thickness is in the normal range for oceanic

crust, the average crustal velocity of 6.04

km/s is at the lower limit of those reported

4. On the Agulhas Plateau (profile distance

435–890 km), the crustal thickness increases

again to an average of 20 km. This

significantly higher average crustal velocity

(6.5 km/s) is due to the Agulhas Plateau’s

~10 km thick high-velocity lower crustal body,

which identifies it as a Large Igneous

Province [Parsiegla et al., 2008].

See section on Calculation of Crustal Stretching

Factors: Thinning of continental crust between

distances 180 and 520 km on the western profile is

considered to be the result of crustal stretching

(Figure 6c). Stretching factors increase from north to

south along both profiles (Figure 8). The lowest

stretching factors were observed in the southernmost

CFB with average ß factors of 1.1–1.2. Peak ß

factors occur next to the AFFZ (ß = 3.2–3.3).

Stretching factors in the Pletmos and Gamtoos

Basins are similar (ß = 1.6), while even higher in the

Southern Outeniqua Basin ß = 1.9.


31

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N limit of 2nd

event’s influence roughly associated with faults

southern margin [observation from Fig 8,].

Also propose models for origin of Diaz Marginal Ridge (directly

N of AFFZ) [14L], Outeniqua & Falkland basins (14R),

continental margin evolution [15-16]

Calculated Outeniqua Basin stretching factors can be

interpreted as reflecting one episode of extension in

the northern subbasins and two episodes in the wider

southern basin.

The shear motion along the Agulhas Falkland

Transform started ~136 Ma and actively forms the

continental margin and caused a second pulse of

crustal stretching in the Outeniqua Basin (see Figure

9).

Paton Influence of crustal heterogeneity

on normal fault dimensions and

evolution: southern South Africa

extensional system.

2006 This study investigates the development of the southern South

African extensional system and makes use of seismic data to

characterize some of the faults, especially offshore faults.

Author recognises a correlation in the trends of the Cape Fold

Belt structural fabric and the Mesozoic extensional faults, and

this is especially evident to the southeast where there is

change in trend from an E–W orientation to a NW–SE trend of

both the structural fabric and the extensional faults

Overall displacement–length dimensions of the extensional

faults were inherited from the underlying compressional faults

Kango, Baviaanskloof and Gamtoos arrays are considered part

of the same fault system that is at least 480 km long. The fault

system, and the arrays that comprise it, are therefore

comparable with the longest fault systems that have been

documented in continental lithosphere

This 480 km-long Mesozoic extensional system comprises a

number of fault arrays that vary in length from 78 to 230 km.

Coupled with displacements of up to 16 km, the fault arrays are

amongst the longest and largest displacement of high angle

normal faults (dips of 45–60°) documented in continental

lithosphere.

Towards the SE the extensional faults change in trend from an

E–W orientation to a NW–SE trend of both the structural fabric

and the extensional fault.

Displacement in the offshore Pletmos and Gamtoos basins are

consistently larger than 12 km. The displacements of the

hanging-wall to footwall cut-offs are estimated to be 13,000 m

and 16,500 m respectively (conservative estimates).

The Kango and Baviaanskloof Fault planes are visible at some

localities and dip at approximately 60° towards the south.

Yes There is no bathymetric expression of the Gamtoos

fault and hence it is considered inactive,.

Fault geometry

The Gamtoos Fault is dips at 42.5°, is 170 km long

and if linked with the Kango and Bavianskloof Faults.

Cross-sectional geometry of the Gamtoos fault plane

demonstrates that the fault is continuous, linear, and

nonsegmented (Fig. 8).

It is a normal fault, based on offset of Tertiary and

older sediments in marine seismic profiles

Interpretation does not show Gamtoos anticline in

hanging wall; possible alternative interpretation of a

more steeply dipping fault is suggested by other

researchers (e.g., Malan et al., 1990).

Indirect information regarding segmentation—No

evidence at the resolution of data of fault

segmentation.

Subdivides the 230 km long Kango Fault (dipping at

60° south) into five discernable segments. The

western end of the fault is near Ladismith, and its

eastern limit is southwest of Willowmore.

Does not call out any active segment, but the active

segment for the Kango Fault cited by others is split

into at least three segments, which are 30, 20, and

20 km long from west to east.

Kango Fault dips at 60° south. Estimates dips on

neighboring Plettenberg and Gamtoos Faults as 65°

and 42.5°, respectively.

The Plettenberg Fault is a normal fault based on

offset of Tertiary and older sediments may come

ashore in Plettenberg Bay and be associated with

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Mesozoic sediments.

Observed minimum length 160 km. 50°–65° planar

dip (Figure 7). Fault imaged to a depth of 13 km.

Evidence for segmentation of P{Lettenberg fault :

Despite change in trend of the fault from WNW–ESE

to N–S orientation, the cross-sectional geometry of

the fault remains the same along the entire length.

Interpolation of the fault plane to form a 3-D surface

produces a fault plane that is a discrete,

approximately continuous, smooth surface without

steps in trend. There is no evidence of abandoned

fault tips in either the hanging wall or footwall, or an

en-echelon configuration, and therefore, the fault

does not comprise a nonlinear fault segment.

Paton et al. Applicability of thin or thick skinned

structural models in a region of

multiple inversion episodes;

southern South Africa

2006 Investigation into the structural models for southern SA and

ustilise seismic data to characterize various offshore faults.

The deformation of the Cape Fold Belt has been attributed to

repeated structural reactivation of a mega-detachment from the

late Proterozoic to the Mesozoic (650±65 Ma).

Their regional scale cross-sections through the Permian-

Triassic Cape Fold Belt reveal that it comprises two main

structural domains:

1. A northern domain dominated by the low-relief Karoo

foreland basin displaying northward verging and

asymmetric folds

2. A southern domain that comprises of Cape

Supergroup rocks that displays a series of

approximately 8 km wavelength box folds and is

responsible for the high topography of the southern

Cape with elevations of up to 1500 m.

Not the

geophysic

al

informatio

n, only

some

geological

data.

The paper states that the southern Cape region of

South Africa has undergone at least two episodes of

structural inversion: first, compression forming the

Cape Fold Belt; subsequently, extension in the

Mesozoic. Fault geometry has remained constant in

both episodes.

Structures dip between 24° and 60°. The south is

composed of higher-angle faults, whereas the north

is composed of shallower-dipping faults.

Broadly, the model classifies the crust north of the

Swartberg Mountains, in the great Karoo, as “thin

skinned” and south as “thick skinned.” However, the

paper also states that the Cape Fold Belt cannot be

classified as thick- or thin-skinned; rather, it is more

useful to describe the deformation as being

controlled by a south-dipping mega-decollement that

exhibits aspects of both end members.

Considers the Plettenberg Fault to be imaged to at

least 12 km.

JN

Paton & Underhill Role of crustal anisotropy in

modifying the structural and

sedimentological evolution of

extensional basins: the Gamtoos

Basin, South Africa.

2004 The authors investigate the structural and sedimentological

evolution of the Mesozoic Gamtoos Basin, using 4700 km of

sub-surface data (2D seismic and boreholes) from the offshore

portion of the Gamtoos Basin.

The Gamtoos Fault has A 90° bend in the Gamtoos Fault trace

that we propose is caused by underlying structure.

In contrast, the rapid establishment of length in the Gamtoos

Fault and the localisation of displacement onto the basin-

Yes Data may be used in characterizing source zone(s)

and the Gamtoos fault.

Data provide no evidence for segmentation of the

Gamtoos fault, isolated depocentres, or intrabasin

faults, progressively coalescing during the syn-rift

interval.

The fold along the southern part of the fault is a

consequence of the accommodation of extension by

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bounding fault resulted in the rapid transition from a terrestrial

environment in the very earliest syn-rift episode (below seismic

resolution) to a deep water, anoxic setting within ~5 My of rift

initiation.

The Gamtoos basin is inferred to have been undergoing a

dominantly WSW-ENE extension orientation. There is no

evidence of deformation (oblique folding or faulting) associated

with strike-slip motion along either portion of the fault.

the unusual plan-view geometry of the fault (not due

to the complex interplay of compression and

extension, as suggested by previous workers).

Reznikov et al.

Structure of the Transkei Basin and

Natal Valley, Southwest Indian

Ocean, from Seismic Reflection

and Potential Field Data

Tectonophysics 397, 127-141.

2005 Marine geophysical data from the southern Natal Valley and

northern Transkei Basin, offshore southeast Africa, were used

to study the structure of the crust and sedimentary cover in the

area. The data includes seismic reflection, gravity and

magnetics and provides information on the acoustic basement

geometry (where available), features of the sedimentary cover

and the basin’s development.

2.5-D crustal models show that a 1.7–3.2-km-thick sediment

sequence overlies a 6.3F1.2-km-thick normal oceanic crust in

the deep southern Natal Valley and Transkei Basin. The

oceanic crust in the study area is heterogeneous, made up of

blocks of laterally varying remanent magnetization (0.5–3.5

A/m) and density (2850–2900 kg/m3).

Yes Evidence for seismicity and neotectonic activity in the

southern Natal Valley and northern Transkei Basin

that may be related to the diffuse boundary between

the Nubia and Somalia Plates.

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Roux Offshore Geophysical Data 2011 Presentation on the available 2D and 3D data at Petroleum

Agency of South Africa, on the offshore Mesozoic basins.

yes Considered in characterization of Gamtoos,

Plettenberg, and Cape St. Francis faults.

JN

Stamps et al. Lithospheric Buoyancy Forces in

Africa from a Thin Sheet Approach

2010 The authors use a thin sheet approach and the CRUST 2.0

model to compute vertically averaged deviatoric stresses

arising from horizontal gradients of gravitational potential

energy.

The analysis of geodetic data and earthquake slip vectors in

East Africa shows that:

Present-day Nubia-Somalia motion is consistent with the ~3

Myr average.

The kinematics of the plate boundary zone is best described

with a model that includes three minor sub-plates defined using

the distribution of seismicity (Victoria, Rovuma, and Lwandle).

Extension is directed ~E-W along the rift, with rates decreasing

from 6–7 mm/yr in the Main Ethiopian Rift and 3-4 mm/yr in the

central EAR, to <1 mm/yr south of Mozambique.

The Nubian Plate behaves rigidly at the current precision

level of the GPS measurements.

No JN

Stankiewicz et al.

(Stankiewicz, Ryberg,

Schulze, Lindeque,

Weber & De Wit)

Initial Results from Wide-Angle

Seismic Refraction Lines in the

Southern Cape.

2007 The paper reports the results from two wide-angle on-shore

seismic lines roughly parallel to each other. The lines are

spaced 200 km apart and extend from Fraserburg – Mossel

Bay and Graaff Reinet - St. Francis, respectively. Both profiles

start in the Beaufort Group intruded by Karoo dolerites about

30 km north of the Great Escarpment. The lines cross the

Cape Supergroup, the Cape Fold Belt, and the Uitenhage

group. The western profile also crosses the Kango and

Kaaimans Late Neoproterozoic-Cambiran inliers and the Cape

Granite Suite near George.

The focus of investigation is to resolve individual structures

within the crust

The resulting velocity model obtained from this study can

resolve structures 10 km across near the surfaces and

structures 40 km across anywhere at depth. The vertical

resolution varies with depth such that a body of a few km thick

can be resolved near the surface but not at greater depth.

SCCB (zone of electrically conductive material) placed

beneath southern Karoo basin & frontal CFB [408R]

N-most dipping to overturned Witteberg Group (Cape

Yes A line approximately 40 km north of the first

Witteberg outcrop is interpreted to mark the

northernmost deformation of the Cape Supergroup.

Images the listric nature of the Gamtoos and Kango

faults to a depth of 15 km.

Show dip on Kango Fault to increase to the east and

shallower and flatter to the west.

In the west, the Kango Fault is traced to ~12 km with

seismic refraction. In the east, the Kango Fault is

traced to ~14 km with seismic refraction.

Georeference

Figure 2 for

locations of

seismic lines.

Figures 4 and 6

present

observations

and

interpretations

as cross

sections.

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Supergroup) important marker. There is an asymmetric

synform immediately north of this line (i.e. ~140 km in the W

profile & ~100 km in E profile) [414]

• Karoo Group becomes very thin (< 2km) around 40 km

north of this point [414R]

• South of this point Karoo show thickening towards the

tectonic front of the CFB

• Marks approximate location of the most northerly exposed

thrusts of the Cape Fold Belt

• 40 km N of this point Karoo become very thin. Interpreted

as possible blind Paleozoic Thrust Fault (PTF in Figure 6)

(uncertain) [414R]. This could mark most N influence of

shortening [415L] deformation in the upper crust related to

the Cape Orogeny.

The higher seismic velocities of 5.4 to 5.8 km/s observed south

of the Karoo Supergroup mark the location of the Cape

Supergroup rocks within the Cape Fold Belt.

The Kango and Gamtoos fault are observed in the eastern

profile by two clear velocity anomalies. They separate the

Mesoproterozoic Namaqua-Natal Metamorphic complex from

more recent sediment trocks down to a depth of 15 km in

asymmetric listric basins. The western profile only crosses the

Kango fault where it is not imaged as clearly as in the eastern

profile. The hanging wall of the faults have slower seismic

velocities of ~4.5 km/s of the Jurassic Uitenhage Basin.

In both profiles, a high velocity region at depths of 10-15 km

correspond to the highest intensities of the Beattie Magnetic

Anomaly. In the eastern profile, this anomaly is 20 km wide

(between the 50 and 70 km marks), while the velocity anomaly

in the western profile reaches 70 km in width (between 40 and

110 km marks).

Beattie Magnetic Anomaly (BMA) is as much as 100 km wide,

(wider than stated elsewhere [415R]

The Cape Granite Suite and the Late Neoproterozoic Kango

and Kaaimans inliers are not obviously visible in the seismic

section and may therefore represent thin sheets or sills. The

high velocity zone up to 6.2 km/s beneath the Cape Granite is

indicative of the highly metatmorphized rocks of the Namaqua-

Natal Metamorphic Complex. These observations are

consistent with previous interpretations that the Neoproterozoic

inliers are basal sedimentary rocks of the Cape Supergroup

transported by south-dipping thrust faults with northward


36

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Is the data



transport directions.

The N- dipping tectonic fabric of NNMC is most likely related to

earlier Mesoproterozoic subduction / accretion of exotic and

suspect terranes [416L].

Stankiewicz et al.

(Stankiewicz,

Parsiegla, Ryberg,

Gohl, Weckman,

Trumbull & Weber

Crustal structure of the southern

margin of the African continent:

Results from geophysical

experiments.

2008 This paper combines and jointly interprets the different onshore

and offshore data sets (including wide angle refraction

[Stankiewicz et al., 2007], near-vertical reflection [Lindeque et

al., 2007], magnetotelluric profiles [Branch et al., 2007;

Weckmann et al., 2007a, 2007b], offshore refraction and

reflection seismics [Parsiegla et al., 2007, 2008],) along the

Western Karoo-Agulhas Profile. The model is consistent with

the model computed using only onshore shots [Stankiewicz et

al., 2007]. The improved ray coverage increased the maximum

depth of the model from less than 30 km to almost 40 km, and

many of the upper crustal features are better resolved.

The AFFZ marks the southern boundary of the African

continent [Talwani & Eldholm, 1973] & developed as a

consequence of dextral strike-slip motion between African and

South American continents during the Cretaceous break-up of

Gondwana [e.g., Barker, 1979; Rabinowitz & LaBrecque,

1979].

Research Model (Fig. 5) consistent with model computed using

only onshore shots [Stankiewicz et al., 2007], but increase

depth coverage (from less than 30 km to almost 40 km)

[p6,16]. It also confirms that thinning of the basin at profile

length of 100 km is a real feature (consistent with Stankiewicz

et al., 2007), and agree with proposed blind Paleozoic Thrust

Fault, which could mark the northernmost deformation of the

Cape Supergroup km [p6,16]

Moho depth reduce stepwise [p10, 24]. Moho discontinuity,

clearly visible as a high-velocity contrast.

• The Moho depth beneath the Karoo Basin is 40 km, and

slightly deeper (_42 km) beneath the CFB. The crustal

thickening beneath the CFB is consistent with Harvey et al.,

2001 & Nguuri et al., 2001, BUT Nguuri et al. consistently

locates the Moho ~5 km deeper. [7,20]

• South of the CFB Moho shallow to ~30 km at the present

coast. (Depth consistent with eastwest reflection profile of

Durrheim [1987],

• Farther south the crust continues to thin, albeit much more

gradually, for another 250 km, underneath the Agulhas

Bank, Outeniqua Basin and the Diaz Marginal Ridge,

Yes The improved ray coverage increased the maximum

depth of the model from less than 30 km to almost 40

km, and many of the upper crustal features are better

resolved. Provide important information on crustal

thickness and how it thins south to the AFZ, allowing

4 different segments to be identified. This is

important in characterization of three source zones.

The depth of 11–12 km the crust in the Agulhas

Passage, as well as the velocity structure that is also

typical of oceanic crust worldwide.

The Kango Fault has a low dip, is listric down to 10–

12 km.

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• Thins until it reached the Agulhas-Falkland Fracture Zone

(AFFZ). This fracture zone marks the continent-ocean

transition (COT). [p7, 21]

On the basis of Moho geometry, four segments of the crust can

be distinguished in both profiles:

• thick continental,

• stretched gradually thinning,

• steeply thinning, and

• thin oceanic crust [p12, Fig 11]

In the region of the abruptly decreasing Moho depth, in the

vicinity of the boundary between the Namaqua-Natal Mobile

Belt and the Cape Fold

Belt, [abstract – distinguish between NNMB & CFB?]. But in

sentence before this they say that it starts 40km inland

The oceanic crust (segment D) on both sections has the global

average thickness of about 7 km and a velocity structure that is

also typical of oceanic crust worldwide [p11, 29]

BMA

There is some correlation between the velocity model and

electrical conductivity image of Weckmann et al. [2007a] for

deeper features (Figure 10). Their model shows a zone of high

velocity at a depth of 15 km between profile km 60 and 90.

[p9, 23]

S edge of this anomaly is in the vicinity of the center of the

BMA [P9, 23], but a comparison shows that electrical

conductivity anomaly located beneath center of the BMA is too

narrow to be a possible source of the BMA [Weckmann et al.,

2007b]. [p10, 23]

Weckmann et al. show that these simple magnetic bodies

would produce response similar to BMA signature. The bodies

are separated by a fault, which cuts through at the same

inclination as the conductivity anomaly [p10, 23]

Lower crust anomaly

Zone of high seismic velocity (Vp > 7.0 km/s) in the lower crust

(from profile km 150 to the coast). [p12, p13] have 2

explanations

• Represents metabasic lithologies of Precambrian age in

the NNMB (see Dewey et al 1990), or

• Mafic intrusions added to the base of the crust by younger


38

Author Titlei Year


Is the data



magmatism.

Dewey et al (1990) suggested that ‘‘massive underplating’’ of

mafic magmas (~1050 Ma) was heat source for granulite-grade

metamorphism & crustal melting [p13, 32]

De Wit [2007] noted the surprising lack of seismic evidence for

mafic underplating of the Karoo magmas, whereas such

evidence is clear and abundant for the Parana´-Etendeka LIP

on the western margin. Authors argue that it did occur[p13, 34].

Authors favour model for magmatism adding thick intrusions of

gabbroic material to the lower crust, with mid-Jurassic Karoo-

Ferrar-Chon Aike Large Igneous Province the most likely

candidate

Stankiewicz et al.

(Stankiewicz, Parsiegla, &

De Wit)

An overview of geophysical

experiments across the continental

margins of Southern Africa.

11th SAGA Biennial Technical Meting &

Exhibition, Swaziland, 16-18 Sept 2009,

529-530.

2009 General report on 4 seismic reflection and refraction lines

along the western and southern continental margins. Nothing

new is added, but reference is made to preceding reports from

this programme including:

• Parsiegla et al., 2007, 2008

• Stankiewicz et al., 2007, 2008

• Bräuer et al., 2007

No JN

Stankiewicz Shallow structure in the Karoo

basin, South Africa, inferred from a

near-vertical reflection seismic

profile.

2011 A Near Vertical Reflection seismic profile from the Karoo Basin

between Beaufort West and Klaarstroom, was carried out

using controlled source vibroseis sweeps and a rolling spread

of recording geophones. 2-D travel time tomography was used

to compute P-wave and S-wave velocity variations for depths

down to ~300 m beneath the profile.

No JN


39

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Thomson Role of continental breakup, mantle

plume development and fault

reactivation in the evolution of the

Gamtoo Basin, South Africa

1999 Refers to seismic data in this study on the Mesozoic

extensional basin system along the southern margin of the

continent.

Extensional fault system that represent reactivation of Cape

Fold Belt thrusts

Envisage Cape Fold Belt structural control on structure of

Gamtoos Basin and larger Outeniqua Basin, but envisage only

minor role for the Agulhas-Falkland Fracture Zone on the

rotation of the Gamtoos Fault. Latter statement is based on

fact that shortening of the southern Gamtoos Basin and

substantially more inversion (with possible thrusting of basin fill

over the Recife Arch) are not observed.

N-S trending Gamtoos Fault is suitably orientated to

experience sinistral strike-slip movement with the Gamtoos

Anticline forming at a restraining bend in the hanging-wall

(McMillan et al., 1997). The inversion and 'pop-up' documented

in the St Francis Arch can be accounted for by sinistral strike-

slip.

Yes Supports models that interprets Mesozoic

extensional basins onshore to have formed by

extensional fault system that represent reactivation of

Cape Fold Belt thrusts.

Envisage Cape Fold Belt structural control on

structure of Gamtoos Basin and larger Outeniqua

Basin, but envisage only minor role for the Agulhas-

Falkland Fracture Zone on the rotation of the

Gamtoos Fault. Latter statement is based on fact that

shortening of the southern Gamtoos Basin and

substantially more inversion (with possible thrusting

of basin fill over the Recife Arch) are not observed.

N-S trending Gamtoos Fault is suitably orientated to

experience sinistral strike-slip movement with the

Gamtoos Anticline forming at a restraining bend in

the hanging-wall (McMillan et al., 1997). The

inversion and 'pop-up' documented in the St Francis

Arch can be accounted for by sinistral strike-slip.

JN

Uenzelmann-Neben Seismic characteristics of

sedoiment drifts: An example from

the Agulhas Plateau, SW Indian

Ocean.

2001 The Agulhas Plateau sediment drifts have been analysed with

respect to their seismic characteristics.

No JN

Uenzelmann-Neben Southeastern Atlantic and

southwestern Indian Ocean:

reconstruction of the sedimentary

and tectonic development since the

Cretaceous AISTEK-1: Agulhas

Transect. Report of the RV

"SONNE" cruise SO-1 82, Project

AISTEK-I (4 April to 18 May 2005).

Ber. Polarforsch. Meeresforsch.

515.

2005 A discussion of the methodology for data collection and

presentation of raw data.

No. Used

data from

this work

reference

in

subseque

nt papers

JN

Uenzelmann-Neben.

& Gohl

The Agulhas Ridge, South Atlantic:

the peculiar structure of a fracture

zone.

Marine geophysical researches,

25:305-319.

2004 Seismic reflection and wide angle refraction of Agulhas Ridge

(associated with AFFZ between 41°–43°S and 16°–9°E.

The Agulhas Ridge is a prominent topographic feature that

parallels the Agulhas-Falkland Fracture Zone (AFFZ). Seismic

reflection and wide angle/refraction data have led to the

No JN


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Is the data



classification of this feature as a transverse ridge.

Within the Cape Basin, the basement and part of the

sedimentary layers in parts are strongly deformed.

Agulhas Ridge is a transverse ridge of AFFZ & has undergone

uplift. 3 hotspots passed below AR. [317R]

Proposed decelaration of African Plate motion from 30m

(earlier than O’Conner et al 1999) [316R]

Interpret the anomalous topography of the Agulhas Ridge with

a large plateau in the northwest and two parallel, up to 2.5 km

high segments in the southwest as the result of the influence of

three hotspots on the development of the ridge’s structure.

Uenzelmann-Neben &

Huhn

Sedimentary deposits on the

southern South African continental

margin: Slumping versus

nondeposition or erosion by

oceanic currents? Marine Geology,

266, 6–79.

2009 This paper report the results from 2 seismic reflection lines

from SA continental shelf to deep sea. The focus of the study

on the distribution of Neogene sedimentary rocks and

circulation patterns .

Primary Conclusions

• Thin Cenozoic sedimentary column

• Erosion observed at specific water. Evidence for mass

movements(i.e. slumps) rare and localised.

• Erosion on-going

• Erosional patches correlate well with the activity levels of

• water masses active at the southern South African

continental margin.

• Erosion means study the Neogene climate variations at

the South African continental margin has lots of pitfalls.

Also shows that faults offset Pliocene units (Fig. 7).

Evidence is presented to disprove the size and extent of the

Agulhas Slump as proposed by Dingle (1977): erosional

processes rather than mass movement have given rise to the

bathymetric features. The Agulhas slump was indirectly cited

by Ben-Avraham (1995) as possible evidence of strong ground

shaking (possibly associated with the AFZ).

Width of zone of faults; location of northwesternmost fault

trace; dip of mapped faults is vertical to steeply dipping (Figs. 2

and 7).

Minimum apparent vertical stratigraphic offset of inferred

Pliocene horizon is 600–1,800 m across zone of faults

(excepting possible fault at base of continental slope). It is not

Yes. There is evidence of significant erosion on the

seafloor by the Agulhas Current. Erosion along the

Gamtoos fault may have created the scarp observed

by Roux (2011).

Evidence that faults in the AFZ offset Pliocene units

(Fig. 7).

Evidence is presented to disprove the size and extent

of the Agulhas Slump as proposed by Dingle (1977):

erosional processes rather than mass movement

have given rise to the bathymetric features. The

Agulhas slump was indirectly cited by Ben-Avraham

(1995) as possible evidence of strong ground

shaking (possibly associated with the AFZ).

Data provided thathelps to determine the width of the

AFZ; location of northwesternmost fault trace; dip of

mapped faults is vertical to steeply dipping (Figs. 2

and 7).

IN the AFZ the minimum apparent vertical

stratigraphic offset of inferred Pliocene horizon is

600–1,800 m across zone of faults (excepting

possible fault at base of continental slope). It is not

clear from the published figures (due to extreme

vertical exaggeration) how much of the apparent

vertical offset is due to initial drape on a sloping sea

bottom.

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Is the data



clear from the published figures (due to extreme vertical

exaggeration) how much of the apparent vertical offset is due

to initial drape on a sloping sea bottom.

Uenzelmann-Neben et

al.

(Uenzelmann-Neben, Gohl

& Ehrhardt)

Agulhas plateau, SW Indian Ocean:

New evidence for excessive

volcanism.

Geophys Res Letters, 26(13), 1914

– 1944.

1999. Seismic reflection and refraction lines focused on the southern

Agulhas plateau (APlat). Main aim of research is provide

insight on origin (Cretaceous or not) of the APlat.

A large number of extrusion centres were identified. Since the

sedimentary layers appear to be little affected by the

volcanism, that episode obviously ceased before onset of

sedimentation in Late Cretaceous times. We have not found

evidence for continental fragments within over-thickened,

predominantly oceanic crust.

No. JN

Uenzelmann-Neben et

al.

Cenozoic oceanic circulation within

the South African gateway:

indications from seismic

stratigraphy

2007 A compilation of the evolution of the oceanic circulation within

the South African gateway since the Early Eocene on the basis

of seismic reflection data is put forward and discussed.

A prominent feature in the sedimentary sequences of the

Northern and Middle Cape Basin is a marked increase in

seismic reflection amplitudes since the Early Pliocene (~4.4

Ma) in correspondence to a rise of cyclicity in reflector strength

(Figure 11). Since the strength of reflection amplitudes is a

measure for the impedance contrast, i.e., variations in P-wave

velocity and density, we have evidence for strong variations in

the composition of the deposited matter.

The investigation of sedimentary structures as imaged by

seismic reflection methods provides information on the current

systems responsible for the generation of those structures. We

are thus able to construct a model for the chronological

evolution of the currents in the gateway of South Africa. This

model contains important information on the climatic evolution

of southern Africa.

No JN

Uenzelmann-Neben et

al.

Palaeoceanographic interpretation

of a seismic profile from the

southern Mozambique Ridge, SW

Indean Ocean.

2011 Seismic reflection data from the southern Mozambique Ridge,

Southwestern Indian Ocean, show indications for a

modification in the oceanic circulation system during the

Neogene.

No JN

General geophysics

Davidson & Smith Geophysical survey report for

Thyspunt Eskom site surveys South

Africa.

2007 Report summarises the results of a marine geophysical survey

within a semi-circle of 8 km radius with its origin at the

proposed Thyspunt site and used the following techniques:

No JN


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Author Titlei Year


Is the data



(Fugro report) • Multibeam echo sounder (MBES)

• A single beam echo sounder (SBES)

• Sub-bottom profiling survey using a high resolution

seismic profiling system

• Side scan sonar survey

• Magnetometer survey

The fine sediment in the central portion of the central basin

appears to be lithified to some extent and has some unusual

features including wide scale fracturing, slumping and the

development of knolls and step structures. Asymmetrical

furrows are the surface expression of the planes along which

slumping occurred. Erosive processes have then deepened the

furrows.

Faults and slump features do exist in the survey area but no

information as to when they were last active was obtained.

Horwood Thyspunt 8km Radius Marine

Survey: Structural Geology Report

2009 Report includes an assessment of offshore data collected

during an offshore survey undertaken by Fugro SA for Eskom

from 8th to 18th November 2006 and a follow up survey

undertaken between the 28th May and the 25th June 2007,

using sidescan sonar and multibeam bathymetry.

A number of NW/WNW fractures were identified, subparallel to

the bedding trend. At least one of these fractures is postulated

to be a fault, which may intersect the shoreline outside of the

area of exposed outcrop at Klippepunt.

A series of pervasive, small NE trending faults displace the

WNW trending faults and are therefore interpreted as younger

It is postulated that the sedimentary features which have been

previously referred to as slumps, are most likely erosion

channels, however scrutiny of the existing data is necessary to

test this hypothesis.

No evidence of recent faulting has been observed in the 4

charts covered by this report.

No JN

Steward & Smith Geophysical survey report for

Thyspunt inshore site survey for

Eskom, South Africa.

(Fugro report)

2007 An inshore marine geophysical survey was conducted by

Fugro off the Thyspunt site.

The inshore survey covered two separate blocks, identified as

the West block and East block respectively.

The following techniques were used:

• Multibeam echo sounder (MBES)

No JN


43

Author Titlei Year


Is the data



• Sub-bottom profiling survey using a high resolution seismic

profiling system

• Side scan sonar survey

• Magnetometer survey

The rocky portions of the shoreline and inland of Thyspunt

consist of sandstone belonging to the Table Mountain Group

and it is probable that the sandstone identified in the marine

survey is the same rock type. The sandstone has marked

jointing patterns and possible faults.



44

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General

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Report No. 2009-0027, 11pp.



53

Steward & Smith. (2007). Geophysical survey report for Thyspunt inshore site survey for Eskom,

South Africa. Fugro Report Number MZ581za-01-RPT-03-01, NSIP-NSI-019130#P1-215.


54

Table 3.2. Data Summary Table – Regional Tectonic Setting Thyspunt PSHA

Author1 Title

Year

Description and Relevance to SSC

Is the data used in the

SSC model?

(yes, no)

Discussion of Data Use GIS Code Originator

Tectonic Models and Features

Booth, PWK

Conference

abstract

11th SAGA

Biennial Technical

Meeting and

Exhibition,

Swaziland, 16-18

September 2009,

481-485

A review of the structural

geology of the Cape Fold Belt

and challenges towards future

research.

Keywords: Thrust faults, trust

stacking, transpressional

tectonic model

2009 Both the Andean (subduction of oceanic lithosphere because of

seafloor spreading) and strike-slip (transpressional) tectonic

models can be used to explain the structural evolution of the

Cape Fold Belt [pg481]. The transpressional model explains the

en echelon (fold) and fault structures in the Cape Fold Belt

(CFB).

Faults and folds patterns indicate major thrust stacking

especially in the Witteberg and Table Mountain Groups [pg482].

Decoupling along major faults in the major part of the CFB may

be largely in the upper crust therefore supporting the thin-

skinned tectonic models [pg482].

No

Here two models are

considered to explain the

tectonics in the CFB; the

Andean and the

transpressional. These two

models justify the folding and

the faulting. The thin-skinned

tectonic model (indicating

that fault do not run beyond

the upper crust) is also used

for the CFB.

RS

Johnson MR, Van

Vuuren CJ, Visser

JNJ, Cole DI, de V

Wickens H,

Christie AMD and

Roberts DL

Chapter 12

269-317

Sedimentary

Basins of the

world, 3: African

Basins( RC Selley,

ed)

The foreland Karoo Basin, South

Africa

Keywords: passive margin,

clastic wedge, Karoo Trough,

axis of deposition

1997 The Karoo basin is largely underlain by the stable Kaapvaal Craton

and the Namaqua-Natal belt and is bounded to the south by the Cape

Fold Belt. The Cape Supergroup contains a passive margin clastic

wedge of up to 8 km in thickness. The wedge was from the northern

cratonic provenance [pg269]. The Karoo basin consists of a retro-arc

foreland basin placed behind an island arc. The magmatic arc

associated with the subduction zone may have been located in

southern South America and the Atlantic Peninsula. This subsidence

occurred in the Karoo Trough (linear belt) along the southern boundary

of the Karoo basin. This basin reflects maximum subsidence (shown by

the thickness) which took place in a linear belt (Karoo trough) along the

southern edge of the basin.

A northward shift of the Karoo trough axis and a westward migration of

the Natal trough axis happened between early Palaeozoic and Permian

periods. The Karoo basin was constructed from the late Carboniferous

to recent by gradual subsidence of the cratonic crust. The basin might

have subsided due to ice loading. Loading through folding and

thrusting in the Cape Fold Belt and the sedimentary loading may have

No RS


55

Author1 Title

Year



SSC model?

(yes, no)


been responsible for basin subsidence, especially in the Karoo trough

where the sediments were up to 10km thick. The Cape Fold Belt

formed a segment of the Gondwanide Orogen (e.g. Du Toit, 1937). The

Cape-Karoo sequence fits a classic geosynclinal cycle. However a

major glacial episode may have interposed between the pre-orogenic

stage (Cape Supergroup) and the pre-flynch stage (Prince Albert-

Collingham formations). The Cape Fold Belt is thought to have been a

zone of weak crust that was compressed by the northern rigid

Namaqua-Natal belt and the Saldania granite. Some of the lower units

of the Karoo basin have also been folded [pg305].

The Southern Cape Conductive Belt is observed south of the Karoo

basin. From what de Beer et al. (1982) suggest, this conductive belt

may indicate denser oceanic crust that was obducted against the

continental margin during the Late Proterozoic Pan-African Orogeny. A

less prominent trough is situated to the east of the basin. This may

have been an indication of the reactivated of the Early Palaeozoic zone

of rifting.

Curtis ML and

Hyam DM

Journal of the

Geological

Society, London

Vol 155, 115-129

Late Palaeozoic to Mesozoic

structural evolution of the

Falkland Islands: a displaced

segment of the Cape fold Belt

1998 At present, the Falkland Island is situated on the South American

Plate. This geological entity is believed to be a displaced Gondwana

Orogenic belt segment. Data is this paper makes it possible to

correlate the geology, timing of deformation and structure of the

Falkland Island and Cape Fold Belt. Based on this, a conclusion is

made that the Falkland Islands have been tectonically rotated 180°.

The original position of the island was south-east off the south coast of

South Africa and this position could be evidence of the extent of the

Cape Fold Belt.

Yes The Agulhas Falkland

Fracture Zone lies parallel to

the South African continental

shield and is a transform fault

along which the Falkland

Islands were displaced and

tectonically rotated towards

the South American plate

RS

De Beer CH

Internal Report

written for the

Seismology Unit

(no report number)

Geology and tectonics of the

Thyspunt site, Humansdorp.

Keywords: Thyspunt, Cape

Orogeny, extensional tectonics

2000 Although the area around Thyspunt (underlain by the Nardouw

Subgroup) is relatively devoid of well-developed faults and

suggests a reduced seismic risk, it is bound by regionally large

fault zones (Ceres-Cango (Kango)-Baviaanskloof and

Worcester-Mossel Bay) [pg i].

Two Permo–Triassic major tectonic events affected the Karoo

and Cape Supergroups; the compressive Cape Orogeny and the

extensional Mesozoic tectonics [pg4]. CCBFZ and WMFZ

No Structures that were caused

during the break-up of

Gondwana may be

reactivated by subsequent

tectonic events.

RS


56

Author1 Title

Year



SSC model?

(yes, no)


present the most important zones of weakness that reflect deep

crustal inconsistencies and fragility [pg5]. Some of the faults in

between these fault zones extend offshore into the Pletmos,

Algoa and Outeniqua Basins.

Structures produces during the break-up of Gondwana created

imbalances and anisotropies which may be reactivated by later

tectonism [pg5]. The Gamtoos and Kouga Faults are the east- to

southeastern trending structures most proximal to the Thyspunt

Site.

Booth PWK and

Shone RW

Full paper

Journal of African

Earth Sciences,

34, 179-190

A review of thrust faulting in the

Eastern Cape Fold Belt, South

Africa, and the implication for

current lithostratigraphic

interpretation of the Cape

Supergroup.

Keywords: thrust faulting, thrust

sheets, strike-parallel belts.

2002 Closely-spaced thrusting is present in all units of the CFB in the

Eastern Cape. This is seen in thrust sheets. Slicken-sides and

S-C cleavages show a sense of direction that indicate a

northward movement of the thrusts. In Port Elizabeth, the

movement is northeast-ward [pg187]. It looks like this movement

is away from the Thyspunt site.

In Port Elizabeth, thrust faults generally dip at shallow to

moderate angles on an azimuth of 200°. Imbricate faults that are

associated with thrust planes have southwesterly dip angles. In

Kareedouw (150 km northeast of PE), there are at least 3 fore-

and back-thrusts sheet. The width of the thrust sheets ranges

between 2 km (Riverside nearby Kareedouw) and 4 km

(Uniondale) and 5km (Kareedouw).

[pg183]

One should be careful when interpreting thrust sheets (of up to 5

km wide). Most should be regarded as tectonostratigraphic as

opposed to lithostratigraphic [pg188].

The thrust sheets may extend from Uniondale to Port Elizabeth,

distance of some 300km [pg189].

No Fault dip and style of faulting

In Port Elizabeth, thrust faults

generally dip at shallow to

moderate angles on an

azimuth of 200°.

In Uniondale, thrust sheets

have an orientation of

Azimuth: 180° and dip:

variable angles.

In Steytlerville (~150 km NW

of PE), thrust faults an

orientation of

Azimuth: 193° and dip: not

shown.

In Port Alfred, thrust faults

have an orientation of

Azimuth: 218° and dip:

average 31°.

RS

Johnston ST The Cape Fold Belt and 2000 A late tectonic event of dextral transpression across the Cape Yes Although the events talked RS


57

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Full Paper

J. of African Earth

Science, 31 (1), 1-

13

Syntaxis and the rotated

Falkland Islands: dextral

transpressional tectonics along

the southwest margin of

Gondwana.

Keywords: CFB syntaxis, dextral

transpressional tectonics

Fold Belt (CFB) resulted in the Cape Syntaxis and the Port

Elizabeth Antitaxis. At the time of separation of South America

from Africa, the Port Elizabeth hinge regions formed a zone of

weakness (fracture) along which the Falkland-Agulhas Fracture

Zone propagated [pg11].

The pattern of faults (and folds) is consistent with an overall

dextral strike-slip deformation. See also Cobbold et al., (1992).

The second bend of the Cape Fold Belt in Port Elizabeth shows

thrusts that have been rotated by more than 20º clockwise. A

second major curve in the CFB comparable in scale and attitude

to the Cape Syntaxis in the Port Elizabeth area (the Port

Elizabeth Antitaxis). This bend is now obscured by younger

sediment [pg4].

The bend is also host to curved faults which may have resulted

from the drag along the dextral Agulhas-Falkland Fracture Zone

[pg5].

The Cape Syntaxis, Port Elizabeth Antitaxis and the rotation

(~180º) of the Falkland Islands (a result of orocline formation)

may be proof of dextral transpression (transcurrent strike-slip

motion and oblique compression) [pg9].

about here are not dated

here, the author mentions a

late event of left-lateral strike-

slip deformation. The two

bends (indicating rotation) of

the CFB Syntaxis and the PE

Antitaxis are host to curved

faults.

The position of the Falk

Islands is evidence of this

rotation (180°).

De Beer CH

Full paper

J. of African Earth

science, 21 (1),

157-169

Fold Interference from

simultaneous shortening in

different directions: the Cape

Fold Belt syntaxis

Keywords: oroclinal orogeny,

antitaxis, thin-skinned

deformation

1995 The structure of the Cape Fold Belt syntaxis (sign of oroclinal

orogeny) is due to the fold interference (indicated a

constructional deformation – constructional strain is recorded in

the Witteberg Group) from non-coaxial fold belts of roughly the

same age on a larger non rotational arc formed by moulding of

the orogen around the Kaapvaal craton.

The Cape Fold Belt is divided into 3 sections:

Northern branch which trends NW and has upright 1st order folds

and monoclines.

Southern branch which trends east. Intense deformation is

No The two branches of the CFB

have the same age.

The Cape Fold Belt syntaxis

was formed buy compression

(shortening) which also

resulted in fold interference.

RS


58

Author1 Title

Year



SSC model?

(yes, no)


observed here and this is indicated by recumbent plus second

order folds.

Curved intersection between the two branches. This is the

syntaxis.

Based on the work done by Halbich et al. (1983), this paper

supports that the Ceres Arc (at the syntaxis) registers 278 Ma.

The post-tectonic faults have complicated the fold pattern.

Both the syntaxis and the antitaxis could have been formed by

concurrent shortening (although the percentage is low) in the

north and east direction. This is in addition to thin-skinned

deformation. The syntaxis structure was also probably formed by

thin-skinned processes. The syntaxis should therefore be

regarded as a result of both large non-rotational arc and 2

smaller antitaxial arcs developed during the time of the Cape

Orogeny [pg168].

Booth PWK,

Brunsdon G,

Shone RW

Full paper

Gondwana

Research,

7(1), 211-222

A duplex model for the eastern

Cape Fold Belt: evidence from

the Palaeozoic Witteberg and

Bokkeveld Groups (Cape

Supergroup), near Steytlerville,

South Africa

Keywords: duplex, imbricates,

tectonic events

2004 A large duplex structure has formed in the southern part of

Gondwana in the late Palaeozoic. This structure includes north

verging thrust faults associated with folds.

A 500 m displacement is observed in the Jackalsbos thrust. This

thrust is the only one in the duplex that is linked through dipping

imbricates to the Baviaanskloof thrust (south of this area).

During the break-up of Gondwana, normal faults and more

commonly, thrust faults, were formed (during the Mesozoic). The

Cape and Karoo Supergroups including the pre-Cape basement

were deformed in the by a regional compressive event during

the Carboniferous/Permian. The nest event was extensional

because of the break-up of Gondwana. As a result half grabens

were formed [pg211].

Deformation in the rocks of the Karoo and Cape super group

extend 250 km from the coast. The intensity of deformation

decreases with northward direction. This paper suggests 4

paroxysms (dated by Ar-Ar step heating from the south

No Four tectonic events are

suggested here. These

occurred between 278 and

210 Ma.

RS


59

Author1 Title

Year



SSC model?

(yes, no)


direction) which occurred between 278 and 210 Ma. This is less

than the 5 tectonic events that are usually mentioned (e.g.

Halbich et al. 1983).

The eastern Cape Fold Belt is dominated by thrust (can be

closely spaced) and fold (with rotated fold axes during thrusting)

structures [pg216, 217].

These authors proposed a hinterland-dipping duplex model

(represented by the Jackalsbos Thrust and steeply dipping

imbricates connecting with the roof thrust). Small scale duplexes

have been reported in the eastern Cape and this can account for

deformation of the lower Wittenberg group [pg219].

Normal faulting characterise the extensional tectonism in the

Cape Fold Belt during the Mesozoic (break-up of Gondwana)

[pg219] whereas strike-slip faulting is evidently associated with

the Agulhas Fracture Zone and these show the late part of the

deformation [pg220].

Hempel, C., Booth,

PWK, Shone RW

and Anderson CR.

Conference

Abstract

Geoscience Africa

Abstract Volume 1

266- 267

Microstructures in thrust zones

of the Table Mountain Group

(Cape Supergroup) near

Laurie’s Bay, Port Elizabeth,

South Africa: their use as

kinematic indicators.

Keywords: microstructures,

tectonic transport,

2004 Sense of movements on thrust faulted regions can be resolved

determined by microstructures (S-C cleavages, rotated

porphyroblasts and mica fish). The microstructures in the Table

Mountain thrust zones near Laurie’s Bay (Port Elizabeth) show

that tectonic transport was from southwest to northeast during

the compressional phase of the Cape Orogeny.

Dextral movement is recorded along the Laurie’s Bay Fault (700

m west of the bay). This fault forms the contact between the

Table Mountain Group and the Pre-Cape rocks.

No Left lateral movement along

the Laurie Fault is associated

with transport tectonic load

from the SW to NE direction.

RS

Brunsdon G and Faulting of the Wittenberg Group 2009 Different characters of thrust faults (older) in the study area (14 No There are no dates of RS


60

Author1 Title

Year



SSC model?

(yes, no)


Booth PWK

Conference

abstract

11th SAGA

Biennial Technical

Meeting and

Exhibition,

Swaziland, 16-18

September 2009,

500-505

Rocks, Steytlerville, Eastern

Cape

Keywords: shallow low-angle

thrust faults, normal and strike-

slip faults,

km of Steytlerville):

shallow south dipping low-angle

steep south dipping fore-thrusts planes

rarely north dipping back thrusts

These thrusts faults are primarily reactivated by later steep

dipping normal faults. The youngest common (present

throughout the study area) type of faulting is strike-slip [pg500].

Because of faulting and thrust stacking in the Witteberg Group,

some argillaceous units have been omitted and the more

resistant arenaceous rock units have been repeated. The

Witteberg Group has also been extensively folded and the

associated faults use the limbs of the faults are movement

planes [pg501].

The large Grootrevier East normal fault system and the

Jackalsbosch thrust were displaced by an en echelon strike-slip

fault in the study area.

activation or reactivation.

Although younger strike-slip

faults are common the area

but younger normal faults are

suggested to have

reactivated pre-existing thrust

faults.

Gresse PG,

Theron, JN, Fitch,

FJ and Miller, JA.

Special paper

In: Inversion

tectonics of the

Cape Fold Belt,

Karoo and

Cretaceous basins

of Southern Africa

Tectonic inversion and

radiometric resetting of the

basement in the Cape Fold Belt

Keywords: tectonic events,

stress direction, principle slip

direction

1992 Thin strips along faults that are between the Kango and

Kaaimans inliers represent remnants of the southern limbs to the

mega anticlinoria. These strips dip to the south. The Kango and

the Gamtoos faults may contain several thrusts of the Cape age.

These structures which are characterised by near-horizontal

thrusts and intense duplexes occurred before the normal faulting

[pg221].

Two 40Ar/39Ar ages are highlighted here; ± 258 and 278 Ma.

These ages also agree with Halbich et al. ages. These ages are

also thought to be individual tectonic deformation events that

shaped the Cape Fold Belt. Can these be the second and third

tectonic events in the Cape Orogeny?

Negative inversion structures include curving normal fault

segment that form rift features as long as 300 km. the segments

No Principle stress direction

during Cape folding: 184/00°

Principle slip direction during

thrusting is approximately

165/27°

From 40Ar/39Ar ages

Second event? ± 278 Ma

Third event? ± 258 Ma

RS


61

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SSC model?

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have a throw of 6 km toward the S. normal faults are thought to

have followed pre-existing thrust surface that were relate were

related to positive inversion. Although not in the Thyspunt

320km radius, an age of 177 Ma is proposed to have been a

reactivation of the basement and inversion along the Worcester

fault [pg226].

Halbich IW, Fitch,

FJ and Miller JA.

Full paper

In: Geodynamics

of the Cape Fold

Belt. Special

Publication of the

Geological Society

of South Africa,

Vol 12, 149-164

Dating the Cape Orogeny

Keyword: deformation phase,

cleavage, tectonic events

1983 From 40Ar/39Ar step heating ages, Halbich et al. interpreted 5

ages that are thought to indicate a multiple event deformation

phase of the Cape Fold Belt.

278 ± 2 Ma: S1 cleavage and the Swartberg folds formed.

Deformation even affected the youngest Dwyka glacial rocks. S1

may have been widespread but overprinted except at Swartberg

or only fully developed here.

258 ± 2 Ma: S2 cleavage and the Outeniqua folds are formed.

Small-scale Meirings Poort folding. S2 is the best and widely

developed associated with the highest metamorphic grade and

tectonism in the Cape Fold Belt.

247 ± 3 Ma: D2 on the Outeniqua folds (in George Anticlinorium)

and S3 forms. Shearing of the Groot Haelkraal granite and large

folds in the south part of the lower Beaufort and Ecca Groups.

230 ± 3 Ma: Final deformation phase of pre-Beaufort rocks.

Listric thrusts in the lower Beaufort and mild fold phase with

fanning of axial plane on S3.

215 ± 5 Ma: Uplift of the Cape Orogeny and extension? And

then kink phase. This time is also thought to be a time of mantle

doming (before the onset of Karoo magmatism).

Yes Five tectonic events in the

Cape Fold Belt; 278, 258,

247, 230 and 215 Ma.

All these with error margins

of ± 2 to 5 Ma.

RS

Halbich IW A tectogenesis of the Cape Fold 1983 Similar to Halbich et al. (1983), this paper also suggests 5 step- No A single deformation phase RS


62

Author1 Title

Year



SSC model?

(yes, no)


Full paper

In: Geodynamics

of the Cape Fold

Belt. Special

Publication of the

Geological Society

of South Africa,

Vol 12, 165-175

Belt

Keywords: paroxysm,

deformation, cleavage

paroxysms of the Cape Fold Belt deformation.

Early Permian; 278 ± 2Ma: Development of the Kango

Anticlinorium and the proto-Swartberg. 35% horizontal

shortening. Asymmetrical folds resulted from flexural slip and

decollement along contacts.

Early mid-Permian; 258 ± 2 Ma: Development of the George

Anticlinorium with 70% horizontal shortening (plus proto-

Outeniqua and Langeberg ranges). Overfolding caused

isoclinals to almost recumbent structures. From the S2 cleavage

date, large 20 km-thick pile of thrust and folded rocks.

Late to early Triassic. For some reason the S3 cleavage

development (247 ± 2 Ma) is discussed under the second

paroxysm in this paper. But according to Halbich et al. (1983)

this solution cleavage forms the third event. In this paper, the 3rd

paroxysm is marked by a steeply south-dipping S3 cleavage

(shear and solution). This is found in the Outeniqua and

Swartberg ranges.

Mid to late Triassic. Kink bands and minor shears that are

correlated with 230 ± 3 Ma. The lower Beaufort and older rocks

are deformed into upright folds with low amplitude. S4 (could this

be the fanning S3?)

Final paroxysm

of the CFB is composed of 5

paroxysms/ tectonic events.

These are mostly calculated

from crenulation cleavages.

278 ± 2Ma

258 ± 2 Ma

247 ± 2 Ma

230 ± 3 Ma

A final paroxysm is not given a

date here but could be 215 Ma

(see Halbich et al. 1983).

Tankard A.,

Welsink, H, Aukes,

P, Newton R and

Stettler E.

Full paper

Marine and

Petroleum

Geology, 26

Tectonic evolution of the Cape

and Karoo basins of South

Africa

Keywords: Cape Orogeny,

intraplate tectonics, mantle flow

2009 Subsidence (represented by the Karoo and Cape basins) is a

product of lithospheric deflection because of mantle flow plus

long distant subduction. The two basins have undergone crustal

uplift, lengthy regional subsidence and subsidence controlled by

first order basement faults [pg1380]. Two large-scale episodes

of intermittent subsidence are well represented by the Cape and

Karoo basins.

In contrast to Johnston (2000), suggesting that the Falklands

Plateau has not been rotated. Tankard et el. argue that there is

Yes Cape Orogeny is up to 250-

215 Ma.

The Karoo and Cape basins

have been crustally uplifted.

Basement faults controlled

the long periods of regional

and subsequent subsidence

in the two basins. These

authors also suggest that

GIS_X1000_F6_Ta

nkard_et_al_2009.t

if

GIS_S1017_F4b_T

ankard_et_al_2009

.tif

GIS_S1018_F3_Ta

nkard_et_al_2009.t

RS


63

Author1 Title

Year



SSC model?

(yes, no)


1379-1412 no seismic evidence of microplate boundaries and that the time

interval (from 40Ar/39Ar dating) for this is too short for this kind of

rotation [pg1381]. The southern edge of the Namaqua crustal

block is interpreted as a volcanic rift margin with a WNW

orientation and a thick crust. The Namaqua thrust front has a 9°

down-to-the-north dip and has vertically displaced the Moho by

14km [pg1385].

Deep burial studies by Rowsell and de Swardt, 1976) suggest

an 8 km of uplift and erosion. The southern margin of the

Namaqua plate (intraplate suture zone) is typical of N-dipping

shallow crustal fault displacing the Moho. Basin formation and

deformation is controlled by the reactivation of this suture zone

[pg1386].

Large-scale subsidence continued in the Devonian but not

accommodated by faulting. [pg1390]. The Cape Fold Belt is

mostly thick-skinned (strike-slip orogen) but the foreland edge is

thin-skinned. There are two main subsidence and deposition

events in the Karoo basin, separated by a hiatus of 10 Ma.

Burial studies show a 3 km uplift and erosion north of the CFB.

In the Permian times, before the Cape orogeny the early Karoo

basin was subjected to subsidence by vertical displacement of

rigid basement block decoupled along the crustal-scale

boundary faults [pg1397]. Although the individual blocks

responded in different ways, subsidence was primarily controlled

by mantle flow. Some strike-slip faults in the Karoo basin have

been activated by older displaced principal shear zones. This

subsidence was terminated by regional left-lateral strain

(including the CFB and Hartbees-Doringberg shear zones) [pg

1407].

Based on the en echelon faults, folds, flower structures and uplift

along the Worcester Fault, the Cape fold belt is a sinistral strike-

subsidence was controlled by

mantle flow.

Formation and deformation of

these basins are a result of

the reactivation of the

Namaqua suture zone

(Thrust in the Namaqualand

regions has displaced the

Moho by 14 km).

Both thick and thin-skinned

models are used for Cape

Orogeny. In contrast to

Johnston (2000), the CFB is

thought to be a right-lateral

belt.

if

GIS_S1019_F20_T

ankard_et_al_2009

.tif

GIS_S1020_F19_T

ankard_et_al_2009

.tif

GIS_S1021_F4a_T

ankard_et_al_2009

.tif

GIS_S1022_F13_T

ankard_et_al_2009

.tif


64

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Year



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(yes, no)


slip belt (of Worcester and Cango (Kango) shear zones) due to

the Saldanian orogenic event and is linked to the reactivation of

the Namaqua suture (which became a plane of detachment).

The Karoo is classified as a transtensional foreland basin that is

thought to be a result of the boundary forces associated with the

Cape Fold Belt and the en echelon fault zones [pg1408].

Lock, BE

Full paper

Geology, 8

15-39

Flat-plate subduction and the

Cape Fold Belt of South Africa

Keywords: subduction, margin,

tectonism, plate, convergence

1980 The Cape Fold Belt is located some 1000 km from the

continental margin. The oceanic lithosphere subducted along the

Andean margin of the continent was merged with part of the

overriding continental crust of Gondwana [pg35]. Some of the

convergence at the plate boundary may have been shortened

during deformation within the Gondwana plate as opposed to by

normal subduction. This deformation was also concentrated in

the intraplate Cape Fold Belt.

The Cape Fold Belt deformation includes south-dipping high-

angle thrust faults and flat-lying disharmonic folds. When the

South Atlantic was rifting (early Cretaceous), the faults we

reversed and became down-thrown to the south with a strong

right lateral direction. There are also macro-scale asymmetric

anti- and synclines which are overturned toward the south and

minor thrust nappes [pg36].

Opposing Gough (1973), the residue of mantle melting is of low

density due to the partitioning of the Fe into the melt.

The Cape Fold Belt formed some 2000km from the plate margin

of the Pacific (coastal region of Chile). Thus, the flat-plate

subduction (since model can explain belts of tectonism that are

far into the middle of the overriding plate) may have happened

under the southwestern Gondwana in the late Palaeozoic [pg37]

The region of the Cape Fold Belt is thought to be relatively

No Overthrusting of the oceanic

slab in the Andean margin

was in the late Palaeozoic.

Because of the distance of

the CFB from the continental

margin, a flat-plate

subduction model is

suggested. This model

explains why the CFB is

resistant to tectonism. In this

case, the oceanic plate was

not subducted but was

overthrusted together with

the continental plate (late

Palaeozoic).

RS


65

Author1 Title

Year



SSC model?

(yes, no)


resistant to tectonism because of the flat-slab subduction.

Instead of being subducted, the oceanic plate was overthrusted

with the continental crust in the late Palaeozoic. Plate

convergence, tectonic deformation and crustal shortening also

took place [pg38]

Gough DI

Full paper

Nature (Physical

Science), 245

93-94

Possible linear plume under

southernmost Africa

Keywords: conductivity,

anomaly, melt, mantle

1973 Large negative isostatic gravity anomaly with a minimum of -

80mgal exists in the eastern part of the Cape Fold Belt.

Along with the positive electromagnetic conductivity anomaly in

the western side of the Cape Fold Belt (suggested by Gough et

al, 1973), both these anomalies might indicate an east-trending

zone of high temperature in the upper mantle.

Assuming that both anomalies come from the same source, the

gravity data may indicate a mass deficiency at a depth of no

more than 50km which resulted from high temperatures.

According to Lock (1980), this would have resulted in a

temperature anomaly of 5000°C.

Because of this a component of composition had to be factored

in and it was deduced that there must have been preferential

melting of low density minerals in the source region of the

plume.

No RS

Goedhart ML and

Booth PWK

Conference paper

11th SAGA

Biennial Technical

Meeting and

Exhibition,

Swaziland, 16-18

September 2009,

510-513

Early Holocene extensional

tectonics in the South-Eastern

Cape Fold Belt, South Africa

Keywords: intraplate, slip rate,

recurrence rate,

palaeoseismicity

2009 Surface rupture occurred along the Kango Fault at the start of

the Holocene. This 84km long section was reactivated by the

palaeo-earthquake close to Oudtshoorn. The Kango Fault can

go to depths of over 10 km (see Lindeque et al., 2007).

These are the dates obtained from the trench investigation at

which the fault was active [pg510]

12. 206 ± 0.723 Ka

8. 878 ± 0.452 Ka and most probably

10. 620 ± 0.509 Ka

Samples obtained at the base of the trench are about 115 Ka

(Pleistocene). Other samples are early to late Holocene. The

No Surface rupture along the

Kango Fault is dated (OSL)

10 620 ± 509 years.

Kango Fault dips to the south

RS


66

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(yes, no)


age of the oldest exposed sample from the trench indicate

recurrence rates of 106.8 ± 5.5 Ka, characteristic of intraplate

settings. The fault has a vertical displacement of 2 m. The slip

rate on the Kango Fault is 0.0187 – 0.0208 mm/yr [pg511].

The Cape Isostatic Anomaly (E-W gravity anomaly trough from

PE to Willowmore) is a potential tectonic driver and may reflect

the roof of the former fold belt. New low-level seismicity data of

the Kouga and Baviaanskloof Faults show that they are under

strain and could be capable. The reactivated segment (Kango?)

east of Skilpaadbeen thrust near Willowmore may have had

more than one event of surface rupturing in the Quaternary.

Bate KJ and

Malan JA

Full paper

In Inversion

Tectonics of the

Cape Fold Belt,

Karoo and

Cretaceous Basins

of Southern Africa

61- 76

Tectonostratigraphic evolution of

the Algoa, Gamtoos and

Pletmos Basins offshore South

Africa.

Keywords: tectonostratigraphy,

negative inversion

1992 The break-up of Gondwana resulted in extensional stresses that

reactivated tectonic lineaments [pg65, 71]. Active rifting also

existed along these lineaments. The Cape Fold Belt offshore is

displayed as extensional basins that are thought to have been

formed by reactivation of thrusts faults in the Cape fold Belt.

The faults (Gamtoos, Port Elizabeth, St Croix, + Plettenberg)

bounding the extensional basins have pronounced curvature

and they have been rotated clockwise about a northeast

trending hinge to southerly trends. These faults extend offshore

South Africa and are cut by the Agulhas-Falkland Fracture Zone.

The faults have also been reactivated by extensional stresses

[pg65].

The sequences in the depocentres in the basins show evidence

of multi-phase movement history of the faults bounding the

extensional basins [pg65].

The break-up of Gondwana resulted in negative inversion of the

thrust faults of the Cape Fold Belt. This might have been the

time where the Mesozoic half grabens in the southern offshore

began [pg65] See also Dingle et al., 1983. The Gamtoos Faults

No Reactivation of tectonic

structures (lineaments, rifts)

was accompanied by the

break-up of Gondwana.

Style of faulting on Gamtoos:

Normal with a throw of 10km

[pg63]

Extensional basins in the

CFB were formed by the

reactivation of thrusts. A

multi-phase movement along

these faults is suggested.

Because of the break-up of

Gondwana, thrusts in the

CFB were negatively

inverted.

RS


67

Author1 Title

Year



SSC model?

(yes, no)


may be segmented including the Elandsberg and Gamtoos as

the segments [pg71]. Dip-slip and small angle rotation

(extensional faulting) occurred along the NW-SE section of the

Gamtoos Fault [pg69]. Offshore, the same tectonic stresses

produced the Gamtoos Anticline within the hanging wall and

wrench faults which in turn caused localized inversion and

rotation of fault blocks.

Thomas RJ, von

Veh MW and

McCourt S

Full paper

Journal of African

Earth Science

16 (1/2), 2-24

The tectonic evolution of

southern Africa: an overview

Keywords: Gondwana rifting,

Kaapvaal stability, tectonic

framework, crustal growth

1993 The Kaapvaal Craton showed stability around 3.0 Ga.

The Beattie Anomaly in the Cape Province is evidence of the position

of the subduction zone where the Saldania Province probably was

pulled beneath the older continental crust. This anomaly could possibly

also point to some kind of Pan-African suture zone.

The direction of deformation in the Saldania Province was toward the

northeast. Although the Cape Orogeny (Permo-Triassic) may have left

a print, there is evidence of about two deformation phases in the

Saldania province. Early N- to NE-verging folding was followed by

major thrusting in the north direction which was associated with syn-

tectonic granite intrusion. The direction of tectonic transport was

progressively toward the east.

During the Cape Orogeny, a retro-arc had foreland basin formed and

was now migrating to the northeast probably in preparation for the

deposition of the Karoo Supergroup.

The orogenic transport in the Cape was pointing toward the north.

(This orogenic belt can be traced in Australia, Antarctica and South

America).

The western branch of the Cape Fold Belt is thought to have formed

before the southern branch. This is supposed to have happened by

vertical tectonics. However, other workers argue for coeval formation of

the two deformation branches.

The break-up of Gondwana can be divided into two phases

Break-up (separation) of east and west Gondwana resulted in inversion

of thrust faults.

Rifting associated with the separation of Africa and South America at

135 Ma resulted in the development of the Agulhas-Falkland fracture

zone (east of South Africa). This rifting also caused the rotation of the

Yes The Natal sector

accommodates 3

discontinuous

tectonostratigraphic domains;

the Tugela, Mzumbe and

Margate terranes which are

part of a juvenile orogen. The

craton stabilised at about 3.0

– 2.6 Ga. reported

Mesoproterozoic intrusions

which tectonically affected

the Mzumbe and Margate

terranes. Both dextral and

sinistral strike-slip faulting is

present in the NAM zone.

Some of the structures such

as the Brakbos shear zone

were initially left-lateral and

were later reactivated as

dextral transcurrent shear

zones.

GIS_D1024_F3_Th

omas_et_al_1993.t

if

RS


68

Author1 Title

Year



SSC model?

(yes, no)


Falk Islands. The direction of the rotation was clockwise. This second

phase was ended by a regional rift-drift unconformity offshore.

However, compressional and extensional fault movement continued

into the Tertiary times.

Extensional and right lateral transtensional tectonics occurred in the

east of the SA coast.

Tectonic processes have been active from Mid-Archaean to recent

times.



69

References

Altermann, W. & Halbich, I.W. (1991). Structural history of the southwestern corner of the

Kaapvaal Craton and the adjacent Namaqua realm: new observation and reappraisal,

Precambrian Research, 52, 133- 166.

Bate, K.J. & Malan, J.A. (1992). Tectonostratigraphic evolution of Algoa, Gamtoos and Pletmos

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of the Cape Fold Belt, Karoo and Cretaceous Basins of Southern Africa. A. A. Balkema,

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Booth, P.W.K. (2009) A review of the structural geology of the Cape Fold Belt and challenges

towards future research. 11th South Africa Geophysical Association Biennial Technical meeting

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Booth P.W.K. & Shone, R.W. (2002). A review of thrust faulting in the Eastern Cape Fold Belt,

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Supergroup. Journal of African Earth Scinces, 34, 179- 190.

Booth P.W.K., Brudsdon, G. & Shone, R.W. (2004). A duplex for the eastern Cape Fold Belt:

evidence from the Palaeozoic Witteberg and Bokkeveld Groups (Cape Supergroup), near

Steytlerville, South Africa, Gondwana Research, 71 (1), 211- 222.

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exhibition, Swaziland, 481-485.

Catuneanu, O., Hancox, P.J. and Rubidge, B.S. (1998). Reciprocal flexural behaviour and

contrasting stratigraphies: a new basin development model for the Karoo retro-arc foreland

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Chevallier, L. & Woodford, A. (1999). Morpho-tectonics and mechanism of emplacement of the

dolerite rings and sill of the western Karoo, South Africa, South African Journal of Geology, 102

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Cornell, D.H., Thomas, R.J., Moen, H.F.G., Reid, D.L., Moore, J.M., Gibson. R.L. (2006). The

Namaqua-Natal Province. In: The geology of South Africa, M.R. Johnson, C.R. Anhaeusser, R.J.

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Curtis, M.L. & Hyam, D.M. (1998). Late Palaeozoic to Mesozoic structural evolution of the

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Cape Fold Belt syntaxis. Journal of Africa Earth Sciences, 21 (1), 157-169.

De Beer, C.H. (2000). Geology and tectonics of the Thyspunt site, Humansdorp. Council for


De Wit, M.J., Roering, C., Hart, R.J., Armstrong, R.A., De Ronde, C.E.J., Green, R.W.E.,

Tredoux, M., Peberdy, E., & Hart, R.A. (1992). Formation of an Archaean continent, Nature, 357,

553- 562.

Du Plessis, A.J. & Thomas, R.J., (1991). Discussion on the Beattie set of magnetic anomalies.

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Greese, P.G., Theron, J.N., Fitch, F.J. & Miller, J.A. (1992) Tectonic inversion and radiometric

resetting of the basement in the Cape Fold Belt. In: de Wit, M., Ransome, I. (eds.), pp. 217-228,

Inversion Tectonics of the Cape Fold Belt, Karoo and Cretaceous Basins of Southern Africa. A.

A. Balkema, Brookfield.



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Goedhart, M.L. & Booth, P.W.K. (2009). Early Holocene extensional tectonics in the

southeastern Cape Fold Belt, South Africa. 11th South Africa Geophysical Association Biennial

Technical meeting and exhibition, Swaziland, 510-513.

Goodland, S., Martin, A.K., & Hartnady, C.J.H. (1982). Mesozoic magnetic anomalies in the

southern Natal Valley, Nature, 295, 686- 688.

Gough, D.I. (1973). Possible linear plume under southernmost Africa. Nature, 245, 93- 94.

Halbich, I.W. (1983). A tectogenesis of the Cape Fold Belt. In: Geodynamics of the Cape Fold

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Halbich, I.W., Fitch, F.J., & Miller, J.A. (1983). Dating the Cape Orogeny. In: Geodynamics of

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(eds), pp. 149-164, Geological Society of South Africa, Johannesburg.

Hempel, C., Booth, P.W.K., Shone, R.W. & Anderson, C.R. (2004). Microstructures in thrust

zone of the Table Mountain Group (Cape Supergroup) near Laurie’sBay, Port Elizabeth, South

Africa: their use as kinematic indicators. Geoscience Africa Abstract Volume 1, 266- 267.

Jacobs, J. & Thomas, R.J. (1994). Oblique collision at about 1.1 Ga along the southern margin

of the Kaapvaal continent, southeast Africa, Geologische Rundschau, 83 (2), 322- 333.

Johnson, M.R., Van Vuuren, C.J. Visser, J.N.J, Cole, D.I., De Van Wickens, H., Christie, A.M.D.

& Roberts, D.L. (1997). The foreland basin, South Africa. In: Sedimentary basins of the world, 3:

African Basins, R.C. Selley (ed), pp. 269-317, Elsevier, Amsterdam.

Johnston, S.T. (2000). The Cape Fold Belt and Syntaxis and the rotated Falkland Islands:

dextral transpressional tectonics along the southwest margin of Gondwana, Journal of African

Earth Science, 31 (1), 1- 13.



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Johnston, S.T., McCourt, S., Bisnath, A., & Mitchell, A.A. (2003). The Tugela terrane, Natal belt:

Kibaran magmatism and tectonism along the southeast margin of the Kaapvaal Craton, South

African Journal of Geology, 106, 85- 97.

Lindeque, A. & De Wit, M.J. (2009). Revealing the Beattie magnetic anomaly and the anatomy

of the crust southernmost Africa: geophysics and deep subsurface geology where the Cape

Fold Belt and the Karoo meet. 11th South Africa Geophysical Association Biennial Technical

meeting and exhibition, Swaziland, 490-499.

Lindeque, A., De Wit, .J., Ryberg, T., Weber, M., & Chevallier., L. (2011). Deep crustal profile

across the southern Karoo basin and Beattie magnetic anomaly, South Africa: an integrated

interpretation with tectonic implications, South African Journal of Geology, 114 (3/4), 265- 292.

Lock, B.E. (1980). Flat-plate Subduction and the Cape Fold Belt of South Africa, Geology, 8,

15-8.

Matthews, P.E. (1972). Possible Precambrian obduction and plate tectonics in southeastern

Africa, Nature, 240, 37- 39.

McCarthy, T.S. & Rubidge, B. (2005). The Story of Earth and Life - a southern African

perspective on a 4-billion year journey. Struik Publishers, Cape Town, 333pp.

McCourt, S. (1995). The crustal architecture of the Kaapvaal crustal block South Africa between

305 and 2.0 Ga: A synopsis, Mineralium Deposita, 30, 89- 97.

McMillan, I.K., Brink, G.J., Broad, D.S., & Maier, J.J. (1997). Late Mesozoic sedimentary basins

off the south coast of South Africa. In: Sedimentary basins of the world, 3: African Basins, R.C.

Selley (ed), pp. 319-376, Elsevier, Amsterdam.


Sotin, C., & Galdéano, A. (2009). Simple models for the Beattie Magnetic Anomaly in South

Africa, Tectonophysics, 478, 111- 118.

Reeves, C. (2000). The geophysical mapping of Mesozoic dyke swarms in southern Africa and

their origin in the disruption of Gondwana, Journal of African Earth Sciences, 30 (3), 499- 513.



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Tankard, A., Welsink, H., Aukes, P., Newton, R. and Stettler, E. (2009). Tectonic evolution of

the Cape and Karoo basins of South Africa. Marine and Petroleum Geology, 26, 1379- 1412.

Thomas, R., Marshal, C., du Plessis, A., Fitch, F., Miller, J., von Brunn, V., & Watkeys, M.

(1992). Geological studies in southern Natal and Transkei: implications for the Cape Orogen. In:

de Wit, M., Ransome, I. (eds.), pp. 229-236, Inversion Tectonics of the Cape Fold Belt, Karoo

and Cretaceous Basins of Southern Africa. A. A. Balkema, Brookfield.

Thomas, R.J., Von Veh, M.W. & McCourt, S. (1993). The tectonic evolution of Southern Africa:

an overview, Journal of African Earth Sciences, 16 (1/2), 5- 24.

Viola, G., Kounov, A., Andreoli, M.A.G., Mattila, J. (2011). Brittle tectonic evolution along the

western margin of South Africa: More than 500 Myr of continued reactivation, Tectonophysics,

tecto-125257, 1- 22.

Weckmann, U., Branch, T. & Ritter, O. (2005). Comparing magnetic and magnetotelluric data

for the Beattie Magnetic Anomaly, South Africa. Kolloquium Elektromagnetische

Tiefenforschung, Haus Wolhldenberg, Holle, 302-306.

Weckmann, U., Ritter, O. Jung, A., Branch, T., & De Wit, M. (2007). Magnetotelluric


South Africa. Journal of Geophysical Research, 112, 1- 10.

Watkeys, M.K. (2006). Gondwana break-up: a South African perspective. In: The geology of

South Africa, M.R. Johnson, C.R. Anhaeusser, R.J. Thomas (eds.), pp. 531- 540, Geological

Society of South Africa, Johannesburg/Council for Geoscience, Pretoria.


74

Table 3.3. Data Summary Table - Seismotectonic Models and Seismic Sources (KAR, CK and NAM), Thyspunt PSHA.

Author2 Title

i

Yeari

Description and Relevance to SSC3

Is the data used

in the SSC

model? (yes, no)

Discussion of Data Use4 GIS Code

5 Originator

Seismotectonic Models

Trifonov V

Quaternary International

25, 3-12

World map of active faults

(preliminary results of studies)

Keywords: active, faults, strike-slip, normal

1995 Most continental active faults have strike-slip motion as opposed to vertical displacements. The strike slip motion is more efficient relative to thrust, reverse faults and even normal ones. This means that for a given earthquake magnitude and length of rupture, the length multiplied to give offset in a strike-slip fault would be greater than that of normal or thrusts. Strike-slip faults are grouped as rotational, translation and squeezing. The contribution of seismicity to faulting depends on the impulse creep and impulse-creep regimes of contemporary movements in the fault zones. Faults what have had offsets during the last 10k years are identified as active faults. Because of the difficulty to distinguish between Holocene geological features from those of late Pliestocene. Faults are differentiated by rate of movements, time of last activity, sense of displacement and age. The vertical component of faults offset within continents seems to be controlled by reverse or thrust motion e.g. East Africa Fault System. This shows that a major part of the continents is under compression. This paper also talks about various techniques that estimate the earthquake recurrence based on fault deformation. One of them is the use of histograms to calculate the number of earthquakes that produced a certain offset. This helps with the recurrence interval.

No RS

Clark, D., McPherson, A. And Collins, CDN.

Geoscience Australia

Record 2011/11

GeoCat# 70288

Full Report

Australia’s seismogenic neotectonic record: A case study for heterogeneous intraplate deformation.

Keywords: seismotectonic, domains, neotectonic, temporal, fault length, slip-rate

2011 Clark et al. present information about the seismogenic neotectonic deformation in the era (10-5 Ma - Miocene) for Australia. This is when the crustal stress regime occurred. This period was noted by regional-scale tilting, folding, uplifting and reverse faulting; all this related to a major unconformity in Australia. The neotectonic deformation occurred with recent stress trends which were throughout the Australian plate. Clark et al. use the 5 historic earthquakes histories and palaeoseismic data to prove that neotectonic information can be related to distinct seismogenic movements on faults. With this information, they conclude that Australia has 6 onshore neotectonic domains and 1 offshore domain. To justify their domain model, they use information on combinations/trends of properties of the crust such as length, neotectonic slip and fault densities of faults to distinguish between domains. The nature of seismicity is also considered in the domains model. This report also uses the spatial pattern of faults, interaction of fault ruptures and the size of scarps. Data on fault length can be used to estimate Mmax for each domain. Faults in Proterozoic and Palaeozoic mobile belts tend to be longer whereas faults in the centre and west of the continent report less neotectonic slip compared to the eastern part. Faults in rifted crust

Yes Cannot use the same yardstick for all SCR to distinguish seismotectonic domains.

Use of fault length and density as well as slip rate to draw the boundaries between seismotectonic domains. Using this, Mmax can be derived.

There is usually a long period of silence between earthquake (or clusters) events.

This leads to the conclusion that Australia does not have a continuing tectonic and geomorphological stability.

Three modes of neotectonic deformation at different wavelength (1000’s, 100’s and 10’s).

Larger ranges and higher values (of

GIS_S1008_F35_Clark et al_2011.tif



GIS_S1011a_F33_Clark et al_2011.tif

RS

2 Obtain from Reference Manager

3 Generic summary to be provided to Reference Manager

4 Link discussion to “Indicator of Seismic Source” table

5 GIS Code


75

Author2 Title

i

Yeari


Is the data used

in the SSC

model? (yes, no)


5 Originator

are more closely spaced relative to those in non-extended crust. Australia is a stable continental region and in the last 40 years, 5 large earthquakes occurred; correlated to hotspots of activity. SCR fault studies show that periods of earthquake activity (successive earthquakes) are separated by long quiescence periods. This could even be in the order of hundred to thousand millions of years. This may suggest that the recurrence of earthquakes is not random. There is on-going heterogeneous deformation within the Australian Plate and this is a primary response to distant plate boundary interactions. A large number of earthquakes in the historic catalogue are of moment magnitude less than 5. It is expected that this could make a small contribution to the moment budget for Australia. In Australia, 3 modes of neotectonic surface deformation are recognised in the landscape; long wavelengths (1000’s km), intermediate wavelengths (100’s km) and short wavelength (10’s km). At long wavelength there is uplift and marine erosion. This is common along the margin of Australia. At intermediate wavelengths, Late Neogene (NL) undulations of several 100’s meters parallel to those of the buckling of the lithosphere. The buckling may be associated with seismicity. However, modern seismicity is not related to lithospheric buckling. In this period (LN), subsidence of basins is also recognised. The shorter wavelength is characterised by local relief because of fault related motions. This mode of deformation is associated with seismicity. This evidence comes from comparing the ‘modern’ scarps that occurred with those of the 5 historical earthquakes. Features in the neotectonic database show long-term seismogenic record that can be used to look for information on related largest earthquake in Australia. At wavelengths greater (more than that which would cause buckling/bending), continental tilting occurs.

Apatite fission tracking and cosmogenic nuclide methods show that

Australia does not have continuing tectonic and geomorphological

stability. This is also evident in the varying rate of erosion, which is

more pronounced in high relief areas.

Mesozoic Basins and Extended Continental Crust

Because of the break-up of Gondwana, extended continental crust

developed along the margins of Australia. Mesozoic basins which

have preserved neotectonic deformation are exposed onshore

(southwest and west). Because folding is more dominant than

faulting, there is no palaeoseismic data that exists for single

earthquakes. Few fault exposures are observed but these only

seem to affect the surface Pliocene lithology. No Quaternary

fault lengths?) can indicate reactivation of mobile belts in extension during the break-up of Gondwana.

The way the crust responds to stress is used at a tool to distinguish neotectonic domains.

It is difficult to estimate the neotectonic displacement in large faults because often times the displaced dateable strata is removed by erosion.

Warning: large basin-bounding faults are often segmented. This can influence the extent of rupture. It is possible that long faults may reflect incomplete characterisation of rupture segmentation.

Vertical Displacement data (scarp size?) vary with domains. Lower displacements are a result of the amount of thicker (old/cold) crust in the old cratons and mobile belts. The larger vertical displacements (and high fault density) are because of high heat flow which makes a weaker crust.

Fault density and interaction can also be used to distinguish between domains. Fault deformation can also be used (with low confidence though) to distinguish the styles of deformation between cratonic and non-cratonic domains.

Non-cratonic domains show enhanced interaction (formation of networks) between scarps and vice versa for cratonic domains.

Scarps in non-cratonic domains are ordered in an en echelon pattern.

Fault scarp orientation can also be used to delineate domains (they also show the response of the crust to stresses). Can be randomly oriented or have a linear preferred orientation.

A common temporal pattern of active periods of a number of events (<6 events?) separated by much longer periods of inactivity.


76

Author2 Title

i

Yeari


Is the data used

in the SSC

model? (yes, no)


5 Originator

faulting history is known.

Discussions

The way the crust responds to stress is used at a tool to distinguish

neotectonic domains. But this does not really give unique results for

the domains when looking at key fault variables. It is difficult to

estimate the neotectonic displacement in large faults because often

times the displaced dateable strata is removed by erosion.

Mapping shows that large basin-bounding faults are often

segmented. Although not shown by palaeoseismological data, the

segmentation can influence the extent of rupture. It is possible that

long faults may reflect incomplete characterisation of rupture

segmentation.

Larger ranges and higher values (of fault lengths?) can indicate

reactivation of mobile belts in extension during the break-up of

Gondwana.

Vertical Displacement data (scarp size?) varies with domains.

Some domains show less displacement and some show larger

displacements. Lower displacements are a result of the amount of

thicker (old/cold) crust in the old cratons and mobile belts. The

larger vertical displacements (and high fault density) are because of

high heat flow which makes a weaker crust.

Fault density can also be used to distinguish between domains.

Fault deformation can also be used (with low confidence though) to

distinguish the styles of deformation between cratonic and non-

cratonic domains. Scarps in non-cratonic domains are ordered in an

en echelon pattern. Interaction of fault scarps also counts. Non-

cratonic domains show enhanced interaction (formation of

networks) between scarps and vice versa for cratonic domains.

Fault scarp orientation (spatial arrangements) can also be used to

delineate domains (they also show the response of the crust to

stresses). Can be randomly oriented or have a linear preferred

orientation.

A common temporal pattern of active periods of a number of events

(<6 events?) separated by much longer periods of inactivity. This

This affects the slip rate (which will change over time). The inter-seismic interval can be in the order of 20-40k years.


77

Author2 Title

i

Yeari


Is the data used

in the SSC

model? (yes, no)


5 Originator

affects the sip rate (which will change over time). The inter-seismic

interval can be in the order of 20-40k years.

Implications

Intraplate fault characters are not universal when applied to SCR

analogues.

Extended crust (reactivated Proterozoic fold belts and Palaeozoic

fold belts) has more seismicity relative to non-extended crust. In

terms of the amount of slip, Palaeozoic fold belts are more active

than Proterozoic fold belts.

Here they make the point that in other SCR like North America,

there are cores (stable blocks) which are fringed by orogenic belts

(This is also the case in south Africa).

Singh, M. Kijko, A. and Durrheim, R.

Natural Hazards,

First-order regional seismotectonic model for South Africa

Keywords: seismotectonic, model, domains, seismogenic, faults, clusters

2011 First order seismotectonic model for South Africa was done by incorporating geoscientific data. Characterisation, assimilation and zonation were implemented. The use of earthquake foci and neotectonic information, seismotectonic domains, systems and structures became. From the work of Fouche (2004), mantle structures follow the surface geology across the craton. A thick mantle keel is seen beneath the Kaapvaal craton (the crust is thin though) and a slightly smaller keel is seen beneath the Limpopo mobile belt (also characterised by a thick crust and complex Moho). Low mantle velocities are observed below the Bushveld Complex (crust thick and Moho complex). The crust beneath the NMMB is thick with a complex Moho. This paper also mentions seismogenic faults that are related to seismicity and those that could be (epicentres are close to the fault but there is no evidence of the link). Some faults are tectonically active but are not related to any known seismic event and others are related to seismicity. Most earthquakes (shown to be in a space similar to what could be called CKN zone) do not have any known sources. Others outside this zone can be related to mining activities, CFB, Ceres cluster, CT clusters. Tectonic indicators are used to determine stress orientations. Earthquake clusters can either show strike-slip or normal faulting regimes (e.g. Koffiefontein cluster – northwest-SE compressive stress orientation). In the NMMB, orientations vary from northwest-SE to east-west. This anisotropy implies a pattern of ancient mantle lithospheric deformation beneath South Africa. Singh et al. Define seismogenic domains as units that show distributed seismicity which cannot be assigned to specific geological structures (see Davis, 2002). Large structural domains had no influence on seismotectonic zonation because many neotectonic domains transect structural domains. Earthquake clusters with no association to large faults or neotectonic activity form seismogenic domains.

Yes The Griqualand-Transvaal axis runs across the NAM zone in a northeast-southwest direction. The axis is related to the subsidence of the Kalahari basin (Partridge, quoted in Singh et al. 2009). Low levels of seismicity are observed along this axis.

GIS_S1016a_F7_Singh_et_al_20011.tif

GIS_S1016b_F7_Singh_et_al_20011.bmp

RS


78

Author2 Title

i

Yeari


Is the data used

in the SSC

model? (yes, no)


5 Originator

They also use the likelihood method to assess the b values. Some seismotectonic zones have high b values and high seismicity. Other zones have low b values but high seismicity (e.g. Ceres zone). Koffiefontein has similar b values but is less active w.r.t. the Ceres zone. b values for other zones could not be calculated because of insufficient seismicity data. The b values vary from 0.57 to 0.8 on the CKN zone. The perspective of Singh et al. suggests that seismotectonic model transects the boundaries of structural domains. The Ceres, Koffiefontein and CSA (Ciskei, Swaziland Axis) domains are characterised by naturally occurring earthquakes. The Griqualand-Transvaal axis runs across the NAM zone in a northeast-southwest direction. The axis is related to the subsidence of the Kalahari basin (Partridge, quoted in Singh et al. 2009). Singh et al. (2011) suggested low levels of seismicity along this axis.

Singh, M. Kijko, A. and Durrheim, R.

Full Paper

Seismological Research Letters

80(1), 71-80

Seismotectonic Models for South Africa: synthesis of geoscientific information, problems and the way forward

Keywords: seismicity, clusters

2009 This paper points out the need to do further studies to gather information on both geology (quaternary neotectonics) and seismology (network expansion, separate mining and natural earthquakes, depths and focal mechanism) in order to create a seismotectonic model for South Africa. A better and denser monitoring network is also essential. This paper also identifies several seismicity clusters some of which are a result of mining related activities. The famous 1969 and 1912 earthquakes are located in the Ceres and Koffiefontein clusters respectively. The largest earthquake occurred in Cape Town in 1809. There is a greater concentration of seismicity along the Great Escarpment in South Africa. To be able to identify whether earthquakes originated in the Karoo, Natal-Namaqua belt of the Kaapvaal Craton, it is important to include a depth parameter when reporting earthquakes taking into consideration that the Karoo is the large geological entity in South Africa. The sparsity of seismicity in South Africa cannot be easily linked to geological provinces. The Beattie anomaly and the South Cape Conductive Belt show no correlation to seismicity in the region. In the south-western part of South Africa, an east-west horizontal stress regime exists consisting of compressional forces coming from the Mid-Atlantic Ridge. To prove this, strike-slip faulting is observed along main east-west trending fracture systems. (This is different to the EAR where the principal stresses are in the vertical direction (producing normal faulting) due to the swell-push from the upwelling of the asthenosphere and the thinning of the lithosphere). The African Superswell is placed between these two zones.

Yes The Griqualand-Transvaal axis runs across the NAM zone in a northeast-southwest direction. The axis is related to the subsidence of the Kalahari basin (Partridge, quoted in Singh et al. 2009). Singh et al. (2011) suggested low levels of seismicity along this axis.

RS

Brandt M.

CGS Internal Report

2008-0001

A review of the seismotectonic provinces and major structures in South Africa, with new data

Keywrods: seismotectonic, models, superswell

2008 This paper discusses and summarises seismotectonic models by Hartnady (1996), Du Plessis (1996) and Partridge (1995). With the new seismic tomography data, the African superswell/ superplume beneath Eastern and Southern Africa has been confirmed and mapped in detail. The new magnetic data from the Southwestern Indian Ridge show slow deformation over a zone of 100km width. The rift system (EARS) along the Nubian-Somalian boundary does

No RS


79

Author2 Title

i

Yeari


Is the data used

in the SSC

model? (yes, no)


5 Originator

not extend into South Africa. This according to new seismic tomography data. In fact, this rift system is observed to be diverted toward the coast of Mozambique. Opposed to what is published in the World Stress Map, the compression directions from two seismic stations are east-northeast to west-southwest and north-south.

Partridge, TC

CGS Internal Report

A review of existing data on neotectonics and palaeoseismicity to assist in the assessment of seismic hazard at possible nuclear power station sites in South Africa.

Keywords: seismotectonic, seismic, zone

1995 In this report, Partridge advocates two broad areas in Southern Africa; the southwestern and northeastern (where the East African rift is which is dominated by swell-push generated by upwelling of asthenospheric material and thinning of the lithosphere. Here, whilst capable fault are identified, the East African Rift is proposed to extend into South Africa along seismically active zones from Mpumalanga to the Zambezi River catchment and from the Mozambique channel passing through northern Natal and to the west coast. Relying on the seismogenic mechanisms and previous seismicity levels, 6 seismotectonic provinces are identified. Of these, the most active is a broad zone along the east coast beginning east of Port Elizabeth. The central Bushveld basin zone experienced reactivation in the late Neogene. In this zone, the seismicity is related to the basin movements and marginal faults. The southern zone that encompasses the Cape Fold belt is characterised by a few east-west trending capable faults and east-west maximum principal stresses. Partridge has identified more than 8 capable or potentially capable faults. Three of these are included in the southern zone (Thyspunt is within this zone) and most of them are thought to have resulted from tension stresses due to Gondwana rifting and have undergone episodic reactivation. The faults in the east-west trending Cedarville/Koffiefontein/O’kiep seismic zone have not been published as capable but recent studies show that they may have been active. In this zone, an east-west zone of decollement which meets the Moho at 300km to the south.

Yes The different zones in Partridge’s model are compared to the zones demarcated for the SSHAC 3 seismic source model.

GIS_M1015a_F(Map1)_Patridge_1995.tif

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Hartnady, CJH

CGS Internal Report

Seismotectonic Provinces of South Africa: Critical review and new proposals

Keywords: zone, microplate, seismotectonic

1996 This paper proposed that Southern Africa is a wide plate boundary zone extending from the East African Rift System to the south of Africa and not an intraplate region. The paper also suggests that within this wide zone, there are aseismic microplates which are surrounded by seismic mobile belts. Two types of seismotectonic provinces are discussed in this report; microplates and mobile belts around them. For Southern Africa, Hartnady identified 3 microplates and 7 mobile belts. In the South African context, there are 2 microplates (Spesbona and Transgariep) and 3 mobile belts (Mpumalanga, Cedarville/Ulwandle and Oranje Belts). The microplates show sparse seismicity. The mobile belts show diffuse seismicity which is more pronounced that in the microplates. Hartnady also states that Southern Africa has finally been classified as a broad zone of crustal deformation which includes the boundary between the Nubian and Somalian plate.

Yes The different zones in Hartnady’s model are compared to the zones demarcated for the SSHAC 3 seismic source model.

GIS_M1013a_F1_Hartnady_1996.tif

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Du Plessis, A Seismicity in South Africa and its relationship to the geology of the

1996 Du Plessis (report written for nuclear site selection) here also compares his model to that of Partridge (1995) and Hartnady

Yes The different zones in Du Plessis’ model are compared to the zones

GIS_M1012a_F11_Du Plessis_1996.tif

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CGS Internal Report

1996-0019

region

Keywords: earthquake, seismogenic, zones, clusters, tectonic

(1996). Du Plessis’ seismotectonic model is used to characterise type frequency/magnitude relationship of earthquake events that affect the study area. This model suggests that there are two element types; 1. Seismogenic structures that match the available data (geological, geophysical, geomorphological, seismological); 2. And those that cannot be correlated to specific structures. There is a distinctive pattern of seismicity in SA. Du Plessis reports that earthquake epicentres can be correlated to discrete geological structures. Although the activity north (EAR) of South African can be explained by rifting, there is no evidence of the same activity also affecting the geology in South Africa. The northeast (Mpumalanga, northern Natal and Swaziland) and the western (Namibia) zones are parallel to the original lines along which the Gondwana broke. The southern zone is parallel to the Namaqua- Natal metamorphic province; south of the Kaapvaal craton. Five seismicity zones are identified in South Africa. Of these, the Free State-Lesotho-Natal zone is the most seismically active and contains 3 distinct clusters. Some of these clusters may be linked to isostatic readjustments of the eroding crust and others associated with high gravity anomalies. So far, 2 of the 5 zones show low tectonic seismicity (central South African and the Cape). The central South African is situated within the Kaapvaal Craton. The only active clusters are those created by mine seismicity in the central South African zone and the Ceres cluster in the Cape zone.

demarcated for the SSHAC 3 seismic source model. The CK and the NAM are similar to the Free State/ Lesotho/Natal and the Karoo/Namaqua respectively.

Tankard A., Welsink, H, Aukes, P, Newton R and Stettler E.

Full paper

Marine and Petroleum Geology, 26

1379-1412

Tectonic evolution of the Cape and Karoo basins of South Africa

Keywords: Cape Orogeny, intraplate tectonics, mantle flow, Karoo,

2009 Subsidence (represented by the Karoo and Cape basins) is a product of lithospheric deflection because of mantle flow plus long distant subduction. The two basins have undergone crustal uplift, lengthy regional subsidence and subsidence controlled by first order basement faults [pg1380]. Two large-scale episodes of intermittent subsidence are well represented by the Cape and Karoo basins.

In contrast to Johnston (2000), suggesting that the Falklands Plateau has not been rotated, Tankard et el. argue that there is no seismic evidence of microplate boundaries and that the time interval (from

40Ar/

39Ar dating) for this is too short for this kind of rotation

[pg1381]. The southern edge of the Namaqua crustal block is interpreted as a volcanic rift margin with a Wnorthwest orientation and a thick crust. The Namaqua thrust front has a 9° down-to-the-north dip and has vertically displaced the Moho by 14km [pg1385].

Deep burial studies by Rowsell and de Swardt, 1976) suggest an 8 km of uplift and erosion. The southern margin of the Namaqua plate (intraplate suture zone) is typical of N-dipping shallow crustal fault displacing the Moho. Basin formation and deformation is controlled by the reactivation of this suture zone [pg1386].

Large-scale subsidence continued in the Devonian but not

Yes Cape Orogeny is up to 250-215 Ma.

The Karoo and Cape basins have been crustally uplifted. Basement faults controlled the long periods of regional and subsequent subsidence in the two basins. These authors also suggest that subsidence was controlled by mantle flow.

Formation and deformation of these basins are a result of the reactivation of the Namaqua suture zone (Thrust in the Namaqualand regions has displaced the Moho by 14 km).

Both thick and thin-skinned models are used for Cape Orogeny. In contrast to Johnston (2000), the CFB is thought to be a right-lateral

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accommodated by faulting. [pg1390]. The Cape Fold Belt is mostly thick-skinned (strike-slip orogen) but the foreland edge is thin-skinned. There are two main subsidence and deposition events in the Karoo basin, separated by a hiatus of 10 Ma. Burial studies show a 3 km uplift and erosion north of the CFB.

In the Permian times, before the Cape orogeny the early Karoo basin was subjected to subsidence by vertical displacement of rigid basement block decoupled along the crustal-scale boundary faults [pg1397]. Although the individual blocks responded in different ways, subsidence was primarily controlled by mantle flow. Some strike-slip faults in the Karoo basin have been activated by older displaced principal shear zones. This subsidence was terminated by regional left-lateral strain (including the CFB and Hartbees-Doringberg shear zones) [pg 1407].

Based on the en echelon faults, folds, flower structures and uplift along the Worcester Fault, the Cape fold belt is a sinistral strike-slip belt (of Worcester and Cango shear zones) due to the Saldanian orogenic event and is linked to the reactivation of the Namaqua suture (which became a plane of detachment). The Karoo is classified as a transtensional foreland basin that is thought to be a result of the boundary forces associated with the Cape Fold Belt and the en echelon fault zones [pg1408].

belt.

Namaqua Seismic Source Zone

Viola, G, Kounov, A, Andreoli, MAG and Mattila, J

Journal of Structural Geology

28, 868-886

Influence of crustal heterogeneity on normal fault dimensions and evolution: southern South Africa extensional system

Keywords: extensional, compression, faults, Mesozoic

2011 Mesozoic extensional system is superimposed on a Palaeozoic heterogeneous lithosphere. About 78 to 230km long fault arrays are within this system (which is more than 480km long). These faults show displacements of up to 16 km; they are the longest and show the largest throws. These faults are also high-angle (45 to 60°) normal faults. In contrast to other extensional systems, this one has faults that are co-linear segments rather than en-echelon segments and this is because of the structural inheritance between the underlying Cape Fold Belt and the resultant extensional system. The displacement on faults in the extensional system is dependent on the underlying compressional faults. These resultant faults are parallel to the underlying compressional faults. The growth of these faults was then achieved within the 6 Myr of rift initiation way before they could displace. There is no evidence of intra-basin faults. Structures formed from the extensional system are parallel to the underlying compressional faults and also reactivate them. Stress studies in today’s conditions indicate that the west-northwest to east-southeast and north-northwest to south-southeast striking faults are under critical stress and may be reactivated in future. (Steep strike-slip faulting formed during the amalgamation of Gondwana (related to the opening of the Atlantic Ocean) when the Gariep belt collided with the rigid and thick Namaqualand crust/foreland. This happened in the Neoproterozoic Pan African orogeny)

Yes This information gives a good basis to demarcate this region (western South Africa) with younger extension from the one to the east mostly with Proterozoic structures. This demarcation is where the source boundary is.

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McCarthy, TS and Rubidge, B

Struik Publishers, Cape Town, 333pp.

The Story of Earth and Life - a southern African perspective on a 4-billion year journey

2005 The Griqualand-Transvaal axis is one of the three swells unique to Africa. The axis runs across the NAM zone in a northeast-southwest direction. Uplift occurred along this axis and also affected the river networks of South Africa. Slight movements along this axis led to the disruption of drainage networks and resulted in new networks

Yes The Griqualand-Transvaal axis runs across the NAM zone in a northeast-southwest direction. Slight movements along this axis led to the disruption of drainage networks and resulted in new networks.

RS

Altermann W and Halbich IW

Precambrian Research

52

133-166

Structural history of the southwestern corner of the Kaapvaal craton and the adjacent Namaqua realm: new observations and a reappraisal

Keywords: structures, faults, deformation, margin, Kaapvaal

Seen as far as 130 km away from the modern margin of the craton, duplication/thickening of the Transvaal Supergroup along the southwestern margin of the Kaapvaal craton (Griqualand West) by complex thrusting and folding is observed. Up to seven tectonic events deformed the rocks along the southwestern margin of the Kaapvaal craton. One of the results is the main northwest structures (specifically produced by D5). The Doringberg-Hartbees fault zone was produced by D7. One of the oldest deformations is in the north-south trending Uitkomst cataclastics of the pre-Makganyene age and interpreted at bedding-parallel thrust.

Other major structures include the Brakbos and the Brakfontein shear zones. These are truncated at the Doringberg-Hartbees fault zone; an oblique left-lateral wrench. The last movement along the Doringberg-Hartbees fault; the margin of the Kaapvaal Craton was at about 1.0 Ga, after the collision of the Kaapvaal craton and the Namaqua-Natal mobile melt. Dip angles ranging from 70° to 80° toward the southwest direction for some of the transcurrent thrusts. The Doringberg fault is possibly a place along which the Archaean granites were juxtaposed against the Early Proterozoic Campbell Rand subgroup of the Ghaap Group.

Structure within the seven episode deformation include imbricates and recumbent fold zones, gravity slumps and tectonic decollements, thrusts and folds, (and lineaments interpreted from aeromagnetic data), and right-lateral faults.

Yes Other major structures include the Brakbos and the Brakfontein shear zones. These are truncated at the Doringberg-Hartbees fault zone. There are several deformation episodes in the NAM zone resulted in the main northwest structures (specifically produced by D5). The Doringberg-Hartbees fault zone was produced by D7. The last movement along the Doringberg-Hartbees fault; the margin of the Kaapvaal Craton was at about 1.0 Ga, after the collision of the Kaapvaal craton and the Namaqua-Natal mobile melt. Most faults in the NAM zone have steep to sub-vertical dip angles toward the easterly direction. Dip angles ranging from 70° to 80° toward the southwest direction for some of the transcurrent thrusts have been reported

GIS_X1025_F1_Altermann_and_Halbich_1991.bmp

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Cornell DH, Thomas, RJ, Moen HFG, Reid, DI, Moore, JM and Gibson RL

The geology of South Africa (Johnson, Anhaeusser and Thomas: eds)

531- 540,

The Namaqua-Natal Province

Keywords: tectonostratigraphic, orogen, sector, subduction, convergence

2006 The tectonostratigraphic Namaqua-Natal province is situated along the western and southern margin of the Kaapvaal craton. The rocks formed during the Namaqua orogen at about 1.2 Ga to 1 Ga. The rocks are exposed in the Northern Cape and the Kwa-Zulu Natal Provinces. Geophysical data show that there is continuity joining the two sectors. In the Northern Cape, the western Namaqua sector is separated from the Kaapvaal craton by the Kheis belt. The northern part of the Namaqua sector is characterised by folds and thrusts. Five subdomains are recognised in the Namaqua sector showing a range of rocks with varied grades of metamorphism and ages (from 2.0 to 1.3 Ga).

The early evolution of the Namaqua Natal metamorphic Belt is linked with the Kheisian events (between 2.0 and 1.6 Ga). Rifting and ocean basin development are reported in the Namaqua. The rifting gave rise to extensional intracratonic basins in which supracrustal sequences were deposited. Back-arc basins also developed in the Kaapvaal-Kheis passive continental margin. After the rifting phase. The Namaqua-Natal sectors also record

Yes Only used figure showing the Natal sector.

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prolonged southwest-northeast plate convergence that led to subduction of the Tugela-Areachap ocean and growth of volcanic arcs between 1.3 and 1.2 Ga. Collisions in both sectors caused intense medium to high grade metamorphism, deep crustal melting and the production of large volumes of granitoid magmas.

Stowe CW

Namaqualand Metamorphic Complex (Botha BJV, ed)

Special publication 10

147-172

The Upington geotraverse and its implications for craton margin tectonics

Keywords: transcurrent, dextral, shear, sinistral,

1983 The Namaqua front; a strongly positive feature and arched by differential movements is a transcurrent zone of northwest trending shears and elongate granite plutons. Major northwest trending shear zones and north-northwest trending fault zones are associated with the Doringberg lineament in the east of the Namaqua sector. The Hartbees fault zone displaces earlier ductile shear zones. The Doringberg fault zone extends about 180 km northeast from the Brakbos fault and splays northward in to other faults. The sense of movement along the Doringberg was dextral and displacement was about 139 km. At a later time, sinistral displacements of about 7 km occurred in the southwest (290°) direction. The Doringberg lineament marks the eastern boundary of the Namaqua Province and is buried beneath the Karoo cover.

No RS

Stowe CW

Transactions of the Geological Society of South Africa, 89, 185-189.

Synthesis and interpretation of structures along the north-eastern boundary of the Namaqua tectonic province. South Africa,

1986 The transcurrent shear and fault zones in the Namaqua Province are about 1.1 Ga in age. The Namaqua front represents a ‘new’ continental crust that was accreted during the Namaqua orogeny. The first deformation event in the Namaqua province included overthrusting (and F1 folding)

Yes The sixth (D6) and seventh (D7) deformation episodes produced interference folding and the Doringberg-Hartbees fault zone respectively. D6 folding is dated at about 1.1 Ga.

RS

Janney PE, Shirey SB, Carlson RW, Pearson DG, Bell DR, Le Roux AP, Ishikawa A, Nixon PH and Boyd FR

Journal of Petrology, 51 (9)

1849-1890

Age, composition and thermal characteristics of South Africa off-craton mantle lithosphere: evidence for a multi-stage history

Keywords: Namaquan, orogeny, ages, xenoliths, mantle

2010 Re-Os model ages and mineral chemistry indicate that the Namaqua-Natal mobile belt (Greenville age) stabilised within a few hundred years following the Archaean. The Namaquan Orogeny occurred between 1.3 and 1.0 Ga and may have been accompanied by widespread partial melt extraction. In contrast to other authors, here the Namaqua crust is regarded as warmer (at a given pressure) and thinner than the adjacent Kaapvaal craton. The characteristics appear to have started only in the Mesozoic. From the off-craton mantle xenoliths, there is evidence of a Mesozoic heating episode most probably brought by mantle swelling linked to continental break-up and or Karoo flood basalt magmatism.

Yes Using Re-Os model ages and mineral chemistry, this Greenville age mobile belt stabilised within a few hundred years following the Archaean. The Namaquan Orogeny occurred between 1.3 and 1.0 Ga.

RS

CK Seismic Source Zone

Goodland SW, Martin AK and Hartnady CJH

Nature 295

686-688

Mesozoic magnetic anomalies in the Southern Natal Valley

Keywords: magnetic, anomaly, Falkland, fracture zone,

1982 This paper discusses the use of magnetic geophysical data to determine the movement between the Falkland Islands and Africa. Using this information, the Falkland Island could be rotated back (by reconstruction of West Gondwanaland) into the Natal Valley. This is a region between SE Africa and the Mozambique Ridge. The movement was constricted by the orientation of the Agulhas Falkland Fracture Zone along which the Falkland Plateau moved past. These authors proposed that there was an average of 15cm/yr of Mesozoic half-spreading rate in the Natal Valley.

Yes The Agulhas Falkland Fracture Zone is a good feature to be used as the eastern boundary of the CK zone.

RS

Brandt MBC and Saunders I

Seismological

New regional moment tensors in South Africa

2011 For areas like South Africa with relatively low seismicity, regional moment tensors provide indicators for seismotectonic and hazard studies. Added to the sparse distribution of broadband

Yes Faulting regime in South Africa changes from normal faulting in the northeast (close to the East Africa

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Research letters 82 (1)

69-80

Keywords: seismicity, focal, mechanism, faulting, strike-slip, normal, moments, tensors

seismometers (in the South African National Seismograph Network), the low seismicity is the cause of few regional moment tensors in South Africa. Information from both tectonic and mine related seismicity is used here. From the focal mechanism solutions, the faulting regime in South African can be deduced to transform from normal faulting in the northeast (interpreted as a result of crustal stresses associated with uplift and rifting) to strike-slip faulting in the southwest (resulting from ridge pushes from surrounding plate boundaries and/or local crustal thicknesses).

Rift). The changeover is somewhere in the CK zone where the assumption of strike-slip faulting begins and toward the southwest of South Africa (Syntaxis zone).

De Wit MJ, Roering C, Hart RJ, Armstrong RA, De Ronde CEJ, Green RWE, Tredoux M, Peberdy E and Hart RA

Nature 357

553-562

Formation of an Archaean continent

Keywords: Kaapvaal, craton, lineament, suture, amalgamation, subdomains

1992 The Kaapvaal craton is one of the only two preserved significant portions of the relatively pristine mid-Archaean rocks (continental fragments) in the world. The craton formed and stabilised between 3.7 and 2.7 Ga. This means that the tectonic history of the craton span 1 Ga. This can be divided into 2 periods; the first period record the initial separation of the continental lithosphere of the craton from the mantle = craton shield formation. The second period marks the formation of the craton proper. This period is associated with intra-continental and continental-margin – continental growth by tectonic accretion of fragments and subduction-related processes. The craton consist of a mosaic of subdomains that were amalgamated together by plate tectonic processes.

The Colesberg lineament is shown in this paper as the north-south region along which the Mid-Archaean and the Late Archaean subdomains were sutured. The western and eastern subdomains on either side of the Colesberg lineament have north-south and northeast-southwest structural domains.

Yes The Colesberg lineament is a region along which the subdomains of the Kaapvaal craton were sutured.

RS

Lana C, Gibson RL, Kisters AFM and Reimold WU

Earth and Planetary Science Letters 206

133-144

Archaean crustal structure of the Kaapvaal craton, South Africa – evidence from the Vredefort dome

Keywords: Vredefort dome, Kaapvaal, stabilisation,

2003

The tectonometamorphic (polyphase deformation) history and high-grade regional metamorphism as well as anatexis found in the Vredefort impact structure may indicate the final stages of the consolidation of the Kaapvaal craton and stabilisation of its lithospheric root before the development of major volcanic and sedimentary basins. The tectonism along the Colesberg lineament is related to lateral accretion of Late Archaean volcanic arcs on to the main cratonic mass. The Kaapvaal craton grew and was modified by subduction-accretion processes between 3.1 and 3.6 Ga.

No RS

De Wit M and Tinker J

South African Journal of Geology 107 (1/2)

185-206

Crustal structures across the central Kaapvaal craton from deep-seismic reflection data

Keywords: Kaapvaal, craton, amalgamation

2004 The Colesberg magnetic lineament (CML) does not define a simple Archaean structure. It divides the Kaapvaal craton into two eastern and western domains. In contrasts to other who regard the CML as an underlying suture in the lower crust and mantle, here is shallow and may be related to either Archaean greenstone belts or possible back-thrust of magnetic shale wedges. Seismic data confirm that the Kaapvaal craton is overthrust by the Namaqua-Natal mobile belt. The cratonic crust and probably the mantle lithosphere underlie the large portion of the NNMB beneath Natal and Eastern Cape regions. There are sharp shallow-dipping structural planes that subdivide the Kaapvaal craton causing a resemblance of tectonically stacked series of crustal panels derived from the Neoarchaean.

Yes The Colesberg-(Trompsburg) fault zone is a Neoarchaean palaeosuture.

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McCourt S

Mineralium Deposita 30

89-97

The crustal architecture of the Kaapvaal crustal block, South Africa between 3.5 and 2.0 Ga: A synopsis

Keywords: tectonostratigraphic, Kaapvaal, continental, collision

1995 The southern and central tectonostratigraphic subdomains of the Kaapvaal Craton became a solid unit by 3.1 Ga. The central part of the craton underwent extension to accommodate several major sedimentary basins in South Africa including the Witwatersrand and the Ventersdorp basins. This is during the collision of the Zimbabwe craton and the Kaapvaal craton causing the development of the accretionary Limpopo belt. The main structural grain on the Kaapvaal craton is east-northeast. This is seen in the orientation of the major greenstone belts on the craton (and also in the orientation of the thrust faults and shear zones in the CK zone). The structural grain in the southwestern part of the craton is in the northerly direction. The Late Archaean evolution of the Kaapvaal craton was governed by continental margin tectonics that were associated with collisional orogeny around the northern and western margins of the Kaapvaal shield.

Yes The Kaapvaal craton underwent various tectonic evolutionary episodes, leaving appreciable evidence for collision with the adjacent Zimbabwe craton and the Namaqua-Natal mobile belt and extension to accommodate various sedimentary basins and complexes

RS

James DE, Nui F and Rokosky J

Lithos 71

413-429

Crustal Structure of the Kaapvaal craton and its significance for early crustal evolution

Keywords: Moho, accretion, tectonomagmatic,

2003 Near Kimberly (West of Kaapvaal craton), the crust of the Kaapvaal craton is about 35 km thick and the topography of the Mohorovicic discontinuity is flat and sharp. The structures observed in the Moho beneath the region formed by accretionary processes (e.g. Limpopo Belt) which were produced by reworking during subsequent tectonomagmatic events, are absent under the undisturbed Kaapvaal craton. The uniform (flat and sharp) Moho may have resulted from thermal reactivation and large volume melting of the cratonic crust in the Late Archaean. Another mechanism causing this flattening may be regional detachment at the Moho. Layering related to the crystallisation of melt in the lower crust is another plausible means for producing a flat and sharp Moho. The density contrast across the Moho revealed that the lower crust beneath cratons in southern Africa is felsic to intermediate. Analysis of waveform broadening of the crustal reverberation crustal phases suggests that the Moho transition is about is no more than 0.5 km thick and the crustal thickness variation across as area of 2400 km

2

is less than 1 km.

Yes The crust of the Kaapvaal craton is about 35 km thick and the topography of the Mohorovicic discontinuity is flat and sharp.

RS

Corner B, Durrheim RJ and Nicolaysen LO

Tectonophysics 171

49-61

Relationship between the Vredefort structure and the Witwatersrand basin within the tectonic framework of the Kaapvaal craton as interpreted from regional gravity and aeromagnetic data

Keywords: Colesberg, downwarp

1990 The Colesberg magnetic anomaly is related to the Vredefort (largest and well preserved impact structure in Africa) discontinuity and also marks the western margin of the Witwatersrand basin. The anomaly may be a manifestation of magnetite enrichment within the midcrust. It is also interpreted as a north-trending fault arc. The Colesberg lineament corresponds to an axis of crustal downwarp formed before the Vredefort structure and the Johannesburg dome.

Yes The anomaly may be a manifestation of magnetite enrichment within the midcrust.

RS

Marshall, CGA

The geology of South Africa (Johnson, Anhaeusser, and Thomas: eds.)

433- 442,

The Natal Group

Keywords: Pan-African, orogeny, graben, Natal trough

2006 The Natal Group was earlier considered to be part of the Cape Table Mountain Group but research has shown this to be improbable. The Natal Group sediments were most probably derived from the Pan-African orogenic belt in the southern part of Mozambique and deposited in the Natal Trough. The Natal Group was deposited in the Natal Trough representing a graben parallel to the coast of KwaZulu Natal. The Natal trough or graben is truncated to the east by the Agulhas Fracture Fault Zone and only the western portion is preserved along the east coast as the eastern

Yes The Natal Group was deposited in the Natal Trough representing a graben parallel to the coast of KwaZulu Natal. The Natal trough or graben is truncated to the east by the Agulhas Fracture Fault Zone and only the western portion is preserved along the east coast as the eastern portion was removed

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portion was removed during the break-up of the Gondwanaland. during the break-up of the Gondwanaland.

Wright C, Kwadiba MTO, Simon RE, Kgaswane EM and Nguuri TK

Earth Planets Space 56, 125-137

Variations in the thickness of the crust of the Kaapvaal craton and mantle structure below southern Africa

Keywords: Kaapvaal, thickness,

2004 The estimated the thickness of the southern Kaapvaal craton to be about 38 km which was lower than the 50 km estimated for the northern part of the Kaapvaal craton. The area affected by the Bushveld intrusion shows the much thicker crust. The Pn and Sn times show that the crust in the northern regions of the craton is about 7 km thicker on average than values estimated from receiver functions. This may be attributed to the variation in the elastic properties in the mafic rocks that form the lower crust which can also change considerably depending on the metamorphic grade and small changes in composition. In the southern part of the craton, receiver functions indicate a sharp crust-mantle boundary.

Yes The crust in the north of the Kaapvaal craton is thicker (about 50 km) than the crust in the southern part of the craton (38 km).

RS

Catuneanu, O, Hancox, PJ and Rubidge, BS

Basin Research, 10,

417- 439.

Reciprocal flexural behaviour and contrasting stratigraphies: a new basin development model for the Karoo retro-arc foreland system, South Africa

Keywords: orogenic, loading, unloading, compression

1998 The orogenic cycles of loading and unloading (see Halbich 1983) in the Cape Fold Belt controlled the sedimentation of the Karoo Foreland Basin. The belt is part of the Pan Gondwanian mobile belt formed through compression, collision and terrane accretion along the southern margin of Gondwanaland. The tectonism of the Cape Fold Belt started with compression including thrusting and folding in the Late Carboniferous to Middle Triassic, proceeded with orogenic relaxation and ended at the start of the rifting of Gondwanaland in Middle Jurassic

Yes The tectonism of the Cape Fold Belt started with compression including thrusting and folding in the Late Carboniferous to Middle Triassic, proceeded with orogenic relaxation and ended at the start of the rifting of Gondwanaland in Middle Jurassic. The surface geology in the KAR zone is of the Karoo Supergroup whose deposition was influenced by the tectonism in the Cape Fold Belt which included compression and relaxation of the Cape orogeny

RS

Cornell DH, Thomas, RJ, Moen HFG, Reid, DI, Moore, JM and Gibson RL

The geology of South Africa (Johnson, Anhaeusser and Thomas: eds)

531- 540,

The Namaqua-Natal Province

Keywords: tectonostratigraphic, obduction, Kaapvaal

2006 The Natal sector in the Kwa-Zulu Natal Province can be divided into three tectonostratigraphic domains and can be correlated with the Namaqua sector in the Northern Cape Province. In the Natal sector, there is evidence of obduction of the Tugela terrane; one of the tectonostratigraphic domains, onto the Kaapvaal craton. The Natal sector is also typified by granite intrusions in the Mzumbe and Margate terranes (two of the tectonostratigraphic domains).

The Natal sectors is also typified by shear zones and thrusts observed in the tectonostratigraphic domains of the sector.

Yes Used Figure Only GIS_S1006_F28_Cornell_et_al_2006.tif

RS

Jacobs J and Thomas RJ

Geologische Rundschau 83 (2)

322-333

Oblique collision at about 1.1 Ga along the southern margin of the Kaapvaal continent, south east Africa

Keywords: obduction, collision, tectonostratigraphic, oblique

1994 The 1.1 Ga Namaqua-Natal mobile belt or the Natal Metamorphic province collided with the Kaapvaal craton at an angle. The Natal Metamorphic province (NMP) is regarded as a Mesoproterozoic ocean arc which collided obliquely with the Kaapvaal craton. This Greenville age mobile belt is host to three tectonostratigraphic domains in the Natal area. These show evidence of prolonged northeast-southwest plate convergence (early thrust tectonics and sinistral transcurrent shearing). This direction was at an angle to the approximately east-west orientation of the pre-existing cratonic foreland. The result was the stacking of the tectonostratigraphic terranes (in the Natal area) which are characterised by low angle structures and northeast verging recumbent folds and younger subvertical shear fabrics and subhorizontal to oblique lineations and

Yes The Kaapvaal Craton collided with the Namaqua-Natal mobile belt obliquely at 1.1 Ga. The Proterozoic structures in the NAM zone are mostly low angle northwest-trending thrusts and almost vertical shear zones. .

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folding near vertical axes. Subhorizontal compressional tectonics resulted in the thickening of the crust followed by oblique transcurrent shearing within the transport regime. There are three tectonostratigraphic terranes; Tugela, Mzumbe and Margate. The NMP is subdivided into domains with shallow southerly dipping and near-vertical fabrics. The Tugela terrane is dominated by thrust tectonics whereas the Mzumbe and the Margate terranes are dominated by large scale wrench movements. Previous thrust structures have been mostly obliterated by these movements but some parts are preserved in the Tugela terrane. Around 1.025 Ga, the northeast-southwest plate convergence had largely stopped and this is marked by the emplacement of high level crust microganulitic dykes into the brittle but stabilised crust.

Early phase thrusting displays dips angles ranging from 10-25° (Melville thrust) and 20° (Mpambanyoni River thrust), both in the Margate terrane. Later transcurrent shear zones (Lilani-Matigulu) in the Tugela terrane show dips of more than 80°.

N Nguuri T, Gore J, James DE, Webb SJ, Wright C, Zengeni TG, Gwavava O, Snoke A, and Kaapvaal Seismic Group

Geophysical Research Letters, 28(13)

2501- 2504.

Crustal structure beneath southern Africa and its implications for the formation and evolution of the Kaapvaal and Zimbabwe cratons

Keywords: crust, mantle, Moho, thickness

2001 Early processes that were responsible for the formation of the Archaean crust were unique. Receiver functions from broadband stations show that the nature of the crust across southern Africa and the mantle-crust boundary between Archaean and post-Archaean have significant differences. The crust beneath the undisturbed Archaean crust/craton is typically thin (about 35-40 km), unlayered and characterised by a significant velocity contrast across the relatively sharp Moho. Toward the Bushveld Complex (north of the craton), the crust is thickened and reaches values of about 50 km. Here the authors report that the area of thickened crust correspond with reduced upper mantle velocities from body wave tomography. The Moho beneath the Archaean crust is relatively simple. In Archaean areas that have been modified by Proterozoic processes, where the crust is thicker, the Moho is complex. The Moho beneath the Kaapvaal craton yields sharp and large amplitude Ps signals.

Yes The change in thickness of the crust below the Kaapvaal craton varying from typically 50 km around the Limpopo belt, 40 km around the Bushveld Complex and 35 km south of the Bushveld complex.

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Fan G and Wallace T

Seismological Research Letter 66 (5)

13-18

Focal Mechanism of a recent event in South Africa: A study using a sparse very broadband network

Keywords: focal, mechanism, strike-slip, seismicity

1995 Using very broadband network, the 30 October 1994 event close to the northwestern border of the Free State Province with magnitude 5.7, is concluded to have normal-slip focal mechanism. This is consistent with other studies earthquakes in the region. The northeast-southwest trend of seismicity in the Kaapvaal craton may be related to the north-northeast structural trends observed in deep mines. Large event are not related to mine activity. Strike-slip focal mechanisms are observed for the Ceres earthquake in the western Cape. In this region, the travel times of the P- and S- waves indicate that there crust has more than 1 layer and has a total thickness of about 36km. Focal depth from moment tensor inversion ranges between 9 and 12 km. Focal mechanism of this earthquake are similar to those of the 1 July 1976 Koffiefontein event. This Koffiefontein event has two conflicting fault plane solutions; normal-slip faulting dominated by east-west tension stresses (from P-wave movements) and oblique-slip faulting with strike-slip component dominated by east-west principal compressive stresses. Since there is no surface faulting, it is difficult to resolve these solutions. The

Yes Events on the Kaapvaal craton have normal-slip focal mechanisms

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authors prefer a normal-slip model for the 1976 event. The 5 October 1986 event in the Cedarville zone (southeast of Lesotho) has normal-slip focal mechanism, similar to the already discussed events. The type of focal mechanism discussed here may be related to the east-west pattern of deformation in this part of South Africa. Seismicity may also be related to regional uplift.

Johnston ST, McCourt S, Bisnath A and Mitchell AA

SAJG 106

85-97

The Tugela terrane, Natal Belt: Kibaran magmatism and tectonism along the southeast margin of the Kaapvaal Craton

Keywords: terrane, tectonic, overthrust, Tugela

2003 The Tugela terrane is interpreted as an assemblage of discreet, oceanic arc related tectonic elements including minor ophiolite components. In the Tugela terrane resting on the Kibaran Natal belt, at least three episodes of deformation from the obliteration of primary structures by subsequent deformation to high grade metamorphism to fold, faults and shear zones are observed. The products of the three tectonic events here include the magmatic sequence (older than 1152 Ma) is attributable to rifting of the young crust in an arc setting, sheared and tectonically dismembered ophiolite sequence. The granulite facies metamorphism in this terrane is younger than 115 Ma. During top to the north shearing, the deeply buried assemblage was exhumed and gave rise to north verging folds and faults. All these events indicate basin closure, collision with and overthrusting of the belt on the Kaapvaal craton. The voluminous granitoids in this are possibly linked to subduction or melting during exhumation.

Yes In the Tugela terrane resting on the Kibaran Natal belt, at least three episodes of deformation from the obliteration of primary structures by subsequent deformation to high grade metamorphism to fold, faults and shear zones are observed.

RS

Matthews PE

Nature 240

37-39

Possible Precambrian obduction and plate tectonics in southern Africa

Keywords: terrane, nappes, imbricate, collision

1972 The Tugela terrane is composed of four stacks thrust nappes which are flat-lying. This terrane, which represents the low oceanic part of the ophiolite sequence, is interpreted as an imbricate thrust zone in which Proterozoic ophiolite rocks were obducted northward into the southern part of the Kaapvaal craton. The contact between the Natal metamorphic province and the Kaapvaal craton is marked by major thrust zones. These large scale inverted metamorphic sequences show that crustal scale thrusting has taken place and support the collision models.

Yes The contact between the Natal crust and the Kaapvaal Craton is an imbricate thrust zone by which the Tugela terrane was obducted during the Namaqua-Natal orogeny. The Tugela terrane in KwaZulu Natal situated south of the Kaapvaal Craton hosts ophiolites which were obducted on to the craton by a northeast directed thrusting as four major nappes. The border between the Kaapvaal craton and the Namaqua-Natal mobile belt, which is exposed in the Natal sector.

RS

Olivier HJ

Transactions of the Geological Society of South Africa

75

197-224

Geohydrological investigation of the flooding at Shaft 2, Orange-Fish tunnel, north-eastern Cape Province

Keywords: Doringberg, fault

1972 An arcuate belt of gravity highs extending from the Doringberg fault near Prieska to the post-Karoo faults in Lesotho suggest a possible existence of a major fault system which has been reactivated during post-dolerite times. The Doringberg fault south west of the craton is interpreted to be an area of crustal weakness along the Kaapvaal craton

Yes The Doringberg fault is interpreted to be an area of crustal weakness along the Kaapvaal craton

RS

Karoo Seismic Source Zone

Johnson, MR, Van Vuuren, CJ, Visser, JNJ, Cole, DI

Sedimentary rocks of the Karoo Supergroup

2006 The Karoo Supergroup ranges in age from the Late Carboniferous to Middle Jurassic and has a cumulative thickness of about 12 km. The Main Karoo basin overlies the stable Kaapvaal craton in the

Yes The Karoo Supergroup ranges in age from the Late Carboniferous to Middle Jurassic.

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Wickens, H. de V, Christie, AMD, Roberts, DL and Brandl, G

The geology of South Africa (Johnson, Anhaeusser, and Thomas: eds.)

461- 500

Keywords: Karoo, foreland, retro-arc, Kaapvaal, belt, mobile

north and the Namaqua-Natal mobile belt in the south and bounded along the margin of the Cape Fold Belt. The Karoo consists of a retro-arc foreland basin.

Watkeys, MK

The geology of South Africa

Johnson, Anhaeusser, and Thomas: eds.)

531- 540

Gondwana break-up: a South African perspective

Keywords: fracture, zone, break-up, Karoo, volcanism

2006 Gondwanaland (Africa, S America, India, Antarctica, Madagascar, Australia and others) is a product of the split of Pangaea during the Triassic. The break-up of Gondwanaland is the most important geological event that occurred in the southern hemisphere and is responsible to how continent are shaped today. Most evidence of the breakup of Gondwanaland is preserved in the offshore basins on the continental shelf of southern Africa, but less onshore as the Karoo volcanism. The dextral Agulhas Falkland Fracture Zone (AFFZ) resulted from the rifting of Gondwanaland and may have been responsible for incipient rifting propagating into the South Atlantic in the Late Jurassic and early Cretaceous. The AFFZ is an intracontinental 1200 km long transform fault and offset spreading ridges in the South Atlantic and Natal Valley.

Yes The dextral AFFZ resulted from the rifting of Gondwanaland.

RS

Thomas RJ, von Veh MW and McCourt S

Full paper

Journal of African Earth Science

16 (1/2), 2-24

The tectonic evolution of southern Africa: an overview

Keywords: Gondwana rifting, Kaapvaal stability, tectonic framework, crustal growth

1993 This is the summary of this paper: 1. The Kaapvaal Craton showed stability around 3.0 Ga. 2. The Beattie Anomaly in the Cape Province is evidence of the

position of the subduction zone where the Saldania Province was probably pulled beneath the older continental crust. This anomaly could possibly also point to some kind of Pan-African suture zone (However, Lindeque and others studied a seismic profile that cut that anomaly and saw no evidence of an ancient suture).

3. The direction of deformation in the Saldania Province was toward the northeast. Although the Cape Orogeny (Permo-Triassic) may have left a print, there is evidence of about two deformation phases in the Saldania province. Early north- to northeast-verging folding was followed by major thrusting in the north direction which was associated with syn-tectonic granite intrusion. The direction of tectonic transport was progressively being pointed toward the east.

4. During the Cape Orogeny, a retro-arc had foreland basin formed and was now migrating to the northeast. Is this in preparation for the deposition of the Karoo Supergroup?

5. The orogenic transport in the Cape was pointing toward the north. (This orogenic belt can be traced in Australia, Antarctica and South America).

6. The Cape Fold Belt slightly convex southern branch (separated from the western branch by a syntaxis) is dominated by north-verging tight folds, thrust and detachment faults. These become open folds toward the northern direction.

7. Four deformation pulses (supported by Halbich et al. 1983)

Yes The Natal sector accommodates 3 discontinuous tectonostratigraphic domains; the Tugela, Mzumbe and Margate terranes which are part of a juvenile orogen. The craton stabilised at about 3.0 – 2.6 Ga. reported Mesoproterozoic intrusions which tectonically affected the Mzumbe and Margate terranes. Both dextral and sinistral strike-slip faulting is present in the NAM zone. Some of the structures such as the Brakbos shear zone were initially left-lateral and were later reactivated as dextral transcurrent shear zones.

GIS_D1024_F3_Thomas_et_al_1993.tif

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which occurred along the same axis were recognised. 8. The western branch of the Cape Fold Belt is thought to have

formed before the southern branch. This is supposed to have happened by vertical tectonics. However, other workers argue for coeval formation of the two deformation branches.

9. The break-up of Gondwana can be divided into two phases a. Break-up (separation) of east and west Gondwana resulted in

inversion of thrust faults. b. Rifting associated with the separation of Africa and South

America at 135 Ma resulted in the development of the Agulhas-Falkland fracture zone (east of South Africa). This rifting also caused the rotation of the Falk Islands. The direction of the rotation was clockwise. This second phase was ended by a regional rift-drift unconformity offshore. However, compressional and extensional fault movement continued into the Tertiary times.

10. Extensional and right lateral transtensional tectonics occurred in the east of the SA coast.

11. Tectonic processes have been active from Mid-Archaean to recent times.

De Beer JH, Van Zijl JSV and Gough DI

Tectonophysics, 83(3/4), 205-225

The southern cape conductive belt (South Africa): its composition, origin and tectonic significance

Keywords: anomaly, palaeosuture, subduction, Gondwanaland

1982 The Southern Cape conductive belt (SSCB) was discovered by magnetometer array studies. The geophysical anomaly lies across southern part of South Africa; running from the west to the east coast. The SSCB corresponds with the zone of weakness which has been exploited by three major geosynclinal accumulations over a period of 600 Myrs. The Beattie magnetic anomaly, which stands out from the magnetically neutral Karoo crust, is the largest terrestrial and electrically conductive anomaly in the world and spans almost 1000 km in length. The Beattie magnetic anomaly is represents a Neoproterozoic palaeosuture represented by a steeply dipping ophiollite. The SCCB is a result of the accumulation of marine sediments and oceanic lithosphere at the top of the Proterozoic subduction whish ceased in the period between 1.0 and 0.8 Ga. Around and adjacent the area of the SCCB, there may be evidence of three subduction zones. The third subduction zone may be off the Permian Gondwanaland. The SCCB is associated with and correlates with the Beattie magnetic anomaly.

Yes The 1000 km long Beattie magnetic anomaly; the largest terrestrial and electrically conductive anomaly in the world stands out from the magnetically neutral Karoo crust. The origin of the Beattie magnetic anomaly is regarded as a Neoproterozoic palaeosuture represented by a steeply dipping ophiollite. The SCCB is a result of accumulation of marine sediments and oceanic lithosphere associated with a Proterozoic subduction.

RS

Thomas RJ, Marshall CGA and Du Plessis A

Inversion Tectonics of the Cape Fold Belt, Karoo and Cretaceous Basins (De Wit and Ransome, eds)

229-236

Geological studies in southern Natal and Transkei: implications for the Cape Orogen

Keywords: anomaly, Natal-crust, neutral

1992 The Beattie anomaly is referred to here as a large east-west trending static-field magnetic anomaly. The authors here talk about Beattie set anomalies causing the Natal-type crust to be ‘striped’. These positive anomalies are separated by belts of crust of similar dimensions with low magnetic susceptibility. Of these, the Beattie anomaly is the most prominent. In the south, the Beattie and Mbashe magnetic anomalies are truncated by east-west trending zone of magnetically neutral crust. In the west, the Beattie and Williston magnetic anomalies are cut neutrally magnetic Pan African crust. This boundary also marks the approximate position of the eastern limit of folding in the western branch of the Cape Fold Belt.

Yes The Williston magnetic anomaly which separates the magnetically neutral crust of the Saldanian belt from the Namaqua crust which is typified by small but randomly oriented anomalies. The western boundary is also where the Williston and Beattie magnetic anomalies are truncated by the magnetically neutral crust which may be Pan-African in age and where the Saldanian province is positioned. The Natal crust is


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considered as the magnetically ‘striped’ belt.

Du Plessis A and Thomas RJ

2nd

Annual Technical Meeting of the South African Geophysical Association, Pretoria

57-59

Conference abstract

Discussion on the causative bodies of the Beattie-set of magnetic anomalies

Keywords: oceanic crust, causative, allochthons

1991 The Beattie-set consists of five major anomalies that trend in the east-southeast–-west-northwest direction. These are traced from on land to the coast in the southeastern part of South Africa. Starting from the Tugela region to toward the south, the anomalies are the Empangeni, Durban, Amanzimtoti, Beattie and the Mbashe anomalies. Because the Beattie and Mbashe anomalies terminate in the west (Cape Province), these authors believe that this indicates the border of the oceanic crust against the continent. The causative body of the Beattie anomaly may be between 5 (most probably) and 10 km on depth. Of the five anomalies, three which are in the CK zone are associated with the Mzumbe amphibolite facies. (The remaining two are in the Karoo zone – the Beattie and Mbashe). In addition to them having similar orientations, the Beattie-set anomalies may be related to one another because the causative bodies have similar shapes. It is possible that the causative bodies include Kibaran-age wedge-shaped slivers of magnetic material bounded mainly by shallow S-dipping faults and may be preserved allochthons of pre-existing extensive layer.

Yes Because of its proximity, direction of strike and sub-parallel nature to the main Beattie anomaly, the Mbashe positive magnetic anomaly is one of the Beattie-set magnetic anomalies.

RS

Weckmann U, Ritter O, Jung A, Branch T and De Wit M.

Journal of Geophysical Research 112

1-10

Magnetotelluric measurement across the Beattie magnetic anomaly and the Southern Cape conductive Belt, South Africa

Keywords: continental, depth, Gondwana, midcrust, oceanic

2007 The Beattie magnetic anomaly (BMA) and the Southern Cape Conductive Belt (SCCB) are two of the largest terrestrial geophysical anomalies in the world that extend across the southern African continent; cover almost the entire (1000 km) east-west extent of South Africa, truncated by the Agulhas Fracture Zone in the east and the margin of the south Atlantic in the west following the break-up of Gondwanaland. A high conductivity anomaly is resolved 5-10 km below the trace surface of the east-west BMA. A regionally continuous 50-70 m thick subhorizontal band of pyritic carbonaceous (shale?) is intersected at shallow depths. The high conductivity band in this study coincides with this pyritic Whitehill Formation shale at depths between 2 and 5 km (from borehole intersections). Several high conductivity features in the midcrust. In some models (e.g. Pitts et al., 1992), the BMA is about 30 km thick and dips to the S from 7 km below the surface reaching a depth of about 30 km. The southern boundary of the 140 km wide SCCB is about 40 km below the Cape Fold Belt and the northern boundary is almost along the Great Escarpment. The SCCB may be at a depth of the lower crustal or upper mantle. The BMA and the northern boundary of the SCCB are coincident. This is why a single source is generally assumed. However, it is assumed here that the origin of these anomalies is not necessarily the same. The conductors below the surface trace of the BMA are located in the midcrust and are likely to be Mesoproterozoic structures (mineralised tectonic synforms??) within the Namaqua-Natal metamorphic belt (NNMB) as opposed to the serpentinised oceanic crust in a crystallise basement as assumed by other workers (e.g. de Beer et al, 1982).

Yes The Southern Cape Conductive Belt (SCCB), which nearly coincides with the Beattie magnetic anomaly and is also the largest geophysical anomaly in the world. The Beattie magnetic anomaly, which stands out from the magnetically neutral Karoo crust, is the largest terrestrial and electrically conductive anomaly in the world and spans almost 1000km in length. Suggesting that the conductors below the axis of the Beattie magnetic anomaly may be Mesoproterozoic structures.

GIS_X1002_F1_Weckmann_et_al_2007.tif

RS

Weckmann U, Branch Comparing magnetic and magnetotelluric data for the Beattie

2005 Both the BMA and the SCCB are within the NNMB and the CFB. This may mean that there is tectonic interpretation. A conductor

Yes The SCCB and the Beattie magnetic anomaly may not

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T and Ritter O

Kolliquium Elektromagnetische Tiefenforschung, Haus Wohldenberg, Holle, 3-7 October

302-306

Conference abstract

Magnetic Anomaly, South Africa

Keywords: tectonic, boundary, enrichment, graphite

(Whitehill Formation shale) is located 5-10 km below the trace of the BMA and another one located from shallow crust to a depth of 20 km below the southern boundary of the SCCB. These conductors may be faults which have undergone graphite enrichment along shear planes. The authors argue that such a plane could cut through the magnetic body without changing the magnetic response significantly. The BMA and the SCCB are not of the same source.

necessarily have the same source or origin.

Pitts BE, Maher MJ

and De Beer JH

Inversion Tectonics of

the Cape Fold Belt,

Karoo and

Cretaceous Basins

(De Wit and

Ransome, eds)

27-32

Interpretation of magnetic, gravity and magnetotelluric data across the Cape Fold Belt and Karoo Basin

Keywords: crust, gravity, anomaly, isostatic

1992 The Southern Cape Conductive belt (SCCB), Beattie magnetic anomaly and the Southern Cape Isostatic (SCI) anomaly are hosted in the crust of the southern Cape Province. The SCCB and the Beattie magnetic anomaly are related to each other. The positive static Beattie magnetic anomaly may have formed before the break-up of Gondwanaland. The negative SCI anomaly has been associated with the non-compensatory east-west thickening of the crust south of the escarpment. This negative gravity anomaly may have been related to deficiency of isostatic compensation following the erosion of material south of the escarpment because of natural strength of the crust around that area. The Beattie magnetic anomaly is caused by a 30 km wide and 7 km deep body dipping toward the south below the surface

Yes The negative Southern Cape isostatic anomaly is situated north of the eastern end of the Kango fault. This negative gravity anomaly may have been related to deficiency of isostatic compensation following the erosion of material south of the escarpment because of natural strength of the crust around that area.

RS

Quesnel, Y,

Weckmann, U, Ritter,

O, Stankiewicz, J,

Lesur, V, Mandea, M,

Langlais, B, Sotin, C,

and Galdéano, A

Tectonophysics, 478,

111- 118.

Simple models for the Beattie Magnetic Anomaly in South Africa

Keywords: magnetotelluric, midcrust, palaeo-, oceanic, crust, conductivity, magnetised

2009 The origin of the BMA is still a contentious issue. The source of the BMA is mostly located in the midcrust and may be displaced by a shear zone or fault. In contrast to other models, the authors here suggested that their best-fitting model corresponds to 2 wide and highly magnetised sheet-like prisms which may be related to granulite-facies rocks with exsolved hematite-ilmenite in midcrust within the NNMB. High resolution magnetotelluric measurements across the SCCB suggest that the SCCB is an integration of a series of localised zones of high conductivity within the NNMB and not a deep and broad homogenous zone of high conductivity (see Weckmann et al., 2007). In contrast to some of their published papers, these authors see to now agree with the serpentinised palaeo-oceanic crust that reached depths of about 30 km (by de Beer et al., 1982; Pitts et al., 1992). This is because of similar high magnetisation intensity values obtained from serpentinised oceanic crust in the Alps. Such rocks also show seismic velocities comparable to those estimated for the high-velocity zone below the BMA (about 7 km/s). They could also be associated with zones of high electrical conductivity but only in active regimes with fluids. Modern electrical conductivity for serpentinite without fluids is poor. The serpentinite would become conductive if it contained interconnected magnetite over large areas be means of shearing.

Yes The Beattie magnetic anomaly, which stands out from the magnetically neutral Karoo crust, is the largest terrestrial and electrically conductive anomaly in the world and spans almost 1000km in length. The source of the Beattie anomaly may be a two wide and highly magnetised sheet-like prisms situated at depths of 10 to 20 km in the mid-crust.

RS

Lindeque AS and De Wit MJ

11th South African

Geophysical

Revealing the Beattie Magnetic Anomaly and the anatomy of the crust southernmost Africa: Geophysics and deep subsurface

2009 The deep crust of the south part of South Africa contains unresolved tectonic features some of which are the BMA, CFB and the Karoo basin. Using surface geology and several geophysical methods, four components of thrusts are differentiated according to

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Association Biennial Technical meeting and exhibition, Swaziland,

490-499

geology where the Cape Fold Belt and the Karoo meet

Keywords: massive, disseminated, Namaqua-Natal, mobile, crust, aeromagnetic, reflectivity

thickness of the crust in the Mesoproterozoic Namaqua-Natal crust. The BMA is interpreted to be a Namaqua-like massive to disseminated, deformed/metamorphosed stratiform sulphide ore body. The NNMB is about 13-21 km thick and has a distinct north-dipping seismic fabric and contains the BMA. According to data provided here, it is suggested that he NNMB continues below the CFB and may well extend even toward the south continental margin. The position of the BMA depicted from aeromagnetic data corresponds to two complex zones of higher reflectivity in the midcrust.

Lindeque AS, De Wit MJ, Ryberg T, Weber M and Chevallier L

SAJG 114 (3-4)

265-292

Deep crustal profile across the southern Karoo basin and Beattie magnetic anomaly, South Africa: An integrated interpretation with tectonic implications

Keywords: tectonic, thrust, fracture zone, collision, Namaqua-Natal, subduction

2011 The model here shows a complex tectonic crust of the southern part of South Africa. The Cape Supergroup rests unconformably on the flat and shallow dipping NNMB for about a 100 km to the south and possibly even further and perhaps even to the Agulhas Falkland fracture zone. The depth of the fore-deep basin of the southern Karoo is not as significant as reported and the shortening of the tectonic front through a series of low-angle listric thrusts and fold detached from NNMB basement and the Karoo Supergroup. The data here also support a collisional tectonic setting and far-field subduction to the south with the Karoo basin developing ahead of the thin-skinned Jura-type fold belt as opposed to a retro-arc foreland generally modelled. This is supported by the absence of a thick crustal root below the CFB front. The NNMB if related to the formation of accretionary arc at a subduction zone dipping to the south. This is followed by a continental collision outward the modern continental margin of South Africa. Two complex regions of reflectivity in the midcrust (7-15 km) correspond to the position of the BMA (maximum axes in aeromagnetic data). These two regions lie within the NNMB high grade rocks in the midcrust and these may be the source of the BMA. This is contrast to the previous model of the source of the BMA being a Pan-Africa palaeo-suture. The high conductivity anomalies in the magnetotelluric data correspond in space to the two zones of higher reflectivity seen in the seismic data but appear to transect seismic reflectors. The source of the BMA may be related to a conductive ore body or a collective of bodies stacked through thrusting and subsequent metasomatic modification.

Yes The Beattie anomaly in the mid-crust is present at depths between 7 and 15 km with a thickness of about 6km may be a result of a Namaqua-like stratabound and massive sulphide ore body.

RS

Stankiewicz, J, Parsiegla, N, Ryberg, T, Gohl, K, Weckmann, U, Trumbull, R and Weber, M

Journal of Geophysical Research

113, B10313, doi: 10.1029/2008JB005612.

Crustal structure of the southern margin of the African continent: results from geophysical experiments

Keywords: geophysical, fracture, zone, oceanic, continental, crust, Moho, seismic , margin

2008 With onshore and offshore geophysical experiments, it is observed

that the Moho depth decreases rapidly from about 40 km inland to

30 km toward the coast of South Africa before gently thinning

toward the Agulhas Fracture zone which marks the transition zone

between the continental and oceanic crust. This change is close to

the boundary between the CFB and the NNMB. The crust toward

the coast is about 7 km with seismic velocities more than 7 km/s.

The Moho depth decreases sharply where the crust has been

extended. The extended crust shows a gradual thinning on the

sheared Agulhas margin. This is where seismic velocities are low.

Yes The change in depth of the Moho from 40 km to 30 km is support to the position of the Mesozoic extension in South Africa.

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Yeari


Is the data used

in the SSC

model? (yes, no)


5 Originator

This is in contrast to the higher seismic velocities observed in the

crust above the keel.

At the centre of the BMA, a zone of anomalously high velocity

(7km/s) at a depth of about 15 km. a zone of high electrical

resistivity is also found in the same place. This zone is bound by

large midcrustal regions of stacked layers of high electrical

conductivity.

Stankiewicz, J, Ryberg, T, Schulze, A, Lindeque, A, Weber, M, and de Wit, M

SAJG, 110,

407- 418.

Initial results from wide-angle seismic refraction lines in the Southern Cape

Keywords: seismic, thrust, fault, tectonic, unconformity

2007 Two wide-angle on-shore seismic lines (along a 800 km transect)

collected roughly parallel to each other approximately 200 km apart,

starting at Mossel Bay and St. Francis, and running about 200 km

north to Fraserburg and Graaf Reinet, respectively. The profiles

cross a wide variety of geological terrains, such as the siliciclastic

sequences of the Palaeozoic – Mesozoic Karoo and Oudtshoorn

basins, the lower Palaeozoic Cape Fold Belt, and the Neocambrian

Kango and Kaaimans inliers including the BMA. There is good

correlation of the shallow features with surface rock type. Deeper

down both the stratigraphic and tectonic contacts between

geological groups can be identified. These include an inferred

possible blind Palaeozoic thrust fault, and the unconformity

between the Cape Supergroup and the Namaqua-Natal

Metamorphic Complex. The normal listric geometry of the Kango

and Gamtoos Faults is clearly seen to a minimum depth of 15 km.

High velocity anomaly within the NNMC at ~10 km depth that can

be related to the source of the Beattie Magnetic Anomaly Is also

observed.

No RS



95

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101

Table 3.4. Data Summary Table - Entire SCC Model, Global Assessments, Thyspunt PSHA.

Author Title Year Description and Relevance to SSC

Is The Data Used in the

SSC Model?

(Yes, No) Discussion of Potential Data

Use GIS Code Originator

Anderson, J.G. Estimating Seismicity from

Geological Structures for

Seismic Risk Studies

1979 This paper provides a methodology for translating fault slip

rate into seismic moment rate by incorporating the

seismogenic fault area and assuming that all of the fault slip

becomes seismic moment. The formulation assumes an

exponential magnitude-frequency model and it is suggested

that the b-value come from the regional seismicity and the

Mmax comes from fault-specific information.

Yes The conceptual model of using fault slip rate for seismic moment rate is used for the fault sources

KC

Clark et al. Australia’s seismogenic

neotectonic record: A case for

heterogeneous intraplate

deformation

2011 This paper is devoted to summarizing all available

neotectonic data regarding faults in Australia, and then

providing a discussion of possible domains within which the

behavior of faults is assessed to be relatively consistent.

The important data for the SSC model includes a

compilation of evidence of temporal clustering for SCR

faults. This includes SCR data regarding the number of

events that occur within temporal cluster and ratio of the

within-cluster intervals to the out-of-cluster intervals.

Yes Analogue data can be used to interpret the recurrence history of the Kango fault and to make an assessment of temporal clustering.

KC

Collettini & Sibson Normal faults: normal friction? 2001 This paper addresses the debate regarding whether normal

faults may be seismically active at very low dips in the

upper continental crust. An updated compilation of dip

estimates (n = 25) has been prepared from focal

mechanisms of shallow, intracontinental, normal-slip

earthquakes where the rupture plane is unambiguously

discriminated. The dip distribution for these moderate-to-

large normal fault ruptures extends from 25° < d < 60°. This

compilation of the dip of coseismic normal faults as

determined by reliable focal mechanisms and aftershocks is

useful for assessing the dip of future normal-faulting

earthquakes.

Yes Used to develop generic fault dip distribution for virtual faults in source zones that are assessed to be normal faults, or fault sources whose downdip geometry is not well-constrained.

KC

Gutenberg & Richter Earthquake magnitude,

intensity, energy and

acceleration

1956 One of the first compilations of global earthquakes and

estimates of the magnitudes for those events. Numbers of

earthquakes of various magnitudes are plotted and the

conclusion is made that magnitudes are exponentially

distributed.

Yes Provides the basic exponential form to the magnitude-frequency relationship for source zones.

KC

Hanks & Kanamori A moment magnitude scale. 1979 Develops the empirical and theoretical basis for defining a

moment magnitude that is directly related to seismic

Yes Can be used to translate fault slip rate and rupture geometry into a seismic moment rate

KC


102



SSC Model?



moment, assuming basic information regarding the strength

characteristics of the fault zone. The paper provides the

basic relationship that can be used to translate seismic

moment to moment magnitude. Using this relationship,

seismic moment rate can be directly translated into a fault-

specific recurrence rate using an applicable magnitude-

frequency model.

Jackson & White Normal faulting in the upper

continental crust: observations

from regions of active extension

1989 Provides a compilation of a number of coseismic normal

faulting earthquakes with the goal of dealing with the issue

of whether the low-angle faults mapped in many areas are

seismogenic. It is concluded that the shallowest dips of

seismogenic normal faults are about 30 degrees, and no

dips for seismogenic normal faults are shallower than 20

degrees.

Yes Used to assist in the development of generic fault dip distribution for virtual faults in source zones that are assessed to be normal faults, or fault sources whose downdip geometry is not well-constrained

KC

Johnston et al. The Earthquakes of Stable

Continental Regions.

1994 Major study sponsored by EPRI with the aim of establishing

a strong technical basis for Mmax assessments. The term

and concept of stable continental regions (SCR) is defined

by specific criteria relating to the timing and nature of major

tectonic activity and structures associated with that activity.

Given this definition, SCRs are defined worldwide and each

is characterized according to the timing of tectonism and

the geologic structures that exist. As part of the study,

catalogue was constructed of earthquakes having M>4.5

for global SCRs. To arrive at a consistent moment

magnitude estimate for each earthquake, a number of

earthquake magnitude conversion relationships were

developed for a number of earthquake size measures,

particularly intensity measures. Based on the tectonic

characterization and the SCR earthquake catalogue, a

Bayesian procedure is developed for assessing Mmax. The

prior distributions are developed based on the general

characteristics of various tectonic domains. These prior

distributions were subsequently updated as part of the

CEUS SSC project (USNRC 2012).

Yes Provides definition of stable continental regions (SCR) based on geologic and tectonic criteria, Bayesian approach to assessing Mmax, and recurrence approach to calculate maximum likelihood estimates of the α(m0) and β parameters that are conditional on Mmax, for seismic source zones

KC

Kafka Does seismicity delineate zones

where future large earthquakes

are likely to occur in intraplate

environments?

2007 The spatial distribution of seismicity is often used as one of

the indicators of zones where future large earthquakes are

likely to occur. This is particularly true for intraplate regions

such as the central and eastern United States, where

geology is markedly enigmatic for delineating seismically

No Although the quantitative data and “cellular seismology” approach is not used, the conceptual model of spatial stationarity provides support to the use of the spatial distribution of seismicity (i.e., differences in

KC


103



SSC Model?



active areas. This paper attempts to cast this problem in the

form of scientifically testable hypotheses and to test those

hypotheses. Three decades of global data from the

National Earthquake Information Center are used to explore

how the tendency for past seismicity to delineate locations

of future large earthquakes varies for regions with different

tectonic environments. Applying the results of this exercise

to the central and eastern United States, it is estimated that

future earthquakes in the central and eastern United States

(including large and damaging earthquakes) have ~86%

probability of occurring within 36 km of past earthquakes,

and ~60% probability of occurring within 14 km of past

earthquakes.

recurrence) as one criterion in defining seismic source zones

Kafka Use of Seismicity to Define

Seismic Sources: Application to

Eastern North America:

presentation given at CEUS

SSC Project Workshop #2

2009 Same concept as Kafka 2007 paper with updated data. No (see above) KC


104



SSC Model?



Kijko Estimation of the maximum

earthquake magnitude, mmax.

2004 This paper provides a generic equation for the evaluation of

the maximum earthquake magnitude Mmax for a given

seismogenic zone or entire region. The equation is capable

of generating solutions in different forms, depending on the

assumptions of the statistical distribution model and/or the

available information regarding past seismicity. It includes

the cases (i) when earthquake magnitudes are distributed

according to the doubly-truncated Gutenberg-Richter

relation, (ii) when the empirical magnitude distribution

deviates moderately from the Gutenberg-Richter relation,

and (iii) when no specific type of magnitude distribution is

assumed. Both synthetic, Monte-Carlo simulated seismic

event catalogues, and actual data from Southern California,

are used to demonstrate the procedures given for the

evaluation of Mmax.

The approach requires significant numbers of earthquakes

to have sufficient stability for application at the source zone

level.

Yes Has potential application for any source zone because it uses only the earthquake catalogue. However, the requirement for large numbers of earthquakes leads to instability in regions with low seismicity, such as the source zones in the Thyspunt PSHA.

KC

Kijko On Bayesian procedure for

maximum earthquake

magnitude estimation

2012 This work is focused on the Bayesian procedure for the

estimation of the regional maximum possible earthquake

magnitude Mmax. The paper briefly discusses the currently

used Bayesian procedure for Mmax, as developed by

Johnston et al., 1994, and a “statistically justifiable”

alternative approach is suggested. According to Kijko, the

fundamental problem in the application of the current

Bayesian formalism for Mmax estimation is that one of the

components of the posterior distribution is the sample

likelihood function, for which the range of observations

(earthquake magnitudes) depends on the unknown

parameter Mmax. This dependence is said to violate the

property of regularity of the maximum likelihood function.

The resulting likelihood function, therefore, reaches its

maximum at the maximum observed earthquake magnitude

and not at the required maximum possible magnitude

Mmax. Since the sample likelihood function is a key

component of the posterior distribution, the posterior

estimate of �ˆ max, is said to be biased. The degree of the

bias and its sign depend on the applied Bayesian estimator,

the quantity of information provided by the prior distribution,

and the sample likelihood function. It has been shown that if

the maximum posterior estimate is used, the bias is

No The paper assumes that the Bayesian approach uses the mode of the posterior distribution as the estimate of Mmax for purposes of PSHA, which is a criticism that was refuted in CEUS SSC report (USNRC 2012a). Also, the statement is made without support that mean Mmax is biased to large values: simulations done in CEUS SSC project (USNRC 2012a) show that mean Mmax is not biased.

KC


105



SSC Model?



negative and the resulting underestimation of Mmax can

be as big as 0.5 units of magnitude.

Kijko et al. Probabilistic PGA and spectral

acceleration seismic hazard

maps for South Africa [abstract]

2009 Brief statement of the same criticism of the Bayesian

approach to Mmax as given in Kijko 2012.

No KC


106



SSC Model?



Klose & Seeber Shallow seismicity in stable

continental regions

2007 A worldwide compilation of well-constrained fault ruptures

and focal depths of earthquakes reveals that the Earth’s

crust in many stable continental regions (SCRs) is

characterized by a bimodal depth distribution with a very

shallow upper crustal component. The distributions can

vary in a) depth of the modes and b) strength of bimodality,

probably due to intracrustal boundaries, differences in

frictional and rheological properties, heat-flow densities,

strain-rates, and tectonic forces or forces stemming from

the surface. Overall, SCR ruptures and SCR earthquakes

are confined within the upper third (0–10 km) and/or the

lower third of the crust (20–35 km), while the midcrust (10–

20 km) tends to be aseismic. Historical data indicate that

some SCRs show very well-developed bimodal distributions

of focal depths (e.g., North Alpine foreland basin in Europe,

Kachchh basin in India), while others show weak to no

developed bimodal distributions (e.g., Charlevoix seismic

zone, New Madrid seismic zone in the central United

States).

Yes Provides a basis for developing a depth distribution for the Thyspunt region and for testing whether or not the region shows evidence of depths below 20km, thus defining a bi-model distribution, or simply shows a unimodal distribution

KC

Leonard Earthquake fault scaling: Self-

consistent relating of rupture

length, width, average

displacement, and moment

release.

2010 This paper develops a series of self-consistent equations

that describe the scaling between seismic moment, rupture

area, length, width, and average displacement. In addition

to β, the equations have only two variables, C1 and C2,

which have been estimated empirically for different tectonic

settings. The relations predict linear log–log relationships,

the slope of which depends only on β.

These new scaling relations are self-consistent, in that they

enable moment, rupture length, width, area, and

displacement to be estimated from each other and with

these estimates all being consistent with the definition of

seismic moment. I interpret C1 as depending on the size at

which a rupture transitions from having a constant aspect

ratio to following a power law and C2 as depending on the

displacement per unit area of fault rupture and so static

stress drop. It is likely that these variables differ between

tectonic environments; this might explain much of the

scatter in the empirical data.

Yes Defines a relationship between moment magnitude and rupture length for SCRs, which can be used to estimate characteristic magnitudes for fault sources and in the hazard analysis to define the lengths of ruptures on virtual faults. Scatter in the SCR relationship is very small and likely due to the small number of data points.

KC

NAGRA Probabilistic Seismic Hazard

Analysis for Swiss Nuclear

2004 Also called the PEGASOS study, this was a major SSHAC

Level 4 PSHA conducted for the four NPP sites in

Switzerland. The SSC model included the use of the

Yes The approach to magnitude-weighting of the depth distribution is useful for the SSC model, but the assessment of

KC


107



SSC Model?



Power Plant Sites Bayesian Mmax approach developed by Johnston et al.

(1994) and the Kijko approach (2004). A number of

innovations were developed for the SSC model including

various types of spatial smoothing of recurrence

parameters, various magnitude conversions to arrive at a

uniform moment magnitude, and incorporation of the

uncertainty in the magnitude estimates into the recurrence

calculations. One methodology that was developed as part

of the PEGASOS study is an approach to assessing the

depth distribution of future moderate-to-large earthquakes.

Beginning with the focal depth distribution from small

earthquakes, a magnitude-weighting function is developed

that accounts for the observation that larger magnitudes

tend to nucleate deeper in the seismogenic crust.

the lower fraction T must be made by the TI Team.

Petersen et al. Documentation for the 2008

Update of the United States

National Seismic Hazard Maps

2008 This document provides the technical discussion of the

bases for the elements of the US National Seismic Hazard

Map. Several methodological elements are similar to those

used in the Thyspunt PSHA, such as the characterization of

seismic sources using logic trees and assessing Mmax

based on analogues to SCRs. The seismic source model

includes both fault sources and seismic source zones. For

fault sources, a characteristic earthquake magnitude-

frequency model (Youngs & Coppersmith 1985) is used for

earthquake recurrence assessment.

Yes The adoption of the characteristic earthquake model can be used to substantiate the potential use of the model for the Thyspunt PSHA

KC

Scholz Earthquakes and friction laws

1998 This paper presents a complete constitutive law for rock

friction that was developed based on laboratory studies.

The law for rock friction now shows is used to explain

several earthquake phenomena—seismogenesis and

seismic coupling, pre- and post-seismic phenomena, and

the insensitivity of earthquakes to stress transients.

Importantly, the focal depth distribution of earthquakes is

used as an indicator of conditions in the crust that

considered to be unstable, conditionally stable, and stable.

This observation provides a conceptual basis for using the

depth distribution of earthquakes to characterize the state

of rock friction for future moderate-to-large earthquakes.

No Provides a conceptual basis for the use of focal depth distributions for assessing seismogenic thickness.

KC

Schwartz & Fault behavior and 1984 Paleoseismological data for the Wasatch and San Andreas No Provides the conceptual basis


108



SSC Model?



Coppersmith characteristic earthquakes:

examples from the Wasatch

and San Andreas fault zones

fault zones have led to the formulation of the characteristic earthquake model, which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes n ear the maximum. Analysis of scarp-derived colluvium in trench exposures across the Wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes. Comparisons of earthquake recurrence relationships on both the Wasatch and San Andreas faults based on historical seismicity data and geologic data show that a linear (constant b-value) extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes. Only by assuming a low b-value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes.

for the characteristic earthquake model, whose formulation is given in Youngs & Coppersmith (1985)

Schulte & Mooney An updated global earthquake

catalogue for stable continental

regions: Reassessing the

correlation with ancient rifts

2005 This paper presents an updated global earthquake catalogue for stable continental regions. The database contains information on location, magnitude, seismic moment and focal mechanisms for over 1300 M (moment magnitude) ≥ 4.5 historic and instrumentally recorded crustal events. Using this updated earthquake database in combination with a recently published global catalogue of rifts, the correlation of intraplate seismicity with ancient rifts is assessed on a global scale. Each tectonic event is put into one of five categories based on location: (i) interior rifts/taphrogens, (ii) rifted continental margins, (iii) non-rifted crust, (iv) possible interior rifts and (v) possible rifted margins. We find that approximately 27 per cent of all events are classified as interior rifts (i), 25 per cent are rifted continental margins (ii), 36 per cent are within non-rifted crust (iii) and 12 per cent (iv and v) remain uncertain. Thus, over half (52 per cent) of all events are associated with rifted crust, although within the continental interiors (i.e. away from continental margins), non-rifted crust has experienced more earthquakes than interior rifts. No major change in distribution is found if only large (M≥ 6.0) earthquakes are considered. The largest events (M≥ 7.0) however, have occurred predominantly within rifts (50 per cent) and continental margins (43 per cent).

No Database is an update from the Johnston et al. (1994) study, but the conclusions are essentially the same. This catalogue was used in the CEUS SSC study (USNRC 2012a) to update the prior distributions for Mmax.

KC

Stirling et al. Comparison of Earthquake Scaling Relations Derived from Data of the Instrumental and Preinstrumental Era

2002 Estimates of surface rupture displacement and magnitude for crustal earthquakes from the preinstrumental era (pre-1900) tend to be greater than the corresponding estimates derived from modern scaling relations. This tendency is investigated using an expanded and updated version of the earthquake dataset of Wells and Coppersmith (1994) to fit

No The comparisons of existing relations shows that there is good agreement in the moderate-to-large magnitude range, with discrepancies in the smaller magnitudes. However,

KC


109



SSC Model?



regression relations of moment magnitude on surface rupture length and rupture area and average surface displacement on surface rupture length. Separate relations are fitted to preinstrumental and instrumental data and the results compared to the equivalent relations of Wells and Coppersmith. We find that our relations for instrumental data remove some, but not all, of the differences between the preinstrumental data and the relations of Wells and Coppersmith. The remaining differences are attributed largely to natural censoring of surface displacements less than about 1 m and surface rupture lengths less than about 5 km from the dataset for the preinstrumental era because regressions constructed from similarly censored instrumental data are indistinguishable from the preinstrumental regressions. Since the regressions for our censored instrumental data (i.e., restricted to moderate to large earthquakes) are different from regressions for our complete dataset of instrumental earthquakes and from the regressions of Wells and Coppersmith (both with a larger proportion of small-to-moderate earthquakes), the results may indicate that large earthquakes have different scaling relationships from those of smaller earthquakes.

the application of the relations for the Thspunt PSHA is to assess the size of the characteristic earthquakes for fault sources, which are all in the moderate-to-large magnitude range. Therefore any systematic differences in the smaller magnitude range is not significant to our application in the SSC model.

Tanaka Geothermal gradient and heat

flow data in and around Japan

(II): Crustal thermal structure

and its relationship to

seismogenic layer

2004 The high-quality database of seismicity of Japan (JMA,

Japan Meteorological Agency) and an extensive

compilation of thermal measurements are used to quantify

the concept of temperature as a fundamental parameter for

determining the thickness of the seismogenic zone.

Qualitative comparisons between each data of heat flow

and geothermal gradient, and the lower limit of crustal

earthquake hypocentral distributions beneath the Japanese

Islands show that, as expected, the lower limit of seismicity

is inversely related to heat flow and geothermal gradient.

Gridded heat flow or geothermal gradient and D90, the

depth above which 90% of earthquakes occur, correlated

well with each other. The evaluated temperatures for D90

range between 250◦C and 450◦C except for higher heat

flow data. The consistency of temperature for D90 over a

large depth interval almost all over the Japanese Islands

support the concept that the temperature is the dominant

factor governing the focal depth in the crust.

Yes Provides a corroboration of physical models and constitutive models that correlate earthquake depths with crustal temperature. Provides an approach that can be used to assess the base of the seismogenic crust.

KC

Tanaka & Ishikawa Temperature at the base of the

seismogenic zone and its

relationship to the focal depth of

2002 Very similar to the data analysis and results presented in

Tanaka (2004). Essentially focusing on the heat flow

database and the thermal modeling to arrive at the depths

Yes (see Tanaka 2004) KC


110



SSC Model?



the western Nagano Prefecture

area

of various isotherms relative to the depth distribution of

seismicity.

Tinti & Mulargia Effects of magnitude

uncertainties on estimating the

parameters in the Gutenberg-

Richter frequency-magnitude

law

1985 The evaluation of the parameters in the Gutenberg-Richter

(GR) frequency-magnitude law log Nr = a − bm is shown to

be strongly affected by magnitude uncertainties. If the

magnitude errors are assumed to be distributed normally

with standard deviation σ, the observed magnitude that we

call the “apparent magnitude,” becomes a random variable,

and the frequency-apparent magnitude law differs from the

GR relation. However, the usual estimators for a are biased

by a quantity which is a quadratic function of the error

standard deviation σ and of β. This implies that the

apparent number, Na, of earthquakes exceeding a given

magnitude tends to be larger than the real number Nr and

for realistic values of a and b (or β), Na is expected to be

even as large as twice Nr.

Yes Indicates the need to assess recurrence taking into account the uncertainties in the magnitudes of each earthquake in the catalogue.

KC

USNRC Central and Eastern United

States Seismic Source

Characterization for Nuclear

Facilities

2012 Large regional seismic source characterization project for nuclear facilities in the central and eastern United States. The project was conducted using a SSHAC Level 3 approach and provides new or updated methodologies for defining seismic sources, characterizing their maximum earthquake magnitudes, assessing earthquake recurrence, and assessing future earthquake characteristics. Because the CEUS is a stable continental region, many of the methods and approaches given in this report are potentially applicable to the Thyspunt PSHA.

Yes Methods and approaches adopted or adapted for use on the Thyspunt PSHA include: CEUS earthquake focal depth distribution, updated Mmax prior distributions, approach to weighting alternative Mmax approaches, method for assessing recurrence including uncertainties in magnitudes and Mmax, models of temporal clustering

KC

USNRC Practical implementation

guidelines for SSHAC Level 3

and 4 hazard studies

2012 Regulatory guidance that defines the essential steps and detailed implementation guides for Level 3 and 4 studies. Provides the framework for the Thyspunt PSHA as a whole and for the detailed approaches used in the SSC data evaluation and integration processes.

No Methodologies presented are generic to any PSHA and do not contribute directly to the SSC model

KC

Van Lanen & Mooney

Integrated geologic and

geophysical studies of North

American continental intraplate

seismicity

2007 The correlation of North American stable continental region

earthquakes is examined using five geologic and

geophysical data sets: (1) a newly compiled age-province

map; (2) Bouguer gravity data; (3) aeromagnetic anomalies;

(4) the tectonic stress field; and (5) crustal structure as

revealed by deep seismic-reflection profiles. It is concluded

No No new information is presented that would change the Bayesian Mmax prior distributions significantly; the depth distributions for SCR come directly from global earthquake catalogues without analysis, so they appear to be contaminated by fixed depths and a range of quality.

KC


111



SSC Model?



that: (1) Archean-age (3.8–2.5 Ga) North American crust is

essentially aseismic, whereas post-Archean (less than 2.5

Ga) crust shows no clear correlation of crustal age and

earthquake frequency or moment release; (2) seismicity is

correlated with continental paleorifts; and (3) seismicity is

correlated with the NE-SW structural grain of the crust of

eastern North America, which in turn reflects the opening

and closing of the proto– and modern Atlantic Ocean. An

analysis of hypocentral depths for stable continental region

earthquakes shows that the frequency and moment

magnitude of events are nearly uniform for the entire 0–35

km depths over which crustal earthquakes extend. This is in

contradiction with the hypothesis that larger events have

deeper focal depths.

Wells &

Coppersmith

New empirical relationships

among magnitude, rupture

length, rupture width, rupture

area, and surface displacement

1994 Source parameters for historical earthquakes worldwide are

compiled to develop a series of empirical relationships

among moment magnitude (M), surface rupture length,

subsurface rupture length, downdip rupture width, rupture

area, and maximum and average displacement per event.

The resulting data base is a significant update of previous

compilations and includes the additional source parameters

of seismic moment, moment magnitude, subsurface rupture

length, downdip rupture width, and average surface

displacement. Each source parameter is classified as

reliable or unreliable, based on an evaluation of the

accuracy of individual values. Only the reliable source

parameters are used in the final analyses.

Yes Represents an extensive compilation of data and empirical regressions of magnitude-related rupture data, thus can be used for assessing moment magnitude for a given fault rupture dimension. Sufficient data numbers and ranges to define standard deviations and confidence intervals.

KC

Wesnousky Earthquakes, Quaternary faults,

and seismic hazard in California

1986 Data describing the locations, slip rates, and lengths of Quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in California. The expected seismic moment and the strength of ground shaking resulting from the entire rupture of each mapped fault (or fault segments) are estimated using empirical relations between seismic moment Mo, rupture

length, source to site distance, and strong ground motions. Assuming a fault model whereby the repeat time T of earthquakes equals the expected moment divided by the moment rate (which is proportional to fault slip rate), it is

Yes The maximum moment model is one alternative magnitude-frequency model for faults. It accounts for nearly all of the seismic moment associated with fault slip rates, but does not account for small-magnitude earthquakes occurring on faults.

KC


112



SSC Model?



observed that the moment-frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150-year historical record. The agreement is consistent with the argument that the geologic record of Quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in California. The author also concludes that a “maximum magnitude” model (later called a maximum moment model in subsequent publications) for individual faults is sufficient to account for all important earthquakes contributing to seismic hazard in California.

Wheeler Methods of Mmax Estimation

East of the Rocky Mountains

2009 Several methods have been used to estimate the magnitude of the largest possible earthquake (Mmax) in parts of the Central and Eastern United States and adjacent Canada (CEUSAC). Each method has pros and cons. The largest observed earthquake in a specified area provides an unarguable lower bound on Mmax in the area. Beyond that, all methods are undermined by the enigmatic nature of geologic controls on the propagation of large CEUSAC ruptures. Short historical-seismicity records decrease the defensibility of several methods that are based on characteristics of small areas in most of CEUSAC. Methods that use global tectonic analogs of CEUSAC encounter uncertainties in understanding what “analog” means. Five of the methods produce results that are inconsistent with paleoseismic findings from CEUSAC seismic zones or individual active faults.

Yes Provides a valuable inventory of available approaches for SCRs, including a consideration of the data that are available to exercise each approach; the approaches such as the Bayesian approach are said to hold the most promise, provided that the criteria for identifying proper analogue regions are well-defined.

KC

Wheeler Reassessment of Stable

Continental Regions of

Southeast Asia

2011 Probabilistic seismic-hazard assessments of the central and eastern United States (CEUS) require estimates of the size of the largest possible earthquake (Mmax). In most of the CEUS, sparse historical seismicity does not provide a record of moderate and large earthquakes that is sufficient to constrain Mmax. One remedy for the insufficient catalog is to combine the catalog of moderate to large CEUS earthquakes with catalogs from other regions worldwide that are tectonically analogous to the CEUS (stable continental regions, or SCRs). After the North America SCR, the largest contribution of earthquakes to this global SCR catalog comes from a Southeast Asian SCR that extends from Indochina to southeasternmost Russia. Integration and interpretation of recently published geological and geophysical results show that most of these Southeast Asian earthquakes occurred in areas exposing abundant alkaline igneous rocks and extensional faults, both of Neogene age (last 23 million years). The implied Neogene extension precludes classification of the areas as SCR crust. The extension also reduces the number of

No Although the proposed re-designation of parts of southeast Asia as non-SCR could have implications for the Bayesian approach to Mmax, no systematic check of his work has been made nor of the earthquake catalogue used.

KC


113



SSC Model?



moderate and large Southeast Asian historical earthquakes that are available to constrain CEUS Mmax by 86 percent, from 43 to six.

Working Group on California Earthquake Probabilities

Earthquake Probabilities in the

San Francisco Bay Region:

2002-2031

2003 This was a “community-based” activity under the auspices

of the US Geological Survey’s development of a “real-time”

assessment of the probability of large-magnitude

earthquakes on certain faults in the San Francisco Bay

Area. The recurrence behavior on the faults is modeled

using renewal models that take into account the elapsed

time since the most recent large earthquake on the fault,

the mean recurrence interval between large earthquakes,

and the standard deviation in the mean recurrence interval.

These types of non-Poissonian models are potentially

applicable to faults where sufficient paleoseismic data are

available.

No Although average fault slip rates are available for fault sources and an estimate of recurrence intervals for the Kango fault, all of the faults lack sufficient data to characterize renewal models

KC

Youngs &

Coppersmith

Implications of fault slip rates

and earthquake recurrence

models to probabilistic hazard

estimates

1985 Two models are considered to describe the partitioning of

the slip rate or seismic moment rate into various magnitude

earthquakes: an exponential magnitude distribution and a

characteristic earthquake distribution. Assuming an

exponential distribution, the activity rate, N(m°), is

constrained by the upper bound magnitude, mu, the b-value

for the region and the fault slip rate, S. For a given S,

variations in mu and b-value have significant effects on

recurrence and computed hazard, depending on whether

the assumption is made that the seismicity rate is constant

or the moment rate is constant. There is increasing

evidence that the characteristic earthquake model is more

appropriate for individual faults than the exponential

magnitude distribution. Based on seismicity data from areas

having repeated large earthquakes, a generalized

recurrence density function is developed, and the resulting

recurrence relationship requires only mu , b-value, and S, A

comparison of the recurrence relationships from this model

with the historical seismicity and paleoseismicity data on

the Wasatch and San Andreas faults shows a good match.

Yes Provides the functional form for the characteristic earthquake magnitude-frequency relationship, which has subsequently been shown to lead to reasonable matches with the combination of geologic slip rates, paleoseismic recurrence intervals, and seismicity that can be attributed to individual faults.

KC

Youngs et al. A comprehensive seismic

hazard model for the San

1995 A comprehensive seismic hazard model is presente for the San Francisco Bay rea for use in probabilistic analyses for earthquake hazards affecting the East Bay. The spatial

Yes The comparison of the predicted fault-specific recurrence rates with observed seismicity for the

KC


114



SSC Model?



Francisco Bay region distribution of seismicity for the region requires two types of seismic sources: fault-specific sources that represent mapped active strike-slip fault in the region, and distributed seismic zones that represent earthquake activity on minor faults and unmapped features between the major faults. Recurrence parameters are developed for all sources by converting crustal deformation rates (fault slip rates and fault-normal shortening rates) into seismic moment rates. The recurrence parameter estimated from seismcity is a regional b-value used to specify the slope of the exponentially distributed magnitudes. The levels of seismicity predicted from crustal deformation rates generally match the observed seismicity rates on both a source-by-source basis and for the Bay Area as a whole only when the characteristic earthquake model is used to define the magnitude-frequency distribution. The use of an exponential magnitude-frequency relationship for faults leads to gross overprediction of the rates of seismicity relative to the observed seismicity record.

characteristic earthquake and exponential models provides a basis for evaluating these alternative magnitude-frequency models.



115

References

Anderson, J.G. (1979). Estimating seismicity from geological structures for seismic risk studies.

Bulletin of the Seismological Society of America 69, 139-158.

Clark, D., McPherson, A. & Collins, D.C.N. (2011). Australia’s seismogenic neotectonic record:

A case for heterogeneous intraplate deformation: Record 2011/11. Geoscience Australia,

Canberra.

Collettini, C. & Sibson, R.H. (2001). Normal faults: normal friction? Geology 29, 927–930.

Gutenberg, B., & Richter, C.F. (1956). Earthquake magnitude, intensity, energy and

acceleration: Bulletin of the Seismological Society of America 46, 105-145.

Hanks, T., & Kanamori, H. (1979). A moment magnitude scale. Journal of Geophysical

Research 84, 2348–2350.Hanson, K.L., Slack, C., & Coppersmith, R. (2012b). Thyspunt

Geological Investigations—Kango Fault Study, Report No. 2012-0035, Rev. 0, Council for


Jackson, J.A., & White, N.J. (1989). Normal faulting in the upper continental crust: observations

from regions of active extension. Journal of Structural Geology 11, 15-36.

Johnston, A. C., K. J. Coppersmith, L. R. Kanter, & C. A. Cornell (1994). The Earthquakes of

Stable Continental Regions. Five vols. Report for Electric Power Research Institute (EPRI), Palo

Alto, CA, EPRI TR-102261.

Kafka, A.L. (2007). Does seismicity delineate zones where future large earthquakes are likely to

occur in intraplate environments? in Stein, S., and Mazzotti, S. (editors), Continental Intraplate

Earthquakes: Science, Hazard, and Policy Issues, Geological Society of America Special Paper

425, pp. 35-48, doi:10.1130/2007.2425(03).

Kafka, A.L., 2009, Use of Seismicity to Define Seismic Sources: Application to Eastern North

America: presentation given at CEUS SSC Project Workshop #2, February 18-20, Palo Alto,

Calif. www.ceus-ssc.com

Kijko, A. (2004). Estimation of the maximum earthquake magnitude, mmax. Pure and Applied

Geophysics 161, 1-27.



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Kijko, A. (2012). On Bayesian procedure for maximum earthquake magnitude estimation.

Research in Geophysics 2, 46-51.

Kijko, A., Graham, G., Singh, M., Roblin, D., & Brandt, M.B.C. (2009). Probabilistic PGA and

spectral acceleration seismic hazard maps for South Africa [abstract]: Invited lecture, Workshop

R1 ―Earthquake Hazard,ǁ the IASPEI General Assembly in Cape Town, January 11-16.

Klose, C.D., & Seeber, L. (2007). Shallow seismicity in stable continental regions. Seismological

Research Letters 78(5), 554-562.

Leonard, M. (2010). Earthquake fault scaling: Self-consistent relating of rupture length, width,

average displacement, and moment release. Bulletin of the Seismological Society of America

100, 1971–1988.

NAGRA (Nationale Genossenschaft für die Lagerung radioaktiver Abfälle) (2004). Probabilistic

Seismic Hazard Analysis for Swiss Nuclear Power Plant Sites (PEGASOS Project), Volume 1,

Final Report, Wettingen, Switzerland, July 31.

Petersen, M.D., Frankel, A.D., Harmsen, S.C., Mueller, C.S., Haller, K.M., Wheeler, R.L.,

Wesson, RL., Zeng, Y., Boyd, O.S., Perkins, D.M., Luco, N., Field, E.H., Wills, C.J., & Rukstales,

K.S., 2008, Documentation for the 2008 Update of the United States National Seismic Hazard

Maps: U.S. Geological Survey Open-File Report 2008–1128. 1-61.

Scholz, C.H. (1998). Earthquakes and friction laws. Nature 391, 37-42.

Schulte, S.M., & Mooney, W.D. (2005). An updated global earthquake catalogue for stable

continental regions: Reassessing the correlation with ancient rifts. Geophysical Journal

International 161, 707-721.

Schwartz, D.P., & Coppersmith, K.J. (1984). Fault behavior and characteristic earthquakes:

examples from the Wasatch and San Andreas fault zones. Journal of Geophysical Research 89,

5681-5698.

Stirling, M., Rhoades, D., & Berryman, K. (2002). Comparison of Earthquake Scaling Relations

Derived from Data of the Instrumental and Preinstrumental Era. Bulletin of the Seismological

Society of America 92(2), 812–830.



117

Tanaka, A. (2004). Geothermal gradient and heat flow data in and around Japan (II): Crustal

thermal structure and its relationship to seismogenic layer. Earth, Planets Space 56, 1195-1199.

Tanaka, A., & Ito, H. (2002). Temperature at the base of the seismogenic zone and its

relationship to the focal depth of the western Nagano Prefecture area. Journal of the

Seismological Society of Japan 55, 1-10.

Tinti, S., & Mulargia, F. (1985). Effects of magnitude uncertainties on estimating the parameters

in the Gutenberg-Richter frequency-magnitude law. Bulletin of the Seismological Society of

America 75, 1681-1697.

USNRC (2012a). Central and Eastern United States Seismic Source Characterization for

Nuclear Facilities. NUREG-2115, US Nuclear Regulatory Commission, Washington D.C.

USNRC (2012b). Practical implementation guidelines for SSHAC Level 3 and 4 hazard studies.

NUREG-2117, US Nuclear Regulatory Commission, Washington D.C.

van Lanen, X., & Mooney, W.D. (2007). Integrated geologic and geophysical studies of North

American continental intraplate seismicity: in Stein, S., and Mazzotti, S. (editors), Continental

Intraplate Earthquakes: Science, Hazard, and Policy Issues, Geological Society of America

Special Paper 425, 101-112.

Wells, D. L., & Coppersmith, K.J. (1994). New empirical relationships among magnitude, rupture

length, rupture width, rupture area, and surface displacement. Bulletin of the Seismological

Society of America 84, 974–1002.

Wesnousky, S.G., (1986). Earthquakes, Quaternary faults, and seismic hazard in California.

Journal Geophysical Research 91, 12587-12631.

Wheeler, R.L. (2009). Methods of Mmax Estimation East of the Rocky Mountains: U.S.

Geological Survey Open-File Report 2009-1018, 1-44.

Wheeler, R.L. (2011). Reassessment of Stable Continental Regions of Southeast Asia.

Seismological Research Letters 82, 971-983.

Working Group on California Earthquake Probabilities. (2003). Earthquake Probabilities in the

San Francisco Bay Region: 2002-2031: U.S. Geological Survey Open-File Report 03-214.



118

Youngs, R.R., & Coppersmith, K.J. (1985). Implications of fault slip rates and earthquake

recurrence models to probabilistic hazard estimates: Bulletin of the Seismological Society of

America 75, 939-964.

Youngs, R.R., Coppersmith, K.J., Taylor, C.L., Power, M.S., DiSilvestro, L.A., Angell, M.L., Hall,

N.T., Wesling, J.R., and Mualchin, L. (1992). A comprehensive seismic hazard model for the

San Francisco Bay region, in Borchardt, G. and others, eds. Proceedings of the Second

Conference on Earthquake Hazards in the Eastern San Francisco Bay Area. California

Department of Conservation, Division of Mines and Geology Special Publication 113, 431-441.


119

Table 3.5. Data Summary Table - Neotectonic Setting, Thyspunt PSHA.


Are the Data Used in the SSC

Model? Discussion of Potential Data Use GIS Code Originator

Tectonic Analogs

Bird et al. Plate Tectonics and Earthquake Potential of Spreading Ridges and Ocean Transform Faults

2002 Separates the Harvard CMT catalogue into spreading and transform earthquakes along ocean ridges.

Yes Agulhas Fracture Zone (8.4.2)

Mmax

M 7+ earthquakes on ocean transform faults

MEMA/

KLH

Boettcher & McGuire

Scaling Relations for Seismic Cycles on Mid-Ocean Ridge Transform Faults

2009 Develops a scaling relation for magnitudes of earthquakes on mid-ocean ridge transforms.


Magnitudes of largest events (6 < Mw < 7)

MEMA/

KLH

Bufe Stress Distribution Along the Fairweather–Queen Charlotte Transform Fault System

2005 This study models the stress distribution along the Fairweather–Queen Charlotte Transform by examining some of the historical earthquakes in the fault system.


M 8.1 Queen Charlotte Island earthquake

MEMA/

KLH

Clark et al. Australia’s Seismogenic Neotectonic Record: A Case for Heterogeneous Intraplate Deformation

2011 This study divides the Australian continent into six seismicity zones based on fault recurrence and behavioural characteristics based on palaeoseismological studies.

Kango Fault (8.4.1)

Episodic earthquake recurrence

MEMA/

KLH

Collettini & Sibson Normal Faults, Normal Friction? 2001 Compiles the dips from focal mechanisms of shallow, intracontinental, normal-slip earthquakes.

Yes Plettenberg Fault (8.4.4)

Generic distribution of dips

MEMA/

KLH

Crone et al. Episodic Nature of Earthquake Activity in Stable Continental Regions Revealed by Paleoseismicity Studies of Australian and North American Quaternary Faults

1997 In stable continental regions, faults show episodes of activity separated by quiescent intervals of at least 10,000 yr and commonly 1,000,000 yr or more. This study looked at Australian faults with historical surface faulting events (1986 Marryat Creek and 1988 Tennant Creek). The study also looked at the Meers and Cheraw Faults in the U.S.

Yes Kango Fault (8.4.1)


MEMA/

KLH

Crone et al. Paleoseismicity of Two Historically Quiescent Faults in Australia: Implications for Fault Behavior in Stable Continental Regions

2003 Examines the rupture history of the Roopena and Hyden Faults in South Australia. Both faults are in areas of limited to no seismicity but have evidence of multiple surface faulting events in the Quaternary.



MEMA/

KLH

Cronin Rates and Possible Causes of Neotectonic Vertical Crustal Movements of the Emerged Southeastern United States Atlantic Coastal Plain

1981 Evaluates the magnitude and rate of vertical crustal movement during the past 3 Myr in the U.S. Atlantic Coastal Plain of North and South Carolina. Palaeontologic evidence indicates a primary glacio-eustatic component to the local sea-level record and a secondary tectonic component. Net vertical uplift rates averaging 1–3 cm/kyr, but perhaps as high as 5–10 cm/kyr are in evidence for the emerged Coastal Plain (p. 830). General subsidence of 2–4 cm/kyr since the Cretaceous in submerged parts of the continental margin near subsiding sedimentary troughs. Hydro-isostatic crustal response to multiple deglaciation events may have periodically uplifted the coast, but long-term lithospheric flexural upwarping in response to sediment loading offshore is a more plausible mechanism to explain the present positions of shorelines above present mean sea level.

No Estimate eustatic sea level of +4 m for datum which corresponds to MIS 7.

p. 831 (and p. 825)—

Uplift rate may actually be overestimated because eustatic sea levels during Pliocene and early Pleistocene interglacials may have actually been higher than present sea level due to the contributions of glacio-eustasy and seafloor spreading to the local sea-level record. Since regression from Orangeburg Scarp, about 3 Ma, a eustatic sea-level drop of about 10–20 m would be expected from seafloor spreading.

-- KLH

EPRI et al. Central and Eastern United States Seismic Source Characterization for Nuclear Facilities

2012 Examines the recurrence interval and evidence for temporal clustering for nine faults in the Central and Eastern U.S. The faults studied are the Charlevoix, Charleston, Cheraw, Meers, Wabash Valley and four faults within the Reelfoot Rift zone—the New Madrid Fault System, the Eastern Rift Margin Fault, the Marianna Fault, and the Commerce Fault Zone.


Recurrence/Recency

MEMA/

KLH

Hanson et al. Style and Rate of Quaternary Deformation of the Hosgri Fault Zone, Offshore South-Central Coastal

2004 For a 70-degree or steeper dipping fault, an H:V ratio of approximately 1:8 or greater would suggest that the fault is a strike-slip fault.

Yes Style of faulting Agulhas Fracture Zone (8.4.2) MEMA/

KLH


120




California

Ishii et al. Mw 8.6 Sumatran Earthquake of 11 April 2012: Rare Seaward Expression of Oblique Subduction

2013 Discusses the tectonic setting of the 2012 M 8.6 Sumatran earthquake as related to oblique subduction.


Mmax

2012 M 8.6 Sumatran earthquake (not considered to be a good analogue for the AFZ)

MEMA/

KLH

Jackson & White Normal faulting in the Upper Continental Crust: Observations from Regions of Active Extension

1989 This study looks at earthquake foci of large normal faulting events and

concludes the dip range is between 30° and 60°.


Fault Geometry


MEMA/

KLH

Leonard Earthquake Fault Scaling: Self-Consistent Relating of Rupture Length, Width, Average Displacement, and Moment Release

2010 Proposes self-consistent scaling relations between seismic moment,

rupture area, length, width, and average displacement on a fault.


Mmax (empirical relationships)

MEMA/

KLH

Lamontagne Significant Canadian Earthquakes of the Period 1600-2006

2008 This study catalogs large, historical Canadian earthquakes including the 1946 M 8.1 Queen Charlotte Islands earthquake.


Mmax

M 8.1 Queen Charlotte Island earthquake

MEMA/

KLH

Satriano et al. The 2012 Mw 8.6 Sumatra Earthquake: Evidence of Westward Sequential Seismic Ruptures Associated to the Reactivation of a N-S Ocean Fabric

2012 Discusses the tectonic setting of the 2012 M 8.6 Sumatran earthquake. It concludes that the earthquake occurred in a diffuse zone of deformation.


2012 M 8.6 Sumatran earthquake (not considered to be a good analogue)

MEMA/ KLH

Wells & Coppersmith

New Empirical Relationships Among Magnitude, Rupture Length, Rupture Width, Rupture Area, and Surface Displacement

1994 Uses historical earthquakes to develop empirical relationships between

moment magnitude, surface rupture length, downdip rupture width, and

average surface displacement.



MEMA/

KLH

Wesnousky Displacement and Geometrical Characteristics of Earthquake Surface Ruptures: Issues and Implications for Seismic-Hazard Analysis and the Process of Earthquake Rupture

2008 Uses statistics on about three dozen historical earthquakes to compare

observations of surface slip along strike.



Tectonic Stress Regime

Altermann & Hälbich

Structural History of the Southwestern Corner of the Kaapvaal Craton and the Adjacent Namaqua Realm: New Observations and a Reappraisal

1991 Examines the structural history of the Kaapvaal Craton including up to seven phases of deformation during the Early to Middle Proterozoic.

Yes Earthquake recurrence intervals and slip rates

Andreoli Implications of Neotectonic Evidence in the Eastern Cape Region

2012 PowerPoint presentation. Slide 7: unpublished data of A. Logue from exploration data. Data show NNW orientation offshore of site.

No Seismotectonic setting (Chap. 4) MEMA/ KLH

Bird et al. Patterns of Stress and Strain Rate in Southern Africa

2006 This study used thin-shelled finite element modelling to explore potential causes of the Wegener Stress Anomaly (WSA). The model was constrained with data from the World Stress map and 17 additional Holocene direction/regime indicators (22 total data points).

The authors identified three potential causes of the WSA:

1. Lateral variations in density moment.

2. Resistance of unbroken lithosphere to plate rotation.

No Fig. 2 compiles all the stress data used in the study. The data are mostly in western South Africa and oriented NW-SE.

Seismotectonic setting (Chap. 4)

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3. Stress concentration ahead of a crack tip.

Concluded that WSA is primarily due to the resistance to the relative rotation between the Somalian and African Plates.

Calais et al. Kinematics of the East African Rift from GPS and Earthquake Slip Vector Data

2006 This study uses GPS and earthquake slip vector data to study kinematics of the East African Rift. Data is consistent with the following conditions:

1. Nubia-Somalia Euler pole between the southern tip of South Africa and the Southwest Indian ridge.

2. The existence of the Victoria microplate between the eastern and western rifts that is rotating counterclockwise with respect to Nubia.

3. Regional asthenospheric upwelling and locally focussed mantle flow influence deformation in eastern Africa.

The kinematic model proposed here, although consistent with the existing data, does not account for the widespread seismicity observed west of the Western rift.


Coppersmith & Neveling

Decision Memorandum Seismic Source Characterization Compensation Events Thyspunt PSHA

2009 This report processes data from 34 continuous GPS stations in South Africa; any station with a record less than 2.5 years long was excluded. The TRIGNET data from 1 January 2000 to 4 April 2009 was used. Velocities at these sites are best fit by a singular angular rotation, with deviations from rigid plate behaviour that do not exceed 0.4 mm/yr on average (max. 1.1 mm/yr at the northernmost station in eastern South Africa TDOU).

Strain rates for all triangles but one (ERAS-PTBG-TDOU) are 10−8

/yr or less and not significant at the 95% confidence level.

The strain rate pattern does not show any systematic behaviour that correlates with seismicity. In particular, the authors do not find evidence at this point for higher strain rates in northeastern South Africa, an area that may correspond to the southward continuation of the East African Rift. Nor do they find evidence for higher strain rates wrapping around the Kaapvaal craton, as proposed by Bird et al. (2006) from a mechanical modelling study.

No Fig. 6: Velocity with respect to Nubian Plate (5% confidence on error ellipses

Fig. 10: Principal horizontal strain rates

Table 4 lists all strain rates from triangles.


MEMA/ KLH

De Beer Tectonic Interpretation of the Ceres Earthquake Area and Implications to the Locations of Future Seismicity

2012 Slide 8: Summary of Stacey & Wesseloo (1998). Engineering and mining data for stress data.

No Stacey & Wesseloo data as presented in De Beer (2005)

MEMA/ KLH

De Beer Investigation into Evidence for Neotectonic Deformation Within Onland Neogene to Quaternary Deposits Between Alexander Bay and Port Elizabeth—South Coast Report

2005 p. 64— Prominent fractures of WNW-ESE orientations in the South and Southwest Cape were established during Early to Middle Cretaceous times. The 1969 earthquake showed that these fractures could be reactivated in the current stress field and that they are preferentially reactivated in the Ceres-Tulbagh area, but also host seismic events near Vanwyksdorp.

p. 72— Bedrock joints were not seen in most outcrops to propagate up into Cenozoic limestone. This may indicate that in general, very low strains, probably induced through slow regional uplift, are involved. The absence of well-developed sets of neotectonic joints in the Bredasdorp Group certainly does not give the impression that intense regional neotectonic stress of appreciable proportions is at work here.

p. 136— If the De Hoek Fault had been reactivated in the Quaternary in a normal faulting mode, it suggests that reactivation of E-W faults could occur along fault lines other than the CKBC fault system as well, and support the idea of

Yes Seismogenic probability of the Worcester Fault

The author could not demonstrate evidence of offset of Pliocene or Pleistocene deposits along the Worcester Fault.

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a current N-S extensional stress along the Southern Cape coastline.

De Beer Geology and Tectonics of the Thyspunt Site, Humansdorp

2000 Summarises the geological setting of the Thyspunt site. The study describes in detail the local structures at the Thyspunt site. The study recommends further neotectonic studies in the region.

No Seismotectonic setting (Chap. 4) MEMA

Hälbich Disharmonic Folding, Detachment and Thrusting in the Cape Fold Belt

1983 This study of the structures within the Cape Fold Belt notes that most decoupling occurs along the Nardouw Subgroup and the Cedarberg Shale.


Hälbich Cape Fold Belt Orogeny: State of the Art 1970s–1980s

1992 Summarises the present state of understanding of the Cape Fold Belt in 1992. Four episodes of deformation were dated at 278 Ma, 258 Ma, 247 Ma, and 230 Ma.


Heidbach et al. 2008 World Stress Map 2008 The world stress map data (Shmax) in regions south of the East African Rift are oriented NW. And near Cape Town, oriented E-W.


Delvaux & Barth African Stress Pattern from Formal Inversion of Focal Mechanism Data

2010 Focal mechanism data of 332 earthquakes in the African Plate are used to resolve the first- and second-order stress field of the East African Rift by formal stress inversion. In some cases, it is possible to resolve the third-order stress pattern as well.

In terms of stress orientations, the eastern part of the African Plate, which is dominated by the EARS, is affected by stresses with a general E–W orientation of horizontal principal extension (Shmin), while the Nubian Plate is affected by E–W horizontal principal compression (Shmax). While most of the rift basins that surround the Tanzanian craton display Shmin orientations roughly orthogonal to their trend, two dominant trends of Shmin are (1) WNW–ESE extension in the NW segments of EARS and in the SW High Plateau region and (2) ENE-WSW extension in the central part of the Western rift branch, the southern extremity of the Eastern rift branch, the southernmost rift segment, and the continental margin.

The tectonic stress regime observed shows some discrepancies with the modelled one. Normal faulting is found in conjunction with the broad uplifts associated with most of the rift, confirming the importance of the gravitational potential energy (PE) forces in the center of the continent. The low continental lands along the Indian coast and the Mozambique Channel portion of the Indian oceanic plate are affected by extensional faulting, while the Congo River Basin on the western side of the rift is characterised by a thrust faulting regime.

The second- and third-order stresses might show rapid lateral variations, probably reflecting a complex 3-D crustal structure and/or lithospheric plate architecture. Discrepancies that arise between these results and the stress pattern predicted by the models driven by gravitational PE forces only may suggest an overestimation of the continental PE forces in the models. Additional sources of tectonic stresses are necessary to explain the observed patterns. These might reflect deep processes like the spreading of a mantle plume head beneath the Tanzanian craton (Weeraratne et al., 2003) or mantle flow at the base of the lithosphere (Calais et al., 2006), or both.

No Neotectonic Setting and Tectonic Stress Indicators

The first–order stress pattern in continents is a consequence of plate boundary forces.

The second-order pattern might be related to intralithospheric processes and to the gravitational potential of topography.

• Large-scale extensional forces in eastern and southern Africa can be the action of gravitational PE within the plates (Stamps et al., 2010).

• As a consequence, in the absence of rifting, the stress field in the African Plate would be dominantly compressional, as Africa is surrounded by spreading oceanic ridges and an orogenic boundary to the north.

Mmax (EARS for comparison)

• 160 km long Kanda active normal fault between the Rukwa and the South Tanganyika depression may have generated the 1910 MS 7.4 earthquake, which is the strongest ever recorded in the East African rift (Vittori et al., 1997).

Future Earthquake Characteristics: Seismogenic thickness, fault dip, style of faulting

• Malawi Rift

Depth range: 10–29 km, with largest events at depths of 15–20 km.

Dip of normal faulting: 17°–50°.

• Central Mozambique (box 18)

Depth range: 12–30 km, with largest Mw 7.0 earthquake at depth of 12 km.

Dip: majority of normal faults are ~45°.

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Argus et al. Geologically Current Motion of 56

Plates Relative to the No-Net-Rotation

Reference Frame

2011 Updates DeMets et al. (2010) MOREVEL model by adding in an additional 31 small plates based on Bird (2003) bringing the total number of modelled plates to 56. These small plates constitute 2.8% of the earth’s surface. The addition of the 31 smaller plates has little effect on the motion of the 25 large plates.

Table 1 lists plate angular velocities.


Slip rate

MEMA/ KLH

Bird An Updated Digital Model of Plate

Boundaries

2003 Presents a digital set of global plate boundaries. The location of boundaries is based on topography, volcanism and/or seismicity. The plates include 14 large plates and 38 small plates for a total of 52 plates.

No MEMA/ KLH

Bird et al. Patterns of Stress and Strain Rate in

Southern Africa

2006 Uses finite element models to determine the cause of NW-SE-directed compression in South Africa and determine that it is mainly due to relative rotation between the Somalia and African Plates.

The article also postulates that seismic hazard in Namibia may be higher than the instrumental record suggests.

p. 12— The map of strain rates (Fig. 10) is strongly influenced by heat flow estimates.


Bird et al. Stresses That Drive the Plates from

Below: Definitions, Computational

Path, Model Optimization, and Error

Analysis

2008 Models 52 plates and divides the torque of each into lithostatic pressure, side strength, and basal strength. The study concludes that present plate motions on the earth appear to be driven primarily by deep mantle convection rather than by topography and associated lithostatic pressures.


De Mets et al. Geologically Current Plate Motions 2010 This study divides the surface of the earth into 25 tectonic plates. Yes Constraints on slip rate for the Agulhas Fracture Zone (8.4.2)


MEMA/ KLH

Hartnady Earthquake Hazard in Africa:

Perspectives on the Nubia-Somalia

Boundary

2002 Uses earthquake activity to divide southern Africa into regions of seismic belts and relatively stable seismic blocks.

Yes Figure 2 shows stable block boundaries (plate rates used to evaluate Agulhas Fracture Zone (8.4.2)


MEMA/ KLH

Hartnady Recent Motion of the African Plates 2003 Summarises the state of understanding of plate boundaries in southern Africa and maps zones of diffuse deformation between more stable blocks. It also summarises plate velocities relative to the International Terrestrial Reference Frame.


Horner-Johnson et al.

The Angular Velocity of Nubia

Relative to Somalia and the Location

of the Nubia-Somalia-Antarctic Triple

Junction

2005 Uses 103 ridge-perpendicular profiles across the Southwest Indian Ridge to determine the location of the triple junction of the Nubian, Antarctic, and Somalian Plates. The Nubia-Somalia angular velocity differs from the estimates of the Nubia-Somalia angular velocity from further north from the Gulf of Aden and Red Sea. Three hypotheses are considered to explain the difference in angular velocity:

1. Plate motion data have systematic errors.

2. The Nubian Plate is not a single rigid plate.

3. The Somalian Plate is not a single rigid plate.

The third hypothesis is preferred.

No MEMA/ KLH

Horner-Johnson et al.

Plate Kinematic Evidence for the 2007 Determines that models of plate motion have a better fit to spreading rates and transform fault azimuths if another plate exists between the Nubian and



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Existence of a Distinct Plate Between

the Nubian and Somalian Plates

Along the Southwest Indian Ridge

Somalian Plates. This plate, named the Lwandle Plate, is located between the Somalian, Nubian, and Antarctic Plates, mostly under the Indian Ocean.

Lemaux et al. Location of the Nubia-Somalia

Boundary Along the Southwest Indian

Ridge

2002 Deformation along the Nubian-Somalian Plate boundary south of 20°S is likely in a narrow ~100 km wide zone. The displacement along the Nubia-Somalia boundary over the past 11 Myr. is 23 km ± 6.6 km (95% confidence limits), indicating a displacement rate of 2 mm/yr.

Yes Algulhas Fracture Zone (8.4.2)

Recurrence

MEMA/ KLH

Martin & Hartnady Plate Tectonic Development of the

Southwest Indian Ocean: A Revised

Reconstruction of East Antarctica and

Africa

1986 Plate kinematic reconstructions indicate that tectonic activity at the South African margin ceased approximately 100 Ma.


Recurrence

MEMA/ KLH

Patriat & Parson A Survey of the Indian Ocean Triple

Junction Trace Within the Antarctic

Plate: Implications for Junction

Evolution Since 15 Ma

1989

Swath bathymetry mapping was used to determine the location and morphology of the Indian Ocean Triple Junction. Spreading rates are Southeast Indian Ridge 0.6–0.8 cm/yr half rate, faster spreading Central Indian Ridge (2–2.5 cm/yr) and the Southeast Indian Ridge (2.5–3 cm/yr).

No MEMA/ KLH

Reznikov et al. Structure of the Transkei Basin and

Natal Valley, Southwest Indian

Ocean, from Seismic Reflection and

Potential Field Data

2005 This study uses geophysical data from the southern Natal Valley and northern Transkei Basin to study the crustal structure. The crust is heterogeneous. Strong modifications of accretionary processes near ridge/fracture zone intersections may be a reason for such heterogeneity.

Yes Evidence for neotectonic activity related to the Nubia and Somalia Plates (8.4.2)

MEMA/ KLH

East African Rift

Chorowicz The East African Rift System 2005 This overview paper describes the structural organisation of the East African rift system (EARS). The most characteristic features in the EARS are narrow, elongate zones of thinned continental lithosphere related to asthenospheric intrusions in the upper mantle. The hidden part of the rift structure is expressed on the surface by thermal uplift of the rift shoulders. The paper (which summarises various mechanisms of formation of the EARS) presents a hypothesis of SE-ward relative divergent drifting of a not-yet-well-individualised Somalian Plate, in agreement with the existence of NW-striking transforms and transfer faults. The rifting propagated and is still developing southwards (due to the southward migration of the initial plume or other plumes The main phenomenon is formation of domes related to plume effect, weakening the lithosphere and, long after, failure inducing focussed upper mantle thinning, asthenospheric intrusion, and related thermal uplift of shoulders.

Information on the southernmost mapped extents of the EARS:

Western branch of Malawi rift: This rift is at an early stage of development. Asymmetric graben, major fault (dip 65° at surface becoming listric at depth) bordering western margin (7,000 m throw, assuming erosion has occurred); overall structure is that of a roll-over pattern dipping west, accompanying a unique major east-dipping fault along the western border. Depth to detachment depends on crust thickness, between 15 km and 30 km. The W–E width of the uplifted areas across the rift direction is ~300 km

No Neotectonic Setting of EARS and Plate Motion Models

Zones of weakness, including both crustal and mantle (including hot-spot tracks and lithospheric upwelling).

• Tentative lithospheric map of eastern Africa (Fig. 10) showing hypothesised Late Oligocene to present-day trajectory of a hot-spot curve.

Future Earthquake Characteristics

• Geometry of recognised Quaternary faults associated with the EARS and possible extensions to the south (Fig. 1).

• Fig. 10 shows sense of slip on faults. Fault bounding eastern side of Urema graben fault is down-on-the-west.

All the extensional faults in Malawi rift have the same 65°–70° eastward dip (based on seismic reflection profile data shown on Fig. 3). Fault becomes listric at depths of <30 km.

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(including rift shoulders that reach ~1,300 m higher than rift floor). The overall topographic surface is generally 500 m higher in the west than in the east of Lake Malawi, meaning the lithosphere is thicker in the west. This may correspond to a variation in lithospheric thickness inherited long after the Pan-African collision of two different lithospheric blocks.

West of Lake Malawi, the elongate Luangwa lowlands have a NNE strike and belong to the Karoo rift system. This basin, appended to the main EARS line, may have resulted from reactivation of the Karoo normal faults, with slight subsidence, but the drainage of the basin may be responsible for the lack of significant late Cenozoic sediments. There is no significant rift shoulder development. Other less-defined graben basins comprise Lake Kariba.

Southeastern branch: This branch is less developed than the northern branches. It comprises the Pemba, Mafia, Kerimbas, and Lacerda Basins, which are more than 20 km wide half-graben zones of normal faulting. They generally parallel the main trend of the margin and may have been favored by tendency to detachment of the margin sediments due to gravity forces. The Kerimbas and Lacerda Basins are possibly related to reactivation of ancient strike-slip faults of the Davie Ridge.

Contreras et al. Growth of a Normal Fault System:

Observations from the Lake Malawi

Basin of the East African Rift

2000 Discusses the growth history of the Usiya normal fault system, which bounds the west side of the northern Lake Malawi Basin. The basin has been actively subsiding since the Late Miocene and has a maximum depth of about 3 km. The paper summarises the temporal evolution of the fault system and presents a cumulative plot showing how the three segments increased their length and displacement over time.

No Regional Tectonic Setting (EARS)

Evidence for recent and/or repeated reactivation of pre-existing structures (four rift basins).

• This paper addresses the evolution of normal fault systems and provides a simplified structural map of the acoustic basement of the central part of the Malawi rift.

EARS Earthquake Recurrence

Northern Lake Malawi Basin—Constraints on slip rate: 3 km/~8.6 Myr = 0.35 mm/yr (minimum does not include rift shoulder uplift and erosion). Note that Steinbruch (2010) states that “the amount of subsidence is almost equal to the amount of uplift of the rift flanks above local topography (Ebinger, 1989; Contreras et al., 2000).”

KLH

Delvaux & Barth African Stress Pattern from Formal

Inversion of Focal Mechanism Data

2010 (See summary above under Tectonic Stress Regime.) Yes EARS Mmax and Future Earthquake

Characteristics

• 160 km long Kanda active normal fault between the Rukwa and the South Tanganyika depression may have generated the 1910 MS 7.4 earthquake, which is the strongest ever recorded in the East African Rift (Vittori et al., 1997).


• Malawi Rift

Depth range: 10–29 km with largest events at depths of 15–20 km.

Dip of normal faulting: 17°–50°.

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• Central Mozambique (box 18)

Depth range: 12–30 km, with largest Mw 7.0 earthquake at depth of 12 km.

Dip: Majority of normal faults are ~45°.

Dugda et al. S-Wave Velocity Structure of the

Crust and Upper Mantle Beneath

Kenya in Comparison to Tanzania

and Ethiopia: Implications for the

Formation of the East African and

Ethiopian Plateaus

2009 New estimates of the S-wave velocity structure of the crust and upper mantle beneath the Kenya rift and surrounding Kenya highlands have been obtained by jointly inverting P-wave receiver functions and Rayleigh wave phase and group velocities. The inversion results yield Moho depths beneath the rift and highlands that are consistent with previously reported estimates of crustal thickness. There is an indication of the presence of partial melt under the Kenya rift. There is little similarity between the lithosphere under the East African Plateau and the lithosphere under the Ethiopian Plateau. The lithosphere under the Ethiopian Plateau is thin, extending to a depth of no more than about 80–90 km. The maximum S-wave velocity in the lithosphere is also low, reaching only to 4.2–4.3 km/s, compared to 4.6–4.7 km/s beneath the Mozambique Belt in northern Tanzania and the Kenya highlands.The contrast between the two regions indicates that the buoyant support for the plateau elevation in East Africa, including the Kenya highlands, resides deeper in the mantle than beneath the Ethiopian Plateau.

No Regional Tectonic Setting (EARS)

Zones of weakness, including both crustal and mantle (e.g., hot-spot tracks and lithospheric upwelling)

Evidence for colder, deeper lithosphere in the southern part of the EARS.

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Dumisani Seismotectonics of Zimbabwe 2001 Summarises the seismotectonics setting of Zimbabwe based on instrumental seismicity for the period 1910–1991. Seismicity is confined to regions with broadscale lineaments that trend in a NE direction. High seismic hazard potential lies along the Deka fault zone mid-Zambezi Basin to the north and northwest of Zimbabwe, in the Save-Limpopo mobile belt to the south and along the Zimbabwe eastern highlands, bordering Mozambique.

The largest earthquake (magnitude 6.4) occurred in the mid-Zambezi Basin on 23 September 1963. From energy calculations a magnitude of 6.6 is obtained in the mid-Zambezi Basin and to the SE of Zimbabwe in Mozambique. Activity in the mid-Zambezi Basin is attributed mainly to reservoir-induced seismicity, but pre-reservoir earthquakes (e.g., MS 6 on 28 May 1910) support the existence of natural tectonics and seismic activity before the Lake Kariba dam was built.

Citing other authors, the report indicates that faulting is predominantly normal with tensile stresses directed in a NW-SE direction; southern African region is under a NW-SE extension normal to the direction of main lineaments; directions of the principal stresses in the region are similar to those that existed in the East African Rift from the Miocene period.

An MS 6 earthquake in 1940 occurred in southern Zimbabwe on the boundary of the Zimbabwe shield and the Save-Limpopo mobile belt; few small-magnitude events have since occurred in the vicinity of its epicenter.

No EARS Probability of Activity

Evidence for recent and/or repeated reactivation of pre-existing structures (four rift basins).

• Map of central southern Africa showing broad-scale lineaments and faults: shows possible lineaments across Botswana.

• Concentrated zone of observed seismicity—fault plane solutions.

Mmax

• Magnitudes of historical earthquakes (M 6.4, on 23 September 1963; MS 6 on 28 May 1910).

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Fenton & Bommer The Mw 7 Machaze, Mozambique,

Earthquake of 23 February 2006

2006 Describes the Mw 7 Machaze, Mozambique, earthquake of 23 February 2006, which is the largest earthquake to have occurred in Mozambique in historical time. The closest event of similar size was the M 6.8 event at the northern end of the Lake Malawi Basin in 1942. The paper summarises the tectonic setting: the western branch containing Lakes Tanganyika and Malawi terminates in central Mozambique. The eastern branch continues through Kenya and appears to terminate in southern Tanzania. Both branches are developed in Proterozoic mobile belts that have accreted to the margins of the Nubian shield and the Tanzanian craton. Extension

No Probability of Activity and Mmax

Evidence of geologically recent fault displacement—mapped fault with historical rupture:

• Maximum historical earthquake (Mw 7) and southern extent of EARS.

• Palaeoseismic indicators of M > 5 earthquakes

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marked by volcanic activity began ~45 Ma; faulting began about 30 Ma in Ethiopia and propagated south. The southern extent of the rift south of the Lake Malawi Basin and the eastern branch south of the Tanzania-Mozambique border are not well studied.

The geology and geomorphology of Mozambique indicate that the Urema and Dombe troughs may be the southern continuation of the western branch through northern Mozambique. Persistent seismicity in the Mozambique Channel indicates that the eastern branch continues to the south to intersect the Southwestern Indian Ridge (SWIR) somewhere between 26.3°E and 32.2°E. Current estimates of opening across the rift range from 8.3 ± 1.9 mm/yr in the Afar region at the northern end of the rift and 3.6 ± 0.5 mm/yr near the intersection with the SWIR (Horner-Johnson et al., 2005).

The surface rupture was developed in a broad, flat alluvial plain, with no apparent pre-existing fault-related geomorphology. However, examination of digital elevation data and remote sensing imagery has identified very subdued features, including vegetation lineaments and areas of ponded sediment that define a lineament along the trace of the surface rupture.

Recurrence

• Reports that current estimates of opening across the rift are 3.6 ± 0.5 mm/yr near the intersection with the SWIR (Horner-Johnson et al., 2005).


• Surface rupture of at least 15 km, with a possible overall extension of 30 km.

• Vertical separation from 0.4 to 2.05 m and a component of left-lateral displacement of max 0.7 m.

Hartnady Uplift, Faulting, Seismicity, Thermal

Spring and Possible Incipient Volcanic

Activity in the Lesotho-Natal Regions,

SE Africa: The Quathlamba Hotspot

Hypothesis

1985 Various features of the Lesotho-Natal region, including its anomalously high topographic elevation, the occurrence of numerous thermal springs, a few enigmatic CO2 gas exhalation sites, and a significant level of current seismicity in certain zones, are evidence for some Neotectonic activity. There are media reports of a small volcanic eruption in 1983. It has been suggested that a process of continental margin-parallel warping was in operation during the Plio-Pleistocene period to produce the apparent uplift and seaward tilting of older geomorphological land surfaces, but the fundamental geophysical cause of this process is unclear.

The late Tertiary anorogenic plateau uplift over a wider region of East Africa has been related to African Plate absolute motion of the African continent over the former position of the Indian Ocean spreading ridge, but this is expected to have occurred only in a mantle reference frame fixed to the South American Plate. Kinematic modelling of the postulated Lesotho-Natal (Quathlamba) hot-spot trajectory, using the other major hot spots as a mantle reference frame, shows a coincidence with a chain of volcanic seamounts in the Mozambique Basin. The model is untested with regard to showing a consistent decrease in age from NE to SW.

Yes Contemporary Seismotectonic Setting

Zones of weakness, including both crustal and mantle (e.g., hot-spot tracks and lithospheric upwelling).

Possible evidence for Neotectonic activity along a postulated hot-spot track.

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Keranen et al. Low Lower Crustal Velocity Across

Ethiopia: Is the Main Ethiopian Rift a

Narrow Rift in a Hot Craton?

2009 Presents results of joint inversion of receiver function waveforms and surface-wave dispersion curves in Ethiopia to model crust and upper mantle properties in the Main Ethiopian rift (MER) and the Ethiopian Plateau. The results show that the MER is a classic narrow rift that developed in hot, weak lithosphere. The region of hot lithosphere closely corresponds to the region of flood basalt volcanism. The authors infer that the volcanism and thermal perturbation were jointly caused by impingement of the Afar plume head ~30 Ma. Development of both the East African Rift System (EARS) in the south (in cold, strong lithosphere) and the MER to the north (in hot, weak lithosphere) as narrow rifts, despite vastly different initial thermal states and depth-integrated lithospheric strength, indicates that common models that focus only on temperature, thickness, and vertical strength profiles do not apply to these classic continental rifts. Inherited structure and associated lithospheric weaknesses are a primary control on the mode of extension.

No EARS—Contemporary Seismotectonic

Setting

Zones of weakness, including both crustal and mantle (e.g., hot-spot tracks and lithospheric upwelling).

Evidence for recent and/or repeated (four rift basins).

• Localisation of rifting along pre-existing structures (older suture zones like the Mozambique Belt, a Himalayan-type collisional zone) should be considered in characterising the potential for extension of the rift to the south of the Eastern and Western rifts structures as presently mapped.

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Off-axis Mio-Pliocene and Quaternary volcanism in the Ethiopian Plateau may reflect continued presence of melt far from the rift axis.

Kim et al. Crustal Velocity Structure of the

Rukwa Rift in the Western Branch of

the East African Rift System

2009 This paper presents results of analysis of thickness and seismic velocity structure of the Rukwa rift crust based on modelling of seismograms of the 1994 Mw 5.9 Rukwa earthquake and teleseismic receiver functions from two stations at the southern end of the rift. The results yielded two estimates of the Moho depth (34 ± 2, 38 ± 2). Best fitting velocity model of 4.5 km low-velocity zone (sedimentary basin fill) over a 33 km thick middle to lower crust section.

No EARS—Future Earthquake Characteristics: Seismogenic depth

Results suggest that at least some of the crust at mid- to lower-crustal depth is strong enough to support brittle deformation.

__ KLH

Kinabo et al. Early Structural Development of the

Okavango Rift Zone, NW Botswana

2007 Aeromagnetic and gravity data collected across the Okavango rift zone (ORZ), NW Botswana are used to map the distribution of faults, provide insights into the 2D shallow subsurface geometry of the rift, and evaluate models for basin formation as well as the role of pre-existing fabric on the development of a nascent continental rift. The strike of rift-related structures closely follows the structural fabric of Proterozoic basement terrane rocks. The pre-existing fabrics and structures represent a significant strength anisotropy that controlled the orientation of younger brittle faults within the stress regime present during initiation of the rift.

Three en-echelon NE-trending depocenters coincide with structural grabens that define the ORZ. The early rift stage is characterised by a synformal depression to early half-graben stage lacking a well developed border fault system. The ORZ is characterised by several NE-trending normal faults, many of which have surface expression in the Shuttle Radar Topographic Model 30 (SRTM-30), Digital Elevation Model Map. Boundary faults along the SE boundary of the rift accommodate most of the strain defining a 50 km wide zone of subsidence within a larger 150 km wide zone of forming a rift-in-rift structure.

No Probability of Activity of Tectonic

Features in Botswana

Evidence for recent and/or repeated reactivation of pre-existing structures:

• Early rift stage to early half-graben stage development

Evidence of geologically recent fault displacement

Characterisation of Fault Characteristics

• Table 1 gives vertical displacements and fault lengths)

• The two largest west-dipping faults on the SE margin of the ORZ are the Mababe (northernmost fault ,100 km long, throw = ~521 m) and Kunyere (southernmost fault, 325 km long, throw = 232–334 m),

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Macheyeki Fault Kinematics and Tectonic Stress

in the Seismically Active Manyara-

Dodoma Rift Segment in Central

Tanzania—Implications for the East

African Rift

2008 The Eastern branch of the East African Rift continues southward after the North Tanzanian divergence in a broad N-S-trending and active deformation zone, referred to as the Manyara-Dodoma rift segment. In a two-stage rifting model, most of the structures represent the southward expansion of the Eastern branch during the second rift stage, which is thought to have started 1.2–1.3 Ma. Vertical offsets on these new faults do not exceed 200–300 m.

No EARS—Probability of Activity of Tectonic

Features

Earthquake Recurrence

Slip budget for Eastern branch of rift in Tanzania. 200–300 m./1.2–1.3 Ma = 0.15–0.25 mm/yr.

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Moussa Spectral P-wave Magnitudes,

Magnitude Spectra and Other Source

Parameters for the 1990 Southern

Sudan and the 2005 Lake Tanganyika

Earthquakes

2008 Describes the characteristics of the Mw 7.1 Sudan earthquake of 20 May 1990 and the Mw 6.8 Tanganyika Lake earthquake of 12 December 2005. The epicenters are located in the southern Sudan and the central segment of the western branch of the East African Rift System (EARS). The fault plane solution of the Sudan earthquake, a complex rupture at the intersection of the northern and western branches of the East African Rift, shows sinistral strike-slip along a NW-SE-trending fault. The focal mechanism solution of the December, 2005 Tanganyika Lake earthquake is consistent with the current tectonics of the Tanganyika-Rukwa-Malawi (TRM) central rift segment, the western branch of the EARS. It reflects NNW-SSE dip-slip fault plane in which extension is directed E-W to ENE-WSW. The inferred tensional axis orientation, however, is perpendicular to the rift faulting and in a fair agreement with tensional axis deduced from the focal mechanisms of earthquakes, fault slip data, and the high-resolution

No EARS—Mmax

Characteristics of Future Ruptures

Provides information on the magnitude, and source parameters (maximum average spectral magnitude, seismic moment, average displacement, and stress drop). The values of the stress drops and the ambient stresses estimated for both events indicate that these earthquakes are of interplate type.

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reflection seismic data in the northern part of the lake. This extensional direction is in agreement with the ESE predicted direction of motion of the Somalia with respect to Nubia, based on the GPS data, indicating that the stress responsible for the rift structure is still active.

Raucoules et al. Surface Displacement of the Mw 7 Machaze Earthquake (Mozambique): Complementary Use of Multiband InSAR and Radar Amplitude Image Correlations with Elastic Modeling

2010 Discusses surface displacement related to the 2006 Machaze earthquake based on analysis of Synthetic Aperture Radar Interferometry (InSAR) and sub-Pixel correlation (SPC) of radar amplitude images. Measurements were recorded at three different stages of the seismic cycle (i.e., before, during, and after the earthquake).

Postseismic slip—Postseismic deformation seems to be constant with time, about 3.5 cm/year for at least the two years after the earthquake. Afterslip that occurs when coseismic stress changes is the best candidate source phenomenon to explain afterslip, as its direction is the same as that of the coseismic slip.

Inter-seismic slip—no pre-seismic motion on the fault that is high enough to be observed with conventional InSAR.

Coseismic deformation—The observed displacement ranges from 1.5–2 m (consistent with Fenton & Bommer, 2006) in the southern part of the rupture to 0.7–1.3 m in the northern section (consistent with Hashimoto et al., 2007), who proposed a smaller displacement on the northern segment.

Deformation also is observed NNW of the epicenter after the earthquake, but this is not explained and should be investigated.

No Location of Machaze Rupture GIS_S0012_F1

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Shumba et al. Focal Mechanism Solution of the 15 March 2008 Nyamandlovu Earthquake

2009 The focal mechanism of the 15 March 2008 Nyamandlovu earthquake (mb = 4.3; USGS M 4.7) that occurred~135 km NW of Bulawayo City, Zimbabwe (epicenter at 19.79°S and 27.39°E), is normal oblique left-lateral. This mechanism is similar to the events recorded in the Zambezi branch of the East African Rift. The preferred nodal plane has a strike of 55°, dip = 48°, rake = –95°. The NE-striking plane is preferred, based on the trend of lineaments from Botswana running northeasterly through Hwange and Kariba Gorge into Luangwa Valley, concentrations of epicenters of earthquakes trending along a northeasterly direction from Botswana into the Deka fault zone, Zambezi/Luangwa Valleys, and focal mechanism solutions obtained for the Lake Kariba area, ~150 km to the northeast. The earthquake had a shallow depth of 5 km (USGS depth of 5.8 km). Earthquakes in this region appear to be induced by pore-pressure differentials in underlying rock.

No EARS—Characteristics of Future

Ruptures

Evidence for potential zones of stress concentration/amplification and

Orientation of structures relative to underlying stress field (either favorable or unfavorable):

• Analysis of instrumental seismicity data (depths, focal mechanisms).

Table 1 presents information on felt earthquakes in the region from 1973 to 2008.

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Stamps et al. Lithospheric Buoyancy Forces in Africa from a Thin Sheet Approach

2010 Using a thin sheet approach and the CRUST 2.0 model, the authors compute vertically averaged deviatoric stresses arising from horizontal gradients of gravitational potential energy. Computed deviatoric stress directions agree well with earthquake focal mechanisms and stress indicators from the World Stress Map projects. This paper shows that buoyancy forces may account for a significant part of the force budget causing continental rifting but are likely insufficient to rupture an initially thick and cold continental lithosphere. This suggests that other processes contribute at a significant level to the force balance driving continental rifting in East Africa.

Seismicity in the East African Rift is moderate, with a few events slightly larger than M 7 and mostly extensional focal mechanisms. Albaric et al. (2008) show that earthquake hypocenters deepen from north to south along the Eastern rift from 10 to 20 km, whereas they are usually deeper along the Western rift (up to 35 km). Albaric et al. (2008) argue that this depth


Recurrence-constraints on rates of plate motion

EARS—Contemporary Seismotectonic

Setting

Zones of weakness, including both crustal and mantle (e.g., hot-spot tracks and lithospheric upwelling):

• The African continent is overall under tensional deviatoric stresses, reaching up to 15 MPa in the northernmost part of the East African Rift, decreasing to about 5 MPa at the

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distribution is consistent with tectonic provinces (contrasted thermal gradients and basement types) and implies a highly resistant, mafic lower crust.

Recent analysis of geodetic data and earthquake slip vectors in East Africa show that (1) present-day Nubia-Somalia motion is consistent with the ~3 Myr average, (2) the kinematics of the plate boundary zone is best described with a model that includes three minor sub-plates defined using the distribution of seismicity (Victoria, Rovuma, and Lwandle), and (3) extension is directed ~E-W along the rift, with rates decreasing from 6–7 mm/yr in the Main Ethiopian Rift, to 3–4 mm/yr in the central East African Rift, to <1 mm/yr south of Mozambique. The Nubian Plate behaves rigidly at the current precision level of the GPS measurements.

High topography surrounding the East African Rift corresponds to crustal thicknesses between 30 and 35 km, less than the average for the continent.

southern termination of the Malawi rift. Deviatoric stress magnitudes are high outside of the East African Rift as well, in particular in the southern part of the continent, and may explain the off-rift seismicity observed throughout Africa.

• Principal tensional deviatoric stresses along the active Mweru rift, Kariba graben, and Okawango faults are oriented NW-SE perpendicular to these structures, which could explain normal faulting and incipient rifting these regions. Calculations also predict compressional deviatoric stresses consistent with observations of reverse focal mechanisms along Africa’s passive margins offshore Mauritania and in the Gulf of Guinea.

• Deviatoric stresses result largely from the high elevations of southern and eastern Africa, a feature that possibly results from mantle flow associated with the African Superplume (Conrad & Gurnis, 2003). (See summary under uplift rates.)

High strain rates in contemporary tectonic setting:

• Paper summarises regional rates of extension.


• Rates decreasing from 6 to 7 mm/yr in the Main Ethiopian Rift, 3–4 mm/yr in the central East African Rift, to <1 mm/yr south of the Malawi rift.

Specht & Rosendahl

Architecture of the Lake Malawi Rift, East Africa

1989 Provides a description of the various segments of the Malawi rift based on interpretation of multichannel seismic data.

The Malawi rift in the northern rift zone of the southern branch of the East African rift system extends for more than 700 km from the Tukuyu graben in the north through the Shire valley in the south. The dominant style of “normal” fault systems in the rift is roughly N–S, indicating that extension is approximately E–W over much of the rift zone. The amount of extension estimated in the upper crust is small, probably about 7% or 3.5 km for the northern half of the rift, but given uncertainties in the true direction of extension, may be slightly higher. The relief of rift shoulders appears to correlate with the degree of subsidence and rift development. Because subsidence and sediment accumulation are greatest in the northern three half-graben units, and because the rift mountains tend to have the greatest relief opposite the border faults of these units, it is assumed that the northern half of the rift is older and more structurally mature than the southern half. Sediment thickness in the southern part of the rift (the Mwanjage and Mtakataka half graben) is ~1 km. There are limited seismic data for these half-graben units, but the associated basins appear to be very recent.

No EARS-Probability of Activity of Tectonic

Feature

Evidence of geologically recent fault displacement.

Future Earthquake Recurrence

• Provides detailed map of structures within the Malawi rift (Plate 2).

• Estimates of extension (3.5 km in the north), decreasing sediment thickness, and rift shoulder development to the south.

Minimum throw of the northernmost half-graben border fault is 3.5 km; total relief exceeds 5 km. Sediment thickness at south end is ~1 km.

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Steinbruch Geology and Geomorphology of the Urema Graben with Emphasis on the Evolution of Lake Urema

2010 Discusses the geomorphology of the Urema graben, which is the southern part of the East African Rift System (EARS). The paper also summarises the tectonic setting of the East African Rift and Urema graben (UG). The

No EARS—Contemporary Seismotectonic

Setting

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UG is part of the western branch of EARS. Further south the UG branches into the Chissunga graben to the east and to the west into the Lucite/Dombe-Buzi-Limpopo fault zone (Vail, 1968; Chorowicz, 2005). The development of the UG began in the Eocene by reactivating an older tectonic zone. The active Zambezi rift acts as a dextral intracontinental transform fault that connects the UG with the Malawi rift (Chorowicz, 2005).The rift has an asymmetric shape towards the east. The eastern side was uplifted, and the hanging wall was removed by erosion. There are no data available about the amount of uplift or vertical throw for the UG. A decrease is observed from the Malawi rift with 6 km downdrop to less than 1 km in the Shire rift (adjacent to the UR) (Ebinger et al., 1984; Specht & Rosendahl, 1989). It is therefore speculated that sediment thickness in the UR is on the order of 1–6 km.

The UG is characterised by frequent seismic activity in magnitudes between 4 and 8 (Fig. 3 shows a magnitude 7 to 8 earthquake in the southern part of UG) and depths of epicenters of mostly between 26 and 33 km. The Centroid Moment Tensor focal mechanism indicates an E–W expansion (ANSS database).

Probability of Activity of Tectonic Feature

• Evidence of geologically recent fault displacement.


Slip Rate Constraints

• Comparison to Shire rift suggests downdrop of 1 km, but could be higher.

Vittori et al. Kanda Fault: A Major Seismogenic Element West of the Rukwa Rift (Tanzania, East Africa)

1997 The NW-SE-trending Rukwa rift links the N-S-oriented Tanganyika and Nyassa (Malawi) depressions. No major activity during the Late Quaternary has affected the main faults bordering the rift (the Lupa and Ulfipa escarpments), which do display faceted spurs and oversteepening at the base of the scarps, suggestive of some Middle–Late Quaternary activity. The epicenter of the 1910 M = 7.4 earthquake (historically the largest felt in Africa) was located near the Kanda fault, which affects the Ufipa plateau. This fault reactivates an old (Permian-Triassic?) strike-slip fault. The geomorphic expression of the Kanda fault is a prominent fresh-looking scarp more than 180 km long, dipping NE. No evidence for horizontal slip was observed. The height of the scarp progressively decreases towards the NW, from about 40–50 m to a few metres north of Sumbawanga. Faulted lacustrine deposits were dated 8,340 ± 700 and 13,600 ± 1,240 radiocarbon years. These low-energy deposits now hang more than 15 m above the present valley floor, suggesting rapid uplift during the Holocene. A vertical slip rate in the Holocene of at least 2 mm/yr is inferred from these data.

No EARS—Earthquake Recurrence

Slip rate budget for segment of the western branch of the EARS north of the Malawi rift (≥2 mm/yr, Holocene rate).

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Wichura et al. Evidence for Middle Miocene Uplift of the East Africa Plateau

2010 Provides a summary of Cenozoic uplift chronology, vegetation changes, and early hominin evolution in East Africa (Fig. 5). Onset of important volcanic activity and rifting, Pliocene rift flank uplift are indicated on a transect from northern Kenya to northern Tanzania (showing both eastern and western branch activity). The results show that there was significant relief along the East African Plateau prior to rifting based on mapping of a ~300 km long lava flow (13.4 Ma Yatta phonolite flow).

No EARS—Tectonic Setting

Suggest precursory uplift prior to rifting.

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Yang & Chen Mozambique Earthquake Sequence of 2006: High-Angle Normal Faulting in Southern Africa

2008 The fault plane for the February 2006 Mw 7.0 earthquake appears exceptionally steep, dipping 76°+.

No Future Earthquake Characteristics: Focal Mechanism

Consider steep fault dip in range of values for fault sources.

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Nubia-Somalia Plate Boundary

Bilham et al. Secular and Tidal Strain Across the Main Ethiopian Rift

1999 Uses laser ranging and GPS data from 1969 to 1997 to determine the relative motions of the Nubia and Somalia Plates in Ethiopia and determine the velocity is 4.5±1 mm/yr at N108±10E.

No Seismotectonic setting (Chap. 4)

MEMA

Calais et al. Kinematics of the East African Rift 2006 Uses an updated GPS and earthquake slip vector data set to estimate the No Regional Tectonic Setting—Plate motion GIS KLH


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from GPS and Earthquake Vector Data

Somalia-Nubia angular velocity, and proposes a first-order kinematic model for present-day deformation in the East African Rift. The data are consistent with (1) a present-day Nubia-Somalia euler pole located between the southern tip of Africa and the Southwest Indian ridge and (2) the existence of a distinct microplate (Victoria) between the Eastern and Western rifts, rotation counterclockwise with respect to Nubia. Geodetic and geological data also suggest the existence of a (Rovenna) microplate between the Malawi rift and the Davie Ridge, possibly rotating clockwise with respect to Nubia.

The data indicate that the East African Rift comprises at least two rigid lithospheric blocks bounded by narrow belts of seismicity (<50 km wide) marking localised deformation rather than a wide zone of quasi-continuous, pervasive deformation.

Based on this new kinematic model and mantle flow directions interpreted from seismic anisotropy measurements, the authors propose that asthenospheric upwelling and locally focussed mantle flow may influence continental deformation in East Africa.

models



High strain rates in contemporary tectonic setting.

• 2–5 mm/yr, or 40 to 100% of the total Somalian-Nubian plate motion, is accommodated by extension across the Western rift, with present-day rates increasing N–S.

• Conversely, 3.5 to 1 mm/yr or 60 to 20% of the total Somalian-Nubian plate motion, is accommodated across the Eastern rift, with rates decreasing N–S.

• Fig. 3b shows the rate along the transform south of –30°S to be ~2 ± 1 mm/yr.

• This model does not attempt to account for the widespread seismicity west of the Western rift, but does provide some overall constraints on maximum slip across southwestern branch (as defined by Kinabo et al., 2007).

• The relative motion between the Zambian craton and the stable Nubian Plate is less than the residual velocity at ZAMB or ~1 mm/yr.

• Both HRAO and RBAY are separated from stable Nubia by the seismically active Okavango rift in Botswana and the Senqu seismic belt in South Africa and Lesotho and may lie on a microplate separate from Nubia and Somalia (the Transgariep block of Hartnady, 2002).

S0011_F3a

GIS S0011_F3b

Ebinger et al. Rift Deflection, Migration, and Propagation: Linkage of the Ethiopian and Eastern Rifts, Africa

2000 Examines the portion of the East African Rift Zone where the Main Ethiopian and Eastern Rifts overlap. The anomalous breadth of the zone is a consequence of rift propagation and migration, rather than basin-and-range–style extension; both the Main Ethiopian rift and Eastern rifts have propagated along north-south lines, and the Eastern rift has migrated ∼200 km eastward since late Oligocene time.


Lemaux et al. Location of the Nubia-Somalia Boundary Along the Southwest Indian Ridge

2002 South of ~20°S, expression of deformation or seismicity due to the relative motion between the Nubia-Somalia boundary vanishes or is extremely subtle. Analysis of the locations of the old edge of magnetic anomaly 5 (which is over 11 Ma seafloor), shows that the main locus of deformation between the two plates near the Southwest Indian Ridge over the past 11 Myr can be no wider than a few hundred kilometers, from ~100 km west of the Du Toit Fracture Zone to ~50 km east of the Andrew Bain fracture zone complex. Deformation is most likely concentrated along a closely spaced set of fracture zones known collectively as the Andrew Bain fracture zone complex, which is only ~100 km wide. The displacement along this boundary over the past 11 Myr is 23 km ± 6 km (95% confidence limits), indicating a displacement rate of 2 mm/yr, much slower than typical rates of seafloor spreading and subduction.


Neotectonic Setting—Plate Motion

models

• Pole of rotation between Nubian and Somalian Plates.


Strain rate for Andrew Bain fracture zone in contemporary tectonic setting.

• Long-term slip rate of ~2 mm/yr over the past

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11 Ma.

Future Earthquake Characteristics:

Seismogenic thickness, fault dip, style of

faulting

Active strike-slip boundary between Nubian and Somalian plates along the Andrew Bain fracture zone.

Royer et al. Motion of Nubia Relative to Antarctica Since 11 Ma: Implications for Nubia-Somalia, Pacific-North America, and India-Eurasia Motion

2006 Revised estimates of rotation (relative to Lemaux et al., 2002) indicates a displacement of Somalian plate relative to Nubian Plate of 129 ± 62 km, 90 ± 42 km, and 52 ± 21 km over the past 11.03 million years, near the northern extremity of the East African Rift, the northern Mozambique Basin, and the Andrew Bain fracture zone complex, respectively. This corresponds to opening rates of 12 ± 6 mm/yr, 8 ± 4 mm/y, and 5 ± 2 mm/yr, which are comparable to rates over the past 3.16 My of 8 ± 3 mm/yr, 6 ± 2 mm/yr, and 4 ± 1 mm/yr indicated by the angular velocity of Horner-Johnson et al. (2005) Within uncertainties predicted rates are compatible with velocities estimated from space geodesy (from 7 mm/yr in the Ethiopian rift to 2 mm/yr closer to the Nubia-Somalia-Antarctica triple junction.

No Neotectonic Setting—Plate motion

models


Andrew Bain fracture zone

• Long term (post-11.03 My = 5 ± 2 mm/yr,0

• Post-3.16 My = 4 ± 1 mm/yr



faulting

Large right-lateral component of shearing, as the Nubia-Somalia boundary approaches the Southwest Indian ridge.

KLH

Focal Mechanisms/Seismicity

Albini Investigating the Past Seismicity of the Eastern Cape Province, South Africa

2012 This study for the Thyspunt Project examines seismicity in the Thyspunt Region. The largest event was the 1932 Mw 5.7 Grahamstown event.


MEMA

Albini et al. Tools for Compiling the Global Earthquake History. GEM Project Presentation, Global Earthquake Model

2012 This project aims to compile historical earthquakes from AD 1000 to 1903 of M > 7. The study compiles published earthquake reports including 994 earthquakes from 236 studies.


MEMA

Ambraseys & Adams

Reappraisal of Major African Earthquakes, South of 20°N, 1900–1930

1991 Re-examines those earthquakes in Africa south of 20°N, in the period 1900–1930 for magnitudes greater than 5.75.


MEMA

Ayele & Kulhánek Reassessment of Source Parameters for Three Major Earthquakes in the East African Rift System from Historical Seismograms and Bulletins.

2000 This study examines three earthquakes from the East African Rift, in 1906, 1910, and 1928.


MEMA

Midzi et al. Seismic Hazard Assessment in Eastern and Southern Africa

1999 Calculates the probabilistic seismic hazard for Eastern and Southern Africa, making maps of the 10% exceedance in 50 and 100 years.


Saunders et al. Seismicity of Southern Africa During 2006 with Special Reference to the Mw 7 Machaze Earthquake

2010 This paper, which discusses earthquakes in Southern Africa, notes that the most significant earthquake occurred in the southernmost extension of the East African Rift System and was a Mw 7. The observed fault geometry (normal faulting with a west-dipping fault plane) supports the moment-tensor solution calculated by Harvard with a nodal plane dipping 67°W and

Yes Future Earthquake Characteristics: Fault

dip, style of faulting

Machaze earthquake–strike 168°, dip 67°W

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striking 168° (Fenton & Bommer 2006).

Several tectonic earthquakes (101), however, did occur in South Africa

during the period of review, the largest being an earthquake off the coast

measuring 3.8 on the local Richter magnitude. A concentration of

earthquakes (8 total) was recorded in southern Lesotho, while a cluster of 9

earthquakes located in the Ceres area. Smaller clusters of activity were

recorded in KwaZulu-Natal (Vrede area), Free State (Koffiefontein and

Vryheid area) and the Northern Province (Pofadder area).

Yang & Chen Mozambique Earthquake Sequence of 2006: High-Angle Normal Faulting in Southern Africa

2008 Presents source mechanisms for the six largest shocks of the Mozambique earthquake sequence of 22 February 2006 that occurred along a N-S-trending zone of more than 50 km in length. The main shock is one of the largest (Mw ~ 7.0) to occur in Africa over the past 100 years and its P waveforms show that the N-S-trending normal faulting near the surface continues to depths of more than 15 km along an exceptionally steep dip of 76° ± 4°. When combined with a minor component of left-lateral slip observed in the field, indicate the rake to be between –80° and –89°; the minor amount of left-lateral slip observed on the ground appears to be less than 2% at depth. Results favor the Euler pole between the Somalian and Nubian Plates to lie southward of the epicenters.

No Mmax

• Length of historical Mw ~ 7.0 rupture = 50 km.



faulting

• Normal faulting with steep dip of 76° ± 4°.

• Seismogenic depth = midcrustal down to 15 km for 2006 main earthquake (Fig. 1 shows additional focal depths in region down to 25–30 km at and south of latitude 16°S).

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Mantle Processes and Lithospheric Properties

Brandt et al. Upper Mantle Seismic Structure Beneath Southern Africa: Constraints on the Buoyancy Supporting the African Superswell

2012 Examines SH-wave velocities under the Kalahari Craton and concludes the velocity under the craton is similar to the under other shields. The results suggest that there may be a thermal or chemical anomaly in the mantle transition zone, or alternatively that the shear wave velocity structure of the transition zone in global reference models needs to be refined. Overall, the seismic models provide little support for an upper mantle source of buoyancy for the unusually high elevation of the Kalahari craton, and hence the southern African portion of the African Superswell


Conrad & Gurnis Seismic Tomography, Surface Uplift, and the Breakup of Gondwanaland: Integrating Mantle Convection Backwards in Time

2003 Presents results of a model (backwards integrated) of the history of mantle flow based on a tomographic image of the mantle beneath southern Africa as an initial condition while reversing the direction of flow and analytically incorporating cooling plates as a boundary condition.

The model predicts that the large seismically-slow and presumably hot structure beneath southern Africa produced 500–700 m of dynamic topography throughout the Cenozoic. Since ~30 Ma, uplift has moved from eastern to southern Africa, where uplift rates are ~10 m/Myr, consistent with observations.

During the Mesozoic, the modelled topographic high is situated near Gondwanaland rifting, raising the possibility that this buoyant structure may have been involved with this breakup.

The high topography of Africa stretches farther to the north and south than the model prediction: much of the higher topography in eastern Africa is probably not dynamic topography, but rather, is related to volcanic activity and rifting that began in eastern Africa ~30 Ma.

No Neotectonic Setting


• Zones of weakness, including both crustal and mantle (e.g., hot-spot tracks and lithospheric upwelling):

• Time history of mantle upwelling beneath southern Africa.

Dynamic topography at present shows decreasing gradient form 0.4–0.5 km (NE part of South Africa) to less than 0.2 km in SW part of South Africa).

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Jacobs et al. The Kalahari Craton During the Assembly and Dispersal of Rodinia

2008 Summarises what is known about the dimension, geometry, architecture, and location of the Kalahari Craton within Rodinia.


Morgan Hotspot Tracks and the Early Rifting of the Atlantic

1983 States that hot-spot tracks are zones of weaker crust that may be exploited during rift initiation. Also hypothesises that hot-spot-induced uplift may result in erosion and the exposure of continental shields.


Ni et al. Sharp Sides to the African Superplume

2002 This study images the margins of the African Superplume with SKS phases. The study indicates that the boundary of the anomaly is sharp with a width less than 50 km. Dynamic models that fit the seismic constraints have a dense chemical layer within an upwardly flowing thermal structure. The tilt suggests that the layer is dynamically unstable on geological time scales.


Pérez-Gussinyé et al.

Effective Elastic Thickness of Africa and Its Relationship to Other Proxies for Lithospheric Structure and Surface Tectonics

2009 The effective elastic thickness (Te), of the lithosphere is a proxy for lithospheric strength. This paper presents a new Te map of the African lithosphere estimated from coherence analysis of topography and Bouguer anomaly data. The latter data set derives from the EGM 2008 model, the highest-resolution gravity database over Africa, enabling a significant improvement in lateral resolution of Te.

The analysis finds that Te is high, ~100 km, in the West African, Congo, Kalahari, and Tanzania cratons. Of these the Kalahari exhibits the lowest Te. Based in part on published seismic and mineral physics constraints, it is suggested that this may reflect modification of Kalahari lithosphere by anomalously hot asthenospheric mantle. Similarly, the Tanzania craton exhibits relatively lower Te east of Lake Victoria, where a centre of seismic radial anisotropy beneath the craton has been located and identified with a plume head, thus suggesting that low Te in this region also reflects modification of cratonic lithosphere by an underlying hot mantle. The lowest Te in Africa occurs in the Afar and Main Ethiopian rifts, where lithospheric extension is a maximum. In the western Ethiopian Plateau, a local Te minimum coincides with published images of a low P and S seismic velocity anomaly extending to ~400 km depth. The Darfur, Tibesti, Hoggar, and Cameroon line volcanic provinces are characterised by low Te and no deep-seated seismic anomalies in the mantle. Corridors of relatively low Te connect these volcanic provinces to the local Te minima within the western Ethiopian Plateau. The low Te is interpreted to indicate thinner lithosphere within the corridors than in the surrounding cratons. These corridors may provide potential conduits for hot asthenospheric material to flow from the western Ethiopian Plateau to the volcanic provinces of central and western Africa.

Yes

(indirect-ly)

Seismogenic Thickness

The effective elastic thickness, Te, is an alternative measure of lithospheric properties. The effective elastic thickness corresponds to the thickness of an idealised elastic beam that would bend similarly to the actual lithosphere under the same applied loads (Watts, 2001).

Although Te does not represent an actual depth to the base of the mechanical lithosphere, its spatial variations reflect relative lateral variations in lithospheric mechanical thickness.

Africa has been practically stationary within the hot-spot reference frame during the last 30 Myr (Morgan 1983), leading to long-lived interactions between hot upwellings in the mantle and the lithosphere (Burke 1996).

KLH

Seismotectonic Source Models

Brandt Review of the Seismotectonic Provinces and Major Structures in South Africa with New Data

2008 Summary of published seismotectonic models for South Africa (Partridge, Hartnady, and Du Plessis).

Yes Postulated Seismotectonic Zones

Considered in Identifying Source Zones

Provides alternative source zonations based on varying seismotectonic models. No estimates for Mmax or recurrence provided for postulated sources related to extension of East African Rift to the south.

KLH

Hartnady Seismotectonic Provinces of South Africa: Critical Review and New Proposals

1996 Identifies seismotectonic provinces for eastern and southern Africa. Defines zones based on seismicity and concepts of microplates within a wide Nubian-Somalian plate boundary.

Yes Provides a basis for defining zones related to the hot-spot track (Kwahlamba province, zone B1) and the Mozambique belt, zone B2).

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GIS_D0010

Hartnady Earthquake Hazard in Africa: Perspectives on the Nubia-Somalia Boundary

2002 Discusses the wide plate boundary between the Nubian and Somalian Plates that extends through eastern and southern Africa. The observed pattern of earthquake activity divides this region into seismic belts surrounding relatively stable aseismic blocks (i.e., the Ukerewe Nyanza [formerly known as the Victoria Plate] and Rovuma microplates. The differentiation of the Transgariep and Lwandle blocks is less well demonstrated due to the slow rates of plate motion.

A new method of estimating maximum magnitude based on the principle of seismic moment conservation requires that the rates and directions of motion of the major plates and the boundary zone blocks be known with sub-mm/yr accuracy.

No Neotectonic Setting

Seismotectonic Setting (Chap. 4)

Slow rates of plate motion between Transgariep and Lwandle block.

EARS Mmax

Mmax for Malawi rift—Jackson & Blenkinsop (1997) present geologic evidence for a prehistoric earthquake of magnitude 8 on the Bilala-Mtakataka Fault in southern Malawi.

-- KLH

Uplift Mechanisms (Partridge & Maud)

King Canons of Landscape Evolution 1953 Proposes that landscapes are formed through scarp retreat and pedimentation.

No Considered in Seismotectonic Setting

(Chap. 4)

MEMA

King The Morphology of the Earth: A Study and Synthesis of World Scenery

1962 Expands upon King (1953) and interprets the morphology of the earth and based on two central themes—pediplanation and continental drift. Pediplanation is initiated by regional uplift.


(Chap. 4)

MEMA

Partridge & Maud Geomorphic Evolution of Southern Africa Since the Mesozoic

1987 Develops a chronology of uplift based on correlation of erosional surfaces in a peneplanation model. This peneplanation model builds on the work of King (1967), in which backwearing is the dominant process of creating a surface, as opposed to downwearing. The authors acknowledged that initiation of new erosional cycles requires a new set of base levels; their model focuses on pulses of uplift as the cause of the new base level.

The paper presents topographic profiles perpendicular to the shore that correlate erosional landforms and silcretes. These surfaces may be preserved as planed areas without pedimentation or as dissected remnants on interfluves and isolated residuals. A key assumption is that the Great Escarpment originally formed at the continental margin, 200 km from its present location inland. The authors also draw on the offshore sediment record and the spatial pattern of river drainages to support the resulting chronology. This correlation results in three main surfaces: the African erosion surface, the Post-African I surface, and the Post-African II surface.

The African surface results from erosion beginning during the breakup of Gondwanaland to the Early Miocene. The authors acknowledge that a single landscape cycle may not have proceeded uninterrupted during this entire period; however, the great antiquity of multiple events results in a single unit observable in the record. This cycle resulted in deep weathering and kaolinisation of the underlying rocks and widespread formation of duricrusts. A 400 m bench containing remnants of Eocene marine rocks included within the Alexandria Formation is here interpreted as a submarine extension of the African surface. This cycle of erosion ends with a phase of uplift during the Miocene. Total uplift ranges from 150 to 300 m, with tilting to the west.

The Post-African I surface is associated with raised beaches in several locations. At Pato’s Kop, the Post-African I surface merges with a raised


(Chap. 4)

LG/ KLH


137




beach at 160 m. Farther to the west, this surface merges into a marine platform at 300 m. The coastal platform of the Southern Cape corresponds to marine sub-aerial planation during the Post-African I cycle. The authors speculate that the Great Escarpment retreated by no more than a few tens of kilometres during this phase of erosion. This cycle was terminated by uplift in the Pliocene. Uplift in the Ciskei-Swaziland axis varied from 600 to 900 m of uplift; 200 m in Oudshorn; and 100 m or less in the west coast

The Post-African II surface resulted from major dissection of the coastal hinterland, resulting in flights of alluvial terraces along major rivers.

Reddering Memorandum: Contribution of the African Surfaces to the South African Landscape

2012 The author states that the Partridge & Maud paper is now almost 25 years old and has its failings, but is basically sound. It was never meant to be the final word on the topic, but was at the time an excellent compilation of the existing knowledge. Without solid evidence to the contrary, Partridge & Maud’s work is robust.

The study goes on to detail the locations of the Africa Surface and other surfaces, as well as incision.

p. 12—

In spite of river incision indicating substantial crustal uplift in the western Coega and Kouga fault corridors subsequent to development of the mature landscape straths of the post-African I surface, there has been no reactivation of the Mesozoic faults of the area for a period as short as 2 Ma or as long as 8 Ma. It would appear that the uplift was/is epeirogenic/isostatic in nature, rather than tectonic. As a proviso, to the northeast (e.g., in the area of the Mzimvubu River), where incision levels are substantially higher, there is a higher incidence of earthquakes than along the southern coast of South Africa.

No

Uplift Mechanisms—Critiques of Partridge & Maud

Brown et al. Morphotectonic Evolution of the South Atlantic Margins of Africa and South America

2000 In the pediplanation model of King (1967), erosion surfaces originally graded to sea level are subsequently uplifted with new denudational cycles propagating inland by knickpoint retreat along rivers. Partridge & Maud (1987) improved upon this model by linking coastal deposits to erosional surfaces. Several axioms of these landscape models are not valid under current geomorphological theory: continents are subject to widespread episodic uplift; all slopes experience parallel retreat for long distances; river knickpoints retreat inland over long distances; and extensive low-relief surfaces can only be formed in relation to base level represented by sea level.

No Seismotectonic Setting (Chap. 4)

LG/ KLH

Erlanger Rock Uplift, Erosion, and Tectonic Uplift of South Africa Determined with Cosmogenic

26Al and

10Be

2010 Partridge & Maud (1987) cited various lines of evidence to corroborate the timing of uplift, including offshore sedimentation on river deltas (Dingle et al., 1983); landscape dissection by river incision; worldwide Cenozoic sedimentation rates derived from a deep-sea drilling project (Davies et al., 1977); and the remnants of a 400 m marine terrace found in the southeastern Cape and the Ciskei (McMillan, 1990).

The author disputes the assumption that erosional surfaces were once at or near sea level and cites a lack of geological evidence. She recognises that these surfaces may be quite old; however, their palaeo-elevations and the assumption of a uniform age remain questionable.

The author disputes the correlation of pulses of sediments in the offshore record to cycles of erosion and uplift that produced the Africa and Post-African surfaces based on the correlation performed by Summerfield

Yes Seismotectonic Setting (Chap. 4)

LG/ KLH


138




(1985). There is good agreement between the Miocene and Pliocene unconformities; however, the earlier Oligocene and Late Cretaceous/Early Palaeocene unconformities are poorly correlated.

Partridge (1998) recognised that a zone of uplift was also inferred from the convex profiles of major rivers in southeastern South Africa. Erlanger notes that the convexities of these profiles can be attributed to changes in geology and grain size of the basin, and to variations in stream power.

Partridge (1998) inferred rapid uplift, based on an age of 3.3 Ma for 400 m deposits of the Alexandria Formation taken from McMillan (1990); this age has been questioned on the basis of fossil assemblages. Further, Erlanger’s incision rate of ~17 m/Myr along the Sundays River suggests that these deposits could be 22–25 Ma, resulting in a lower estimate of uplift rates for the 400 m surface.

Erlanger et al. Rock uplift rates in South Africa from Isochron Burial Dating of Fluvial Terraces

2012 This study determined rock uplift in South Africa from the long-term incision rate of the Sundays River, and from an uplifted marine terrace near Durban. This study dated the terraces with cosmogenic

26Al and

10Be, using both

isochron and simple burial dating methods. We fi nd that the Sundays River has incised at 16.1 ± 1.3 m/Myr for the past ~4 Myr, and the marine terrace yields a rock uplift rate of 9.4 ± 2.2 m/Myr These results are inconsistent with rapid Neogene uplift.

Yes Seismotectonic Setting (Chap. 4)

MEMA

Gilchrist et al. Post-Gondwana Geomorphic Evolution of Southwestern Africa: Implications for the Controls on Landscape Development from Observations and Numerical Experiments

1994 The landscape evolution model of King (1953) involves formation of a low-relief pediplain that extended towards the coast and was formed at sea level. The first landscape cycle was initiated during the fragmentation of Gondwana, and each subsequent cycle represents cyclical uplift of the landscape since rifting. Gilchrist et al. (1994) cast doubt on this interpretation since planation surfaces are often defined by resistant layers, inconsistencies between the offshore sedimentary record and chronology of King have been noted, and significant denudation has occurred inland of the Great Escarpment.

The three landscape cycles proposed by Partridge & Maud (1987) build on the landscape evolution model based on that of King (1953). The Partridge & Maud model (1987) suggests an isostatic threshold of escarpment retreat as an important factor in initiating new landscape cycles but is a misinterpretation of the flexural response. More recent work suggests that scarp retreat occurs after the formation of the margin.


LG/ KLH

Gilchrist & Summerfield

Differential Denudation and Flexural Isostasy in Formation of Rifted-Margin Upwarps

1990 This study concludes that marginal upwarps form in relation to differential unloading due to the contrast in denudation rates of the rifted margins and hinterland. Using data from southern Africa this study shows up to 600 m of upwarp can be attributed to this process.

No Seismotectonic Setting (Chap. 4) MEMA


Denudation, Isostasy and Landscape Evolution

1991 The idea that episodic uplift occurs in response to long-term denudational unloading has become widely accepted in the geomorphological community but is based on a misunderstanding of how the lithosphere responds to applied loads at the temporal and spatial scales relevant to landscape evolution.

Current tectonic models for both intraplate and interplate settings cannot readily account for the kind of long-term episodic uplift envisioned by Partridge & Maud (1987). Recent models of magmatic underplating, thermal perturbations, or mechanical unloading linked to extension involve a single major event associated with continental rupture. Gilchrist & Summerfield (1991) suggest that the geomorphic and sedimentological evidence on which the identification of episodic surface uplift has been


MEMA/ KLH


139




based deserves more rigorous reappraisal.

Summerfield Plate Tectonics and Landscape Development on the African Continent

1985 Identifies three uncertainties in the landscape chronology developed by King (1962):

1. Denudational cycles are considered to be initiated at the coast by continental uplift and to extend along the drainage system by scarp retreat and peniplanation.

2. Uplift and denudation are held to have been essentially synchronous over the continent, although the probability of considerable local difference in timing is observed.

3. Emphasis is placed on the flexure of the continental margin.

Notes that the four major unconformities identified in the offshore record by Dingle (1982) have a poor correspondence with the chronology of uplift and planation of King (1962). The unconformities identified by Siesser & Dingle (1981) may be complicated by the interrelationship of denudational and tectonic effects with sea level. Changes in gradient across the shelf may affect expression of sea level on the sedimentary record.


MEMA/ KLH

Uplift Mechanisms—Flexural Isostatic Rebound

Brown et al. Morphotectonic Evolution of the South Atlantic Margins of Africa and South America

2000 The greater depths of denudation along the coast compared with the continental interior imply a flexural isostatic response that would tend to maintain an upwarped topography parallel to the margin.


LG/KLH

Erlanger Rock Uplift, Erosion, and Tectonic Uplift of South Africa Determined with Cosmogenic

26Al and

10Be

2010 Performed isostatic modelling based on uplift rates inferred from burial ages and erosion rates presented in the study.

Characterised physiographic regions with a given erosion rate, as follows:

• 6 m/Myr for the Cape Fold Belt

• 14 m/Myr for the Coastal Plain

• 80 m/Myr for the Great Escarpment

• 30 m/Myr for the Lesotho Highlands

• 5 m/Myr for the Interior Plateau

Modelling was performed along three transects at the Sundays River and Durban with alternative effective elastic thickness of 60 and 80 km. The flexural isostatic rebound at the Sundays River is 9 m/Myr, regardless of the effective elastic thickness. At Durban, isostatic rebound is 8 m/Myr when effective elastic thickness is 60 km, and 9 m/Myr for 80 km.

Assuming that the long-term incision rate of 16.9 ± 1.2 m/Myr is a proxy for rock uplift rate, then the Sundays River experiences 8 ± 5 m/Myr of dynamic topography. The marine terrace at Durban yielded a rock uplift rate of 10 ± 3 Ma when corrected for Pliocene eustatic sea level. This yields rock uplift rates of 2 ± 5 m/Myr (60 km elastic thickness) and 1 ± 5 m/Myr (80 km effective elastic thickness) attributable to dynamic topography.

These results are consistent with the magnitude of surface uplift (6 m/Myr) predicted by Gurnis et al. (2000) or potentially a decrease in dynamic topography and surface elevation through time (Moucha et al., 2008), but are incompatible with rapid Pliocene uplift (Partridge, 1998).

Yes Seismotectonic Setting (Chap. 4) LG/KLH


Denudation, Isostasy, and Landscape Evolution

1991 The idea that episodic uplift occurs in response to long-term denudational unloading has become widely accepted in the geomorphological community but is based on a misunderstanding of how the lithosphere responds to applied loads at the temporal and spatial scales relevant to landscape


Flexural response of the lithosphere to post-rifting denudation has resulted in a marginal upwarp for

LG/KLH


140




evolution.

Recent work has expanded on the seminal review by Gunn (1949) and has led to the development of two distinct flexural models describing deformation of the lithosphere during loading (with denudation represented as a negative load).

The elastic model assumes that the lithosphere can be represented by an elastic lithospheric plate overlying an inviscid asthenosphere, where the response to a single loading event is instantaneous and therefore does not exhibit time-dependent behaviour.

The Maxwell viscoelastic model assumes that the lithosphere behaves elastically at short time scales but deforms as a viscous fluid over long periods of time (10,000–100,000 years).

The authors note that the elastic model of flexural isostasy is adequate for predicting the response of the lithosphere to changes in load from long-term denudation that occur over much longer time spans in excess of 100,000 years.

The authors provide a formulation for the elastic model and note that varying the elastic thickness of the lithosphere changes the isostatic response to a loading event.

The authors show that isostatic compensation is only episodic on the time scale of small, individual crustal displacements along faults in response to progressive loading, and exhibits lags in response to applied loads only on the time scale of sublithospheric mantle flow (10,000–100,000 years). Over the time scale of landscape evolution, isostatic compensation occurs continuously, but in a manner dependent on the relationship between flexural rigidity and the wavelength of the applied loads.

The continuous flexure of passive margins in response to progressive denudational unloading during their post-rifting evolution has produced a short-wavelength denudational load sufficient to generate a significant marginal upwarp with an amplitude of several hundred metres. Flexural isostasy appears to be the only mechanism capable of sustaining the marginal upwarp. The upwarp is thought to develop progressively from the time of continental margin formation and to not attain its maximum amplitude for 100 Ma after rifting.

southwestern Africa of several hundred metres 100 Ma after rifting.

Gilchrist et al. Post-Gondwana Geomorphic Evolution of Southwestern Africa: Implications for the Controls on Landscape Development from Observations and Numerical Experiments

1994 Describes the Great Escarpment as the seaward boundary of a marginal topographic upwarp that is subparallel to the coastline and generally defines the marginal drainage divide.

Exterior and interior catchments display contrasting drainage patterns. Exterior catchments are drained by relatively short, parallel rivers oriented perpendicular to the coastline, whereas drainages of the continental interior have dendritic patterns and connect with exterior drainages when interior rivers breach the drainage divide.

Recent work suggests that scarp retreat occurs after the formation of the margin. Denudation is focussed on the rift flanks of passive margins, resulting in flexural isostatic uplift in response to differential erosion.

The authors performed four numerical experiments from large-scale (50 km wide and 150 km long) surface process models with formulations for erosional denudation and mass transport.

Model 1 tests the effect of an erosionally resistant layer buried in a more erodible lithology. The model predicts that the edge of the resistant layer is bent upwards by the flexural response and becomes a drainage divide soon

No Seismotectonic Setting (Chap. 4) LG/ KLH


141




after exposure.

Model 2 tests the transition from a relatively humid to more arid climate. The initial escarpment declines rapidly and the exterior catchment widens under the humid conditions. Denudation rates decrease and slopes steepen at the divides under the arid conditions.

Model 3 tests the initial condition of having a drainage divide 100 km inland of the base of the initial tectonic escarpment. In this model, the escarpment and upland areas are strongly incised by rivers with low overall denudation rates on the interfluves. The steep-sided valleys persist with time, resulting in locally higher interfluves than the initial topography. The remaining 70 Myr of model evolution is characterised by isostatic uplift and enhancement of the escarpment, with very slow rates of escarpment retreat into the exterior.

Model 4 tests the effect of base-level lowering at a constant rate of 15 m/Myr. During the first 25 Myr, the model evolution was similar to other models. The next 50 Myr result in rejuvenation of interior drainage basins and more rapid escarpment denudation, although the escarpment retreat rate slows in response to progressive steepening of drainages on the interior side.

These results reinforce the interpretation that erosionally resistant layers or caprocks slow denudation rates and hence inhibit escarpment retreat.

Kooi & Beaumont Escarpment Evolution on High-Elevation Rifted Margins: Insights Derived from a Surface Processes Model that Combines Diffusion, Advection, and Reaction

1994 Numerical experiments of surface process models of large scale (1–1,000 km) long term (1–100 Myr) demonstrate that the principal controls on the evolution of an initially steep model escarpment are pre-existing topography and drainage patterns, the time scale of fluvial entrainment, the flexural response of the lithosphere, and relative components of short- and long-range transport processes. The model predicts that erosional escarpments will be preserved in uniform lithologies only on margins with long denudation histories or where the escarpment is the top of a drainage divide. The formation of escarpments is favored by arid climates and bedrock terrains.

No LG

Summerfield Plate Tectonics and Landscape Development on the African Continent

1985 Models of continental rifting and passive-margin evolution predict an initial zone of thermal uplift along a nascent margin following continental rupture. This is subsequently replaced by a coastal uplift induced by flexure and rotation of the margin associated with post-rifting thermal subsidence, sediment loading offshore, and denudational unloading inland. The presence of a marginal upwarp promotes development of a dual system of drainage, one part supplying sediment to inland basins, the other eroding back into the seaward flank of the marginal upwarp and providing the offshore sediment record. Modern river drainages likely developed long after the formation of the continental margin through capture of larger interior networks by local breaching of the coastal upwarp. It is unlikely that continent-wide erosion surfaces formed under these drainage systems.


Tucker & Slingerland

Erosional Dynamics, Flexural Isostasy, and Long-Lived Escarpments: A Numerical Modeling Study

1994 Landscape evolution models exploring the effects of erosion processes and the coupling between denudation and flexural isostatic uplift predict the necessary conditions for long-term escarpment retreat, as follows:

• Headward propagation of bedrock channels through incision.

• Low rate of sediment production relative to sediment transport.

• High continental elevation.

• Any process that pins an escarpment near the drainage divide, such as flexural isostatic uplift.

No LG


142




Van der Beek et al. Modeling Postbreakup Landscape Development and Denudational History Across the Southeast African (Drakensberg Escarpment) Margin

2002 Performed numerical surface process models of landscape development using escarpment retreat rates of ~100 m/Myr derived from AFT data for the Drakensberg (Brown, Summerfield, & Gleadow, 2002) as a boundary condition. Numerical modelling results suggest that this retreat rate is a consequence of the pre-breakup topography, with less contribution from the rheology of the lithosphere, lithological variations, and inland base level falls. These results indicate that the SE African margin has remained tectonically stable since breakup, with less than 25 km of total escarpment retreat.

No LG

Dynamic Topography—Mantle Processes

Adams & Nyblade Shear Wave Velocity Structure of the Southern African Upper Mantle with Implications for the Uplift of Southern Africa

2011 Uses broadband seismic data to image below the Kaapvaal Craton, and concludes that there is little evidence in the shear-wave-velocity structure of the mantle to indicate it is supported by an upper-mantle thermal anomaly. Alternative hypotheses for uplift are (1) heating from the tail of a Mesozoic plume and (2) buoyancy from the African Superplume.

No MEMA

Conrad & Gurnis Seismic Tomography, Surface Uplift, and the Breakup of Gondwanaland: Integrating Mantle Convection Backwards in Time

2003 Presents the results of a model (backwards integrated) of the history of mantle flow using a tomographic image of the mantle beneath southern Africa as an initial condition while reversing the direction of flow and analytically incorporating cooling plates as a boundary condition.

The model predicts that the large, seismically slow, and, presumably, hot structure beneath southern Africa produced 500–700 m of dynamic topography throughout the Cenozoic. Since ~30 Ma, uplift has moved from eastern to southern Africa, where uplift rates are ~10 m/Myr, consistent with observations.

During the Mesozoic, the modelled topographic high is situated near Gondwanaland rifting, raising the possibility that this buoyant structure may have been involved with this breakup.

The high topography of Africa stretches farther to the north and south than the model prediction: much of the higher topography in eastern Africa is probably not dynamic topography, but rather, related to volcanic activity and rifting that began in eastern Africa ~30 Ma.

No Tectonic Setting


• Zones of weakness, including both crustal and mantle (e.g., hot-spot tracks and lithospheric upwelling).

• Time history of mantle upwelling beneath southern Africa.

Fig. 4 a potential figure to use in presentation.

GIS_S0038_F4

KLH

Forte & Mitrovica Deep Mantle Flow High-Viscosity Flow and Thermochemical Structure Inferred from Seismic and Geodynamic Data

2001 Performed a viscous-flow model of the mantle and imposed a layer of high viscosity at 2,000 km depth. This layer affects mantle flow patterns and inhibits convective flow and deformation of the lower mantle. This high-viscosity layer likely results from lateral variation in iron content at depths greater than 2,000 km.

No MEMA

Forte et al. Joint Seismic-Geodynamic-Mineral Physical Modelling of African Geodynamics: A Reconciliation of Deep-Mantle Convection with Surface Geophysical Constraints

2010 This article uses new 3-D seismic tomography to create a convection model for Africa. The model shows mantle upwelling under volcanic centers and finds the ‘West African Superplume’ and ‘South African Superplume’ to be of similar scale and dynamic intensity.

No MEMA

Gurnis et al. Constraining Mantle Density Structure Using Geological Evidence of Surface Uplift Rates: The Case of the African Superplume

2000 Modelling predicted surface uplift rates required to produce 0.5–1 km of dynamic topography requires surface uplift on the order of 6 m/Myr to produce 1 km of dynamic topography centered beneath southern and eastern Africa.


Behaviour of the African Superplume

The African Superplume could not account for rapid uplift of Southern Africa as proposed by Partridge (1998).

MEMA/ KLH

Lithgow- Dynamic Topography, Plate Driving Forces and the African Superswell

1998 A low seismic, deep-mantle anomaly beneath southern Africa is attributed to a buoyant plume called the African Superplume. It is capable of

No Seismotectonic Setting (Chap. 4) MEMA/ KLH


143




Bertelloni &

Silver

producing vertical stresses from viscous flow driven by density contrasts in the mantle. These vertical stresses result in dynamically supported topography and visible surface deformation.

Moucha & Forte Changes in African Topography Driven by Mantle Convection

2011 This article uses modelling to infer southward propagation of a topographic swell. The swell formed in response to the African Superplume.

Fig. 2 (p. 709) shows the modelled change in dynamic topography every 5 Myr for the last 25 Myr.


Moucha et al. Dynamic Topography and Long-Term Sea-Level Variations: There is No Such Thing as a Stable Continental Platform

2008 Modelled time-dependent dynamic topography of the ocean basins over the past 30 Myr. Inferred that thermal subsidence was a result of dynamic topography offshore of western Africa as well as of downwelling mantle flow associated with plate subduction.

No MEMA

Nyblade &

Robinson

The African Superswell 1994 Notes that the series of oceanic swells in southeastern Atlantic Ocean were a continuation of the high plateau of southern Africa. These regions of high topography (the African Superswell) represent the surface expression of lithospheric heating below southern Africa.


Behaviour of the African Superplume

LG/ KLH

Pérez-Gussinyé

et al.

Effective Elastic Thickness of Africa and Its Relationship to Other Proxies for Lithospheric Structure and Surface Tectonics

2009 The effective elastic thickness (Te), of the lithosphere is a proxy for lithospheric strength. This paper presents a new Te map of the African lithosphere estimated from coherence analysis of topography and Bouguer anomaly data. The latter data set derives from the EGM 2008 model, the highest resolution gravity database over Africa, enabling a significant improvement in lateral resolution of Te.

The analysis finds that Te is high (~100 km) in the West African, Congo, Kalahari, and Tanzania cratons. Of these, the Kalahari exhibits the lowest Te. Based in part on published seismic and mineral physics constraints, it is suggested that this may reflect modification of Kalahari lithosphere by an anomalously hot asthenospheric mantle. Similarly, the Tanzania craton exhibits relatively lower Te east of Lake Victoria, where a centre of seismic radial anisotropy beneath the craton has been located and identified with a plume head, suggesting that low Te in this region also reflects modification of cratonic lithosphere by an underlying hot mantle. The lowest Te in Africa occurs in the Afar and Main Ethiopian rifts, where lithospheric extension is maximum. In the western Ethiopian Plateau, a local Te minimum coincides with published images of a low P and S seismic velocity anomaly extending to ~400 km depth. The Darfur, Tibesti, Hoggar, and Cameroon line volcanic provinces are characterised by low Te and no deep-seated seismic anomalies in the mantle. Corridors of relatively low Te connect these volcanic provinces to the local Te minima within the western Ethiopian Plateau. The low Te is interpreted to indicate thinner lithosphere within the corridors than in the surrounding cratons. These corridors may provide potential conduits for hot asthenospheric material to flow from the western Ethiopian Plateau to the volcanic provinces of central and western Africa.

No The effective elastic thickness, Te, is an alternative measure of lithospheric properties. The effective elastic thickness corresponds to the thickness of an idealised elastic beam that would bend similarly to the actual lithosphere under the same applied loads (Watts 2001).

Although Te does not represent an actual depth to the base of the mechanical lithosphere, its spatial variations reflect relative lateral variations in lithospheric mechanical thickness.

Africa has been practically stationary within the hot-spot reference frame during the last 30 Myr (Morgan, 1983), leading to long-lived interactions between hot upwellings in the mantle and the lithosphere (Burke 1996).

KLH

Simmons et al. Thermochemical Structure and Dynamics of the African Superplume

2007 Builds on the work of Forte & Mitrovica (2001) by combining seismic and geodynamic data sets into a 3-D model of thermal and chemical perturbations. The most significant chemical perturbation was found about 1,000 km above the core-mantle boundary. The combined model of thermal and chemical perturbations results in a plume with a reduced but still positively buoyant structure. The source of the chemical heterogeneities is denser material drawn into the buoyant plume from the base of the mantle, resulting in an eastward bend of the superplume at ~2,000 km depth. Reduction in buoyancy from previous models suggests substantially reduced dynamic support of southern Africa.

No Seismotectonic Setting (Chap. 4) MEMA /

KLH


144




Van der Hilst et

al.

Evidence for Deep Mantle Circulation from Global Tomography

1997 Uses seismic tomography to image the mantle and finds evidence for mantle-wide convective flow.

No MEMA

Uplift Mechanisms—Other Igneous Processes

De Wit The Kalahari Epeirogeny and Climate Change: Differentiating Cause and Effect from Core to Space

2007 Refers to Cretaceous uplift of Africa as the Kalahari epeirogeny. Refutes the idea of the African Superplume since the upper mantle beneath southern Africa is not anomalously warm, and discontinuities detected by seismic waves are found at typical depths. Proposed a temporal link between two episodes of exhumation during the Cretaceous and episodes of basaltic magmatism (132 and 90 Ma) and kimberlite intrusions (90 and 120 Ma). These events results in underplating beneath southern Africa as a result of far-field subduction processes associated with the African and Eurasian plate boundaries and/or lithospheric decoupling of the Falkland Plateau from southern Africa.


Flowers &

Schoene

(U-Th)/He Thermochronometry Constraints on Unroofing of the Eastern Kaapvaal Craton and Significance for Uplift of the Southern African Plateau

2010 Uses (U-Th)/He thermochronology to examine unroofing across the southern African Plateau. Most rocks cluster at 100 Ma. Significant Mesozoic unroofing is associated with large igneous province activity.


Torsvik et al. Plate Tectonics and Net Lithosphere Rotation over the Past 150 My

2010 This study developed a model of plate motion for the last 150 Myr and net lithospheric rotation for the last 30 Myr. Motion is dominated by movement of the Pacific Plate.

Table 1 lists the absolute motions of the African and Pacific Plates for the last 150 Myr.

No MEMA

The Great Escarpment and Uplift

Burke The African Plate 1996 Attributes much of the topography of the African Plate to mantle convection. Interprets a quiescent period from 65 to 30 Ma, and then ‘simultaneous outbreak’ of volcanism at ~30 Ma. Volcanism is attributed to mantle plumes.

Areas of active volcanism and rift-reactivated faults are normal faults because buoyancy related to plumes and to rift-related elevation has locally modified the general stress distribution.


De Wit Post-Gondwana Drainage Development of Diamond Placers in Western South Africa

1999 Based on fluvial deposits, this study infers Late Cretaceous erosion following the breakup of Gondwana; accelerated uplift of the southern and eastern coasts (80–100 Ma) resulting in a northern shift of drainages and the formation of the Orange River network; and Late Cenozoic reworking of Tertiary fluvial deposits.

The Cretaceous was the period of highest diamond transport and inferred erosion.


De Wit &

Ransome

Regional Inversion Tectonics Along the Southern Margin of Gondwana

1992 This study relates inversion tectonics in southern Africa to first- and second-order tectonic processes, including fusion and fission of continents and collision/extension processes.


Dobson et al. Dating the Emergence of the African Superswell: A Window into Mantle Processes Using Combined (U-Th)/He and AFT Thermochronology

2010 The mantle anomaly below southern Africa provides a mechanism for uplift but does not constrain the timing of uplift. Based on geomorphic and stratigraphic studies, three alternative evolutionary models have been proposed in the literature, as follows:

1. The major phase of uplift occurred in the Late Cretaceous (Nyblade & Sleep 2003).



145




2. The major phase of uplift occurred at ~30 Ma (Burke & Gunnell 2008).

3. Approximately 900 m of the modern topography was rapidly uplifted in the Plio-Pleistocene (Partridge & Maud 1987).

Doucouré & de

Wit

Old Inherited Origin for the

Present Near-Bimodal Topography

of Africa

2003 Reconstructed the palaeotopography of the African continent using seismic tomography and geologic data. Post-Cretaceous topographic effects were calculated and removed from the topography, as were eustatic sea level and erosion. The resulting palaeotopographic reconstruction shows southern Africa at high elevations during the Cretaceous and argues for pre-Cenozoic uplift.


Matmon et al. Pattern and Tempo of Great

Escarpment Erosion

2002 This study looked at 24 escarpments on passive margins and determined that the location of the escarpments is fairly stable through time. Thermochronologic data and sedimentary sequences in ocean basins suggest that initial tectonically controlled rift escarpments undergo rapid and significant erosion only during the earliest stages of seafloor spreading.

No MEMA

Matmon et al. Desert Pavement-Coated

Surfaces in Extreme Deserts

Present the Longest-Lived

Landforms on Earth

2009 Presents evidence for the persistence of desert pavements as geomorphic features. It also summarises many previous studies that used cosmogenic isotopes to date surfaces and determine erosion rates.

No Seismotectonic Setting (Chap. 4) used to set southern African erosion rates in a global context

Moore &

Blenkinsop

Scarp Retreat Versus Pinned

Drainage Divide in the Formation

of the Drakensburg Escarpment,

Southern Africa

2006 This study asserts that escarpments are controlled primarily by scarp retreat and the presence of layers resistant to erosion (Karoo basalts) rather than by the presence of inland drainage divides (Brown, Summerfield, & Gleadow [2002] model).

No MEMA

Ollier & Marker The Great Escarpment of

Southern Africa

1985 Morphology of the Great Escarpment indicates the greatest uplift parallel to the Great Escarpment and the least uplift in the Kalahari Basin. Uplift was likely related to the breakup of Gondwana, and the same process likely initiated escarpment formation and retreat.

The horseshoe-shaped escarpment with the Kalahari Basin in the middle suggests uplift of the continental margins rather than uplift around a point (volcanism or heat flow–related uplift).


Partridge Of Diamonds, Dinosaurs and

Diastrophism: 150 Million Years of

Landscape Evolution in Southern

Africa

1998 The African Superswell could account for ~1 km of uplift in southern Africa. No LG

Westaway et al. Rheological Differences Between

Archaean and Younger Crust Can

Determine Rates of Quaternary

Vertical Motions Revealed by

Fluvial Geomorphology

2003 This study tests the hypothesis that in the absence of tectonic forcing, uplift can be generated in continental crust by forcing of flow in the weak lower-crustal layer by surface processes. The study tests the hypothesis by comparing uplift rates along rivers using river terraces in Archaean crust (no weak lower-crustal layer) and younger crust.

Comparison of the Vaal River (Archaean crust) and Sundays River terraces (Proterozoic/Palaeozoic) shows much higher uplift rates in the younger crust, supporting the hypothesis.


Denudation Rates


146




Bauer et al. Thermal and Exhumation History

of the Central Rwenzori

Mountains, Western Rift of the

East African Rift System, Uganda

2010 Apatite fission-track and (U-Th)/He thermochronologies indicate accelerated cooling in Permo-Triassic and Jurassic times, followed by a long period of constant, slow cooling, and then a renewed accelerated cooling in the Neogene.

During the last 10 Myr, differentiated erosion and surface uplift affected the Rwenzori Mountains, with more pronounced uplift along the western flank.

The final rock uplift of the Rwenzori Mountains that partly led to the formation of the recent topography must have been fast and in the near past (Pliocene to Pleistocene).

Erosion could not compensate for the latest rock uplift, resulting in Oligocene to Miocene (U-Th)/He ages.


Belton & Raab Cretaceous Reactivation and

Intensified Erosion in the Archean-

Proterozoic Limpopo Belt,

Demonstrated by Apatite Fission

Track Thermochronology

2010 Kilometre-scale exhumation occurred over extensive regions of the Limpopo Province as two discrete events during the Cretaceous, one around 130 Ma and the other around 90 Ma.

Between 1.3 and 2 km of crust eroded over the 40 Myr interval.

Evidence for Palaeogene cooling may be attributed to the processes of valley incision and modest scarp retreat.

River rejuvenation in the Miocene significantly altered South Africa’s major drainage systems.

No Seismotectonic Setting (Chap. 4) GIS_S0023_F2

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LG/ KLH

Bierman &

Caffee

Slow Rates of Rock Surface Erosion

and Sediment Production Across the

Namib Desert and Escarpment,

Southern Africa

2001 Cosmogenic 10

Be and 26

Al analyzed from samples of bedrock, stream sediment, and clasts of desert pavement provide evidence for tectonic stability. Average bedrock erosion rates inland and seawards of the escarpment are indistinguishable (3.2 ± 1.5 m/Myr and 3.6 ± 1.9 m/Myr, respectively).

Erosion rates based on stream sediments are higher than erosion rates based on bedrock, ranging from 5 to 16 m/Myr. This result indicates that the landscape is eroding faster than bedrock. Clasts of desert pavement have individual exposure ages up to 2.7 Ma.


Namibian landscape approaches steady state because the landscape erodes both slowly and uniformly across the landscape. These erosion rates appear to be steady in time when compared with denudation rates determined from apatite fission-track results.

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Bierman et al. 10-Be Shows That Namibian

Drainage Basins Are Slowly, Steadily,

and Uniformly Eroding

2007 This abstract states that 10

Be ages from Namibia show slow, uniform erosion.


MEMA

Brown,

Cockburn, et al.

Combining Low Temperature Apatite

Thermochronology and Cosmogenic

Isotope Analysis in Quantitative

Landscape Evolution Studies

2002 Combining apatite fission-track and (U-Th)/He thermochronology data with cosmogenic isotope analysis indicated that escarpments in Namibia and South Africa are formed by rapid post-breakup river incision seawards of a pre-existing drainage divide located just inland of the present escarpment. The escarpment becomes pinned at this divide with moderate to low retreat rates (≤10 to 100 m/Myr).

No Meeting abstract contains no data. LG

Brown et al. Morphotectonic Evolution of the South

Atlantic Margins of Africa and South

America

2000 Apatite fission-track (AFT) analysis provides quantitative point estimates of the depth of rock removal over time and can therefore aid in understanding the morphotectonic history of continental margins. The technique is sensitive to temperatures less than 130° Celsius on time scales of 1–100 Ma.

AFT ages for the west coast of South Africa range from 166 ± 6 Ma to 70 ± 5 Ma, with ages predating breakup obtained from the interior regions of the continent.

AFT ages for Namibia range from 449 ± 20 Ma to 59 ± 3 Ma. Ages older than ~150 Ma are restricted to the Pan-African Damara metamorphic belt.

No The greater depths of denudation observed seawards of the escarpment compared with the continental interior imply a flexural isostatic response that would tend to maintain an upwarped topography parallel to the margin.

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The youngest ages of 70 Ma were obtained at Karasburg, where steeply dipping reverse faults associated with NW-trending shear zones and transverse faults form the western margin of the Kaapvaal craton. These data suggest an Early Cretaceous phase of enhanced denudation as well as a later, more variable phase of accelerated denudation associated with tectonic reactivation of regional crustal structure.

_P12.5b

Brown,

Summerfield, &

Gleadow

Denudational History Along a

Transect Across the Drakensberg

Escarpment of Southern Africa

Derived from Apatite Fission Track

Thermochronology

2002 Sampled a ~500 km long transect of apatite fission-track ages along the Drakensberg Escarpment from 15 boreholes. The coastal zone experienced a minimum of 4.5 km of denudation in the last 130 Myr. Borehole SW 1/67, located ~30 km seawards of the escarpment, indicates a total denudation of 3.1 ± 1.2 km since ~91 Ma, with an accelerated rate of erosion between ~91 and 68 Myr of 2.1 ± 0.9 km and a mean rate of 95 ± 43 m/Myr. Borehole LA 1/68, located west of the Lesotho highlands, indicates 1.7 ± 0.5 km of denudation since ~78 Ma, with accelerated denudation at 82 ± 43 m/Myr from 78–64 Ma

No Seismotectonic Setting (Chap. 4) GIS_D0021_F2

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LG/KLH

Burgess & Harris Cosmogenic Helium in Alluvial

Diamonds from Namaqualand, South

Africa

2005 The cosmogenic helium content for one diamond from Namaqualand is estimated at 73.5 x 10

–12 cm

3/g. Assuming a sea-level

3He production rate

at 30°S latitude, then the cosmogenic helium content corresponds to 16 Ma of surface exposure. This exposure is likely to have occurred since the late Tertiary, when diamonds were no longer being released from primary sources and were reworked from older terrace deposits.

No LG

Butler et al. Quantifying Denudation Rates in

Large Catchments from Cosmogenic

Nuclide Inventories: The Orange

River Basin, South Africa

2004 This abstract contains no data. No Meeting abstract contains no data. LG

Cockburn et al. Quantifying Denudation Rates on

Inselbergs in the Central Namib

Desert Using In Situ–Produced

Cosmogenic 10Be and 26Al

1999 Obtained denudation rates for six analyses from cosmogenic 10

Be and 26

Al from three granite inselbergs in the central Namib Desert, Namibia. Results range from 2.7 to 8 m/Myr and generally plot below the erosion island, implying complex exposure histories for these samples. Burial by dune sand is not a likely mechanism given the lack of geological evidence that the Namib Sand Sea has encroached on the sample area. Non-steady-state denudation may be caused by removal of spalling sheets ~1 m thick or by temporary shielding from toppled pedestal boulders.

These results are high when compared to inselberg denudation rates from Australia and may be due to salt weathering associated with fog precipitation in Namibia. These denudation rates correspond to 50 m of erosion over the past 10 Myr and probably more than 300 m during the Cenozoic. The denudation rates indicate that the majority of the 3–5 km of post-breakup denudation, as estimated by apatite fission-track dating (Brown et al., 2000), occurred by the end of the Cretaceous.


Mean summit lowering rate of 5.07 ± 1.1 m/Myr indicates slow rates of erosion in the last 10,000 years compared to estimates of denudation from apatite fission-track dating by Brown et al. (2000).

See data presented in Cockburn et al., 2000.

LG/ KLH

Cockburn et al. Quantifying Passive Margin

Denudation and Landscape

Development Using Combined

Fission-Track Thermochronology and

Cosmogenic Isotope Analysis

Approach

2000 Builds on the cosmogenic data set of Cockburn et al. (1999) and combines

this data set with apatite fission-track (AFT) thermochronology. A total of 20

granite-gneiss bedrock samples were collected along a transect from the

Atlantic Ocean to east of the Great Escarpment for AFT analysis. Thermal

histories modelled from AFT thermochronology indicate that between

breakup (130 Ma) and the end of the Eocene (36 Ma), mean denudation

rates for the coastal plain averaged ~40 m/Myr but fell to ~5 m/Myr up to


These data are consistent with a model of landscape evolution in which any initial escarpment formed near the coast at the time of breakup was degraded by river systems flowing from an inland drainage divide and adjusting to the new base level at the coast. The initial location of the escarpment may have originated only a few kilometres oceanwards of its present

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the present.

Inland of the escarpment, rates of denudation since breakup have remained

relatively constant at around 10 m/Myr. Cosmogenic 10

Be and 26

Al samples

collected along a transect at Gamsberg yield an escarpment retreat rate of

10 m/Myr and a summit downwearing rate of 0.4 m/Myr. The mean

denudation rate for coastal plain bornhardts is 5.1 ± 1.1 m/Myr. The

combination of the AFT and cosmogenic data supports the interpretation

that these rates have persisted since the late Cenozoic with a mean rate of

denudation across the coastal plain of ~5 m/Myr.

location, and its subsequent low rate of retreat has been controlled by pinning at the drainage divide, possibly enhanced by flexural isostatic rebound. These denudation rate data refute conventional escarpment retreat models of a major escarpment initiated along the coast at the time of breakup, requiring a mean escarpment retreat rate of >1 km/Myr.

Codilean et al. Single-Grain Cosmogenic 21Ne

Concentrations in Fluvial Sediments

Reveal Spatially Variable Erosion

Rates

2008 Assessed the variability in erosion rate of the Gaub River catchment by sampling sediment for

10Be, and fluvial pebbles for

21Ne. The frequency

distribution of these isotopes was then modelled in a DEM-based analysis to predict

21Ne concentrations in sediment leaving the catchment.

New sediment samples that drain the upland plateau have 10

Be rates of 7.9 ± 0.5 and 5.4 ± 0.3 m/Myr. Catchments below the escarpment have rates of 14.1 ± 0.9 and 12.5 ± 0.8 m/Myr.

When the previous results of Bierman & Caffee (2001) were recalculated, 10

Be rates based on small-catchment sediment samples confirmed the strong relationship between erosion rates and mean catchment slope. Above the escarpment, the bedrock rate is 3.2 m/Myr, with 0.5 m/Myr at Gamsberg. Sediment rates above the escarpment average 5 m/Myr, increase to 16 m/Myr at the escarpment, and then fall to 8 m/Myr below the escarpment.

Similarly, bedrock rates at the escarpment are 10 m/Myr and 3.6 m/Myr below the escarpment.

Fluvial quartz pebbles collected at the outlet of the Gaub River have 21

Ne concentrations that span two orders of magnitude. These concentrations require erosion rates that are lower than those obtained using

10Be in the

amalgamated sediment samples. The range of published 10

Be rates for bedrock in the catchment is 0.5– 11.7 m/Myr. Comparison of these data with a DEM analysis confirms that the

21Ne distribution is a signature of

slope dependence and spatial variation in erosion rates. Therefore, the landscape is not in steady state, with steeper areas eroding more rapidly.


The Gaub River is not in topographic steady state, with erosion rates higher at the steeper portions of the river at the escarpment than upstream and downstream of the escarpment. Erosion rates of the Gaub River catchment are slope-dependent.

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Cox et al. Erosion Rates and Sediment Sources

in Madagascar Inferred from 10Be

Analysis of Lavaka, Slope, and River

Sediment

2009 Erosion rates for river sediment from the central highlands of Madagascar average ~12 m/Myr.

No LG

Decker et al. Soil Erosion Rates in South Africa

Compared with Cosmogenic 3He-

Based Rates of Soil Production

2011 Presents cosmogenic 3He maximum denudation rates of 22 Karoo dolerite

bedrock surfaces. The mean maximum denudation rate for the Karoo dolerite surfaces sampled in this study is 3.2 m/Myr, although the probable mean rate of dolerite weathering is 1.9 m/Myr when excluding three samples from sloped surfaces.


Dimas & Brown Evolution of the South African

Drakensberg High-Elevation Passive

2003 Apatite (U-Th)/He analysis of deep borehole (CB-1) inland of the escarpment indicates a cooling of ~50°C at 90 ± 10 Ma, implying denudation of ~2 km during the mid-Cretaceous.



149




Margin: New Insights from Low

Temperature Thermochronologic Data

from Deep Boreholes

Dobson et al. Dating the Emergence of the African

Superswell: A Window into Mantle

Processes Using Combined (U-

Th)/He and AFT Thermochronology

2010 Meeting abstract contains no data. No Seismotectonic Setting (Chap. 4) LG/ KLH

Erlanger Rock Uplift, Erosion, and Tectonic

Uplift of South Africa Determined with

Cosmogenic Aluminum-26 and

Beryllium-10

2011 Erlanger obtained cosmogenic burial dates for fluvial terraces of the Sundays River originally mapped by Hattingh (2001). The upper terraces are strath terraces with a veneer of gravels. Erlanger sampled gravels at depth and determined burial ages from cosmogenic

10Be and

26Al. The

lower terraces were composed of fine-grained sediment, which allowed determination of bulk erosion rates in addition to burial ages.

Sundays River Terraces

Unilow (UL) site on terrace T13 of Hattingh (2001) has an age of 0.23 ± 0.15 Ma and an erosion rate of 2.52 ± 0.2 m/Myr.

Unifrutti (UF) site on terrace T11 of Hattingh (2001) has an age of 0.37 ± 0.19 Ma and an erosion rate of 3.8 ± 0.4 m/Myr.

Jagvlak (JV) site on terrace T11 of Hattingh (2001) has an age of 0.256 ± 0.153 Ma and a palaeo-erosion rate of 18.44 ± 13.0 m/Myr.

Canal (CL) site on terrace T10 of Hattingh (2001) has an age of 0.654 ± 0.0596 Ma and a palaeo-erosion rate of 7.53 ± 3.0 m/Myr.

Hattingh (2001) mapped the Lookout terrace as T8 but did not map the Lower Lookout (LL) site, which is lower in elevation. Based on elevations of the terrace and bedrock, Erlanger assigned the LL terrace to T9 and the Lookout terrace above it to T8. Erlanger assigned the Borrow Pit (BRW)

site to T9. The age of the LL site is 1.14 ± 0.384 Ma, and the palaeo-

erosion rate is 3.31 ± 0.54 m/Myr. The age of the Borrow Pit is 1.36 ± 0.357 Ma, and the palaeo-erosion rate is 24.0 ± 6.1 m/Myr.

The Railroad Cut (RRC) site corresponds to terrace T8 of Hattingh (2001); it

has an age of 3.20 ± 0.486 Ma and a palaeo-erosion rate of 18.1 ± 6.8 m/Myr.

The Uitkyk (UK) site corresponds to terrace T7 of Hattingh (2001); it has an

age of 4.06 ± 0.624 Ma and a palaeo-erosion rate of 4.74 ± 2.1 m/Myr.

The Kirkwood (KCS) site is located on T5, the highest and oldest surface sampled in this study. A burial age could not be computed for this sample because scatter in the data was too great to successfully regress a line through the data. This sample is probably older than 5 Ma.

Plotting these results against terrace elevation above river height results in an incision rate of 16.9 m/Myr. The grand mean of palaeo-erosion rate for all terraces except Unifrutti and Unilow is 6.62 ± 1.1 m/Myr.

Marine Terrace at Durban

The outcrop of a marine terrace recently exposed by a construction project near the Greenwood Park Railway Station in Durban was correlated to the ‘70-m bench’ of Davies (1970). The elevation was measured by Erlanger at 65.1 m asl. Twelve sandstone clasts collected from a gravel layer that lies 4.3 m below the terrace tread yielded a burial age of 4.26 ± 0.68 Ma. Sea-


These results support a flexural model with isostatic rebound rates of 8–9 m/Myr.

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level reconstructions at this time place early to mid-Pliocene sea level at 20–30 m. Correcting for this eustatic sea-level results in a rock uplift rate of 10 ± 3 m/Myr. With no correction, the uplift rate is 16.9 ± 1.2 m/Myr.

River Sediments

Sampled sediment from six rivers: the Tugela, Umgeni, Umzimvubu, Kei, Orange, and Caledon. Erosion rates for the southeastern coastal plain seawards of the Drakensberg Escarpment range from 9.34 to 22.4 m/Myr (samples Kei, Tugela2, and Umgeni). The Umzimvubu and Tugela1 sampling points represent the transition from the low topography of the coastal erosion to the high topography of the Lesotho Highlands and have variable erosion rates, ranging from 11.6 to 37.3 m/Myr. The Orange River sampling point captures sediment eroding from the Lesotho Highlands and has an erosion rate of 33.9 m/Myr. The Caledon sampling point reflects erosion rates of the inner piedmont and has a rate of 20.2 m/Myr.

The piedmont to the Drakensberg Escarpment is eroding at variable rates (11.6 ± 0.38 m/Myr and 37.3 ± 0.96 m/Myr), and erosion rates from the Drakensberg Escarpment are at least two times faster (86 ± 0.60 m/Myr). The Lesotho Highlands above the Great Escarpment are eroding twice as fast (33.9 ± 0.82 m/Myr) as the coast.

Erlanger et al. Rock Uplift Rates in South Africa from

Isochron Burial Dating of Fluvial and

Marine Terraces

2012 This study determined rock uplift in South Africa from the long-term incision

rate of the Sundays River, near Port Elizabeth, and from an uplifted marine

terrace near Durban. The terraces were dated with cosmogenic 26

Al and

10Be, using both isochron and simple burial dating methods. The Sundays

River has incised at 16.1 ± 1.3 m/Myr for the past ~4 Myr, and the marine

terrace yields a rock uplift rate of 9.4 ± 2.2 m/Myr. These results are

inconsistent with rapid Neogene uplift.


MEMA

Fleming et al. Denudation Rates for the Southern

Drakensberg Escarpment, SE Africa,

Derived from In Situ–Produced

Cosmogenic 36Cl: Initial Results

1999 Inferred denudation rates of the Drakensberg Escarpment from

concentrations of cosmogenic 36

Cl in free-face and summit outcrops of

basalt. Summit denudation rates range from 1.4 to 10 m/Myr, with a mean

rate of 6 m/Myr. Denudation rates from free-face outcrops imply

escarpment back-weathering rates of 49 and 63 m/Myr, assuming

denudation occurs as spalling of fragments thinner than the attenuation

length of 36

Cl production. If escarpment retreat occurs as removal of blocks

larger than the attenuation length, back-weathering rates could be as high

as 83 and 95 m/Myr. Therefore, estimates of escarpment retreat range from

50 to 95 m/Myr.

Existing longer-term estimates of denudation based on volcanic features

range from 1 to 3 m/Myr for the top of the basalt pile (corresponding to 4–6

m/Myr for the sampling sites) to 3 m/Myr (corresponding to 6–8 m/Myr since

the mid-Cretaceous for the sampling sites).

Denudation rates presented in the paper provide evidence that unmodified


Mean summit denudation rates of 6 m/Myr and calculated escarpment retreat rates of 50–95 m/Myr over the last 10

4- to 10

6-year time span

prevent intact survival of Mesozoic erosion cycle surfaces.

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Gondwana erosion surface remnants cannot have survived. The mean rate

of Drakensberg Escarpment retreat of 70 m/Myr implies that total

escarpment retreat to less than 10 km has occurred since the breakup

along the SE margin 135 Ma. This is more than an order of magnitude less

than the mean rate of retreat that would be required for the escarpment to

have moved to its present position from an original location at or near the

present-day coastline.

The authors suggest that the present escarpment would have originally

grown vertically through differential denudation as a feature pinned at the

seaward flank of the drainage divide. Escarpment retreat is also favored

where an escarpment coincides with a drainage divide and where

continuous back-tilting of the escarpment zone, due to flexural isostatic

response to denudational unloading, maintains the escarpment summit as a

drainage divide.

Flowers & Schoene

(U-Th)/He Thermochronometry

Constraints of Unroofing of the

Eastern Kaapvaal Craton and

Significance for Uplift of the Southern

African Plateau

2010 (U-Th)/He thermochronology for the Barberton Greenstone Belt indicates less than ~850 m of Cenozoic unroofing with negligible erosion since the Cretaceous.


GIS_D0015_F2b

LG/ KLH

Hattingh Late Cenozoic Drainage Evolution in

the Algoa Basin with Special

Reference to the Sundays River

Valley

2001 Analyses the terraces along the Sundays River to determine uplift and erosion rates. There are 13 mapped fluvial terraces along the Sunday’s River. They are grouped in to late Miocene to late Pliocene higher terraces at elevations of 220 m to 40 m above the moden river and Pleistocene to Holocene terraces at elevations of 25 m to 3 m above the modern river.


Ivy-Ochs & Kober Surface exposure dating with

cosmogenic nuclides

2008 Summarises cosmogenic nuclide dating methods and associated errors. No MEMA

Kounov et al. Present Denudation Rates at

Selected Sections of the South

African Escarpment and the Elevated

Continental Interior Based on

Cosmogenic 3He and 21Ne

2007 Presents erosion rates based on stable 3He and

21Ne obtained from dolerite

and quartzite samples. Samples were collected from the escarpment at Vanrhynspass, from Hantam Mountain and Williston of the Western Cape, and from Beaufort West of the Southern Cape.

Samples from Vanrhynspass have estimated minimum exposure ages at the edge of the escarpment of between 0.30 and 0.65 Ma, with corresponding maximum denudation rates between 1 and 2 m/Myr.

Mean vertical denudation rates of dolerite samples range between ~1.5 and 3 m/Myr.

Denudation rates are lower at Vanrhynspass than at the Hantam Mountain and Beaufort West sites, suggesting a slower denudation rate of the Table Mountain Group than the dolerite.

The lowest rate was obtained inland at Willston, suggesting an influence of climatic conditions.


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Kounov et al. Denudation Along the Atlantic Passive

Margin: New Insights from Apatite

Fission-Track Analysis on the

Western Coast of South Africa

2009 Apatite fission-track ages range from 180 to 86 Ma.

Modelling of these data identifies two distinct cooling events:

1. Between 160 and 138 Ma: recorded only by the rocks above the escarpment in the Karoo area; tentatively linked to post-Karoo magmatism (c. 180 Ma) thermal relaxation.

2. Between 115 and 90 Ma: linked to a tectonically induced denudation episode responsible for the removal of up to 2.5 km of crust across the coastal zone in front of the escarpment and less than 1 km on the elevated interior plateau.

These results suggest that most of the elevated topography of Southern Africa was generated during the Cretaceous, with only a minor Cenozoic contribution.


LG/ KLH

Luft et al. Post-Gondwana Break-Up

Constraints from Apatite Fission Track

Thermochronology in NW Namibia

2005 Thermal modelling indicates accelerated uplift and/or upwarping of the local crust at 130 Ma, followed by a gradual and continuous cooling history.


Luft et al. Tectono-Thermal History of the Kaoko

Belt, Namibia: An Integrated Low

Temperature Thermochronology

Study

2006 (U-Th)/He ages for the Kaoko Belt of Namibia provide evidence for accelerated denudation in the Cretaceous, based on apatite fission-track ages of ~70 Ma.


Portenga & Bierman

Understanding Earth’s Eroding

Surface with 10Be

2011 This paper presents a global compilation of 10

Be analyses. This data set includes only the Cockburn et al. (2000), Bierman & Caffee (2001), and Cox et al. (2009) work. Results confirm that outcrop erosion rates are more than 15 times slower than those inferred from drainage basin studies.


Raab et al. Denudational and Thermal History of

the Early Cretaceous Brandberg and

Okenyenya Igneous Complexes on

Namibia’s Atlantic Passive Margin

2005 Apatite fission-track transects along Brandberg and Okenyenya inselbergs provide evidence for rapid exhumation between 80 and 60 Ma (0.2–0.125 km/Myr) and 5 km of denudation since the Late Cretaceous, with denudation rates of 0.023–0.15 km/Myr in the early Tertiary.


LG/ KLH

Scharf et al. Denudation Rates and Geomorophic

Evolution of the Cape Fold Belt,

Determined Through the Use of In

Situ–Produced Cosmogenic 10Be

2011 This abstract and poster present the results of a study to quantify denudation rates along the western limb of the Cape Fold Belt (CFB) through the analysis of in situ–produced cosmogenic

10Be in quartz from

river sediment and bedrock samples. 10

Be denudation rates for the CFB are between 2.3 ± 0.4 m/Myr and 7.2 ± 2.0 m/Myr, suggesting that the present-day landscape is not likely the result of neotectonic uplift in the region. (Abstract)

Within the Langeberg and Swartberg ranges of the CFB, Western Cape, sediment samples were collected from 10 rivers, while bedrock samples were collected from two modern fluvial benches and four outcrops along interfluvial slopes. Pebbles were collected from two depositional terraces, for a total of seven samples removed from the profiles. Samples collected from flats on interfluvial slopes have elevations of 392 m, 429 m, and 489 m. Samples collected from modern river benches along the Tradow River have elevations of 226 m and 232 m. 10

Be-based denudation rates of the CFB fall between 2.3 ± 0.4 m/Myr and 8.8 ± 0.2 m/Myr. The similarity between catchment-averaged denudation rates (determined from river sediment samples) and denudation rates on interfluves (determined from bedrock samples) indicates a topography in

Yes Denudation Rates for Kango Fault (8.4.1)

10Be denudation rates for the western Cape

Fold Belt fall between 2.3 ± 0.4 m/Myr and

8.8 ± 0.2 m/Myr.

Seismogenic Probability of the Worcester

Fault (8.4.5)

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153




approximate steady state, neither increasing nor decreasing in relief. These results indicate very low erosion rates within deeply incised canyons, suggesting that the present-day landscape of the CFB is not likely the result of neotectonic uplift in the region. (poster)

Scharf et al. Strong Rocks Sustain Ancient

Postorogenic Topography in Southern

Africa

2013 Uses 10

Be erosion rates to determine the cause of steep topography in the Cape Mountains of South Africa, as well as to determine the region’s tectonic stability in the Cenozoic. 10

Be-based catchment-averaged denudation rates vary between 2.32 ± 0.29 m/Myr and 7.95 ± 0.90 m/Myr. We attribute the maintenance of rugged topography and suppression of denudation rates primarily to the presence of physically robust and chemically inert quartzites that constitute the backbone of the mountains.

10Be-based bedrock denudation rates on the

interfluves of the mountains vary between 1.98 ± 0.23 m/Myr and 4.61 ± 0.53 m/Myr.

Yes Denudation Rates for Kango Fault (8.4.1)

Seismogenic Probability of the Worcester

Fault (8.4.5)


KLH

Summerfield et al. Problems in Deriving Surface Uplift

Histories from Geomorphic Data: The

Case of South-East Africa

2000 The use of apatite fission-track thermochronology and cosmogenic isotope analysis can reconstruct regional denudation histories and evaluate landscape evolution models.

No Meeting abstract contains no data. LG

Tinker et al. Linking Source and Sink: Evaluating

the Balance Between Onshore

Erosion and Offshore Sediment

Accumulation Since Gondwana

Break-Up, South Africa

2008a Using 173 wells and a seismic reflection profile, calculated the volume of sediment accumulated in the Outeniqua and Southern Outeniqua Basins since ~136 Ma: 268,500 km

3.

Accumulation volumes and rates were highest in the Early Cretaceous and Middle to Late Cretaceous. Volumes and accumulation rates were lowest for the Early to Middle Cretaceous and the Cenozoic.

The accumulated volume of offshore sediments does not match the calculated volume of onshore erosion, as quantified through apatite fission-track thermochronology.

The timing of increased sediment accumulation closely matches the timing of increased onshore denudation.

The greatest volumes of material were transported from source to sink during two distinct Cretaceous episodes.

The processes driving onshore denudation decreased by an order of magnitude during the Cenozoic.


Tinker et al. Mesozoic Exhumation of the Southern

Cape, South Africa, Quantified Using

Apatite Fission Track

Thermochronology

2008b Quantifies the timing and extent of exhumation across the Southern Cape escarpment from outcrop and borehole samples.

The 25 outcrop samples follow the same north-south route as regional seismic reflection and refraction profiles, crossing the late Neoproterozoic Kango inlier, the Cape Fold Belt, the Jurassic-Cretaceous Oudtshoorn Basin, the Great Escarpment, and the Karoo Basin and ending near the edge of the Archaean craton. Apatite fission-track ages for outcrop samples indicate that significant cooling occurred in the Cretaceous with major cooling over by ~65 Ma.

These ages are consistent with denudation postdating thermal Cape Orogeny. Uplift ages for all outcrop samples are younger than the Cape Orogeny (~250 Ma) and only a few ages are older than the Karoo igneous event (183 Ma), indicating that emplacement of the Karoo basalts reset apatite grains in the region.

A set of 31 samples was collected from three deep boreholes that form an east-west profile on the seaward side of the escarpment within the Karoo


GIS_D0016_F1

LG/ KLH


154




Basin.

The data indicate that 2.5–3.5 km of denudation occurred during the mid-Late Cretaceous at a rate of 175–125 m/Myr. Less than 1 km of denudation has occurred since the Late Cretaceous.

Van der Wateren & Dunai

Late Neogene Passive Margin

Denudation History—Cosmogenic

Isotope Measurements from the

Central Namib Desert

2001 Sampled cosmogenic 21

Ne from pediment surfaces, inselbergs, and sediment from Namibia. 21

Ne ages from quartz veins at the Hope Mine sites show a steady

younging trend from SW to NE with increasing elevation. The central Namib

pediment has a minimum age of 5.18 ± 0.18 and 3.97 ± 0.25 Ma.

Alternatively, these samples provide denudation rates of 0.11 and 0.15

m/Myr.

Quartz veins are the most resistant landforms on the plains, and the oldest

veins project 5–10 m above the regional pediment, implying 5–10 m of total

surface lowering. Assuming this has occurred in the last 10–15 Ma, the

regional rate of surface lowering is on the order of 0.3–1 m/Myr.

Pebble samples from Carp Cliff and Kamberg Cliff provide an age of

abandonment of the highest river terrace of 2.81 ± 0.11 Ma.

Major late Neogene incision occurred ~2.8 Ma in the central Namib west of

the escarpment, slowing down or stopping in the early to mid-Pleistocene

~1.3 Ma at a distance of ~100 km from the river mouth and ~0.4 Ma at 200

km from the coast. The Kuiseb River has an incision rate of 40–160 m/Myr

during the early to mid-Pleistocene.

Incision was preceded by (1) aggradation of aeolian sands, fluvially

reworked sands, and fluvially deposited boulders and gravels; (2) a period

of widespread formation of calcrete in the terrace sediments; and (3)

stream redirection.

Denudation rates in the Kuiseb headwaters were very slow during the

period prior to conglomerate deposition (0.3–0.7 m/Myr) and are the same

order of magnitude as the long-term denudation rate, based on pediment

samples and the summit of Gamsberg (Cockburn et al., 2000).

Downcutting of the Kuiseb and Swakop Rivers occurred synchronously in

both basins, and development of calcretes at this time reflects regional

climatic influences.


Steady-state denudation rates of inselbergs

(Cockburn et al., 2000) derived from 10

Be and

26Al are an order of magnitude higher than those

on the Kuiseb and Gaub river-cut surfaces.

Drainage around the Mirabib inselberg was most

likely influenced by base-level lowering following

incision of the Kuiseb Canyon after ~2.8 Ma.

Central Namib inselbergs were excavated

relatively recently or experienced accelerated

denudation as a result of regional river

downcutting and erosion of thick sediment cover,

consistent with complex burial history observed in

Cockburn et al.’s (2000) work. Inselbergs may

have been excavated recently from a deep

weathering regolith in response to local base-

level lowering due to river incision.

Denudation rates from pediment surfaces (≤1

m/Myr) are representative of the late Neogene

landscape evolution of the central Namib since

the onset of the Benguela upwelling system.

Following the initial phase of substantial

post-breakup denudation, the passive margin

is characterised by long-term slow

denudation punctuated by periods of

accelerated denudation starting 2.8 Ma and

ending between 1.3 and 0.4 Ma. Areas

representative of long-term denudation have

to be looked for on interfluves as far away as

possible from areas undergoing local rapid

surface drawdown.

LG/ KLH

Willet et al. Tectonics, Climate and Landscape 2006 This introduction summarises interactions between tectonics, surface erosion processes, and climate.



155




Evolution



156

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173

Table 3.6. Data Summary Table - Quaternary, Thyspunt PSHA.


Are the

Data Used

in the SSC


Sedimentation Rates

Rau et al. Late Quaternary Paleoceanographic

Record in Giant Piston Cores off

South Africa, Possibly Including

Evidence of Neotectonism

2006 p. 76—

Comparative study of late Quaternary deep-sea sediments in three giant

piston cores from the Olifants River slope (ORS), the Agulhas Bank slope

(ABS), and the Natal Valley (NV) shows that sediments of hypothermal

(glacial) periods are characterised by assemblages of planktonic

foraminifera Neogloboquadrina pachyderma, which are accompanied in

core ABS by higher amounts of glauconite and very fine quartz sand,

probably swept seawards by storms when the outer shelf was shallower

during lowstands. Tropical planktonic foraminifera is found in trace

amounts, even in sediments of hypothermal periods, showing that at the

latitude of the core ABS (36°16′S), warm Agulhas Current water was not

completely choked off by any equatorward shift of the Subtropical

Convergence.

p. 67—

Mean sedimentation rates inferred from oxygen isotope data are as

follows:

ORS—3.6 m/kyr (MIS 21.3, 838 ka, at depth of 30 m)

ABS—1.9 m/kyr (MIS 20.2, almost 810 ka, at depth of 15 m)

NV—3.8 m/kyr (MIS 16, 630 ka, at depth of 24 m)

p. 73—

The interval between MIS 11 and 7 (425–185 ka) records a change in

surface-water dynamics. May correspond to “Mid-Brunhes climatic event”

observed elsewhere in the Southern Hemisphere (Jansen et al., 1986).

Within core ABS there is evidence for a transition from more limited

variability on glacial-interglacial time scales during the interval between

MIS 11 and 7 to overall warmer conditions, as well as the development of

a glacial-interglacial cyclicity for the period between MIS 7 and 1.

p. 75—

Three major turbidites of quartz sand characterise the Natal Valley core;

they have ages of 510 ka (MIS 13); 335–340 ka (MIS 10); and 250 ka

(MIS 8) (pp. 65 and 75). Two additional minor turbidites (485 ka, MIS 13;

455 ka, MIS 12) also are recognised. If these turbidites were triggered by

major earthquakes, it suggests an average recurrence interval of 65 kyr.

The lack of events in the past 250 kyr suggests that either earthquake

No Indirectly, sedimentation rates have implications

regarding erosion in both onshore and offshore

regions.

Onshore erosion/offshore deposition rates are a

factor to consider in evaluating differential

uplift/subsidence resulting from isostatic

adjustments.

Limited sediment accumulation may indicate

erosion in offshore environments that could

explain offshore scarps.

Tsunami hazard recurrence

Timing of turbidite deposits in Natal Valley.

KLH


174


Are the

Data Used

in the SSC


activity has subsided in the past 250 kyr or a high-magnitude earthquake

may be overdue.

Coastal Dunes

Bateman et al. Aeolianite and Barrier Dune

Construction Spanning the Last Two

Glacial-Interglacial Cycles from the

Southern Cape Coast, South Africa

2004 Provides a regional chronology for the coastal aeolianites of the southern

Cape that spans at least the last two glacial-interglacial cycles. Aeolianite

deposition has occurred on the southern Cape coast ca. 67–80, 88–90,

104–128, 160–189, and >200 kyr BP. The authors conclude that these

depositional phases appear to be controlled by interglacial and

subsequent interstadial sea-level highstands. The lack of carbonates in

more recent dunes (MIS 1/2 and 4/5) is attributed not to leaching but to

changes to carbonate production in the sediment source area caused by

increased terrigenous material and/or changes in the balance between

the warm Agulhas and nutrient-rich Benguela ocean currents.

The majority of the sedimentary record examined probably relates not to

deposition during interglacial highstands but to post-interglacial periods

(interstadials) when sea levels were fluctuating and climatic conditions

were cooler and wetter—and therefore more conducive to

cementation/preservation.

Wilderness cordon dunes—The gross stratigraphy of the site comprises

the fossil dune core, a weathered horizon, overlying sand, and a modern

soil horizon.

Agulhas ridge (cordon dune)—2.7 m exposure upper is variably

cemented, carbonate-rich sand; lower is less cemented sand.

Soetendals Valley (cordon dune)—Variably cemented sands; upper 1–

0.5 m is bioturbated.

Hoe Walle (aeolian sand, possibly not dune)—Upper well-indurated

calcrete pedogenic caprock. Lower sands less cemented. Overlies the

silty clays of the Klein Brak Formation.

The single-grain data for sample Shfd02007 (Wilderness cordon) show a

tail of high palaeodoses similar to those obtained from the underlying

basal aeolianite, perhaps indicating that some sediment from the lower

unit was locally recycled, without full bleaching, during the deposition of

the lower friable sand unit. This would support the hypothesis of episodic

deposition of the lower aeolianite unit. The individual beds within the

aeolianite, both cemented and uncemented, could be interpreted as the

product of episodic deposition followed by deflation, erosion, and

No Regional chronostratigraphic framework to

evaluate dunes at Thyspunt.

KLH


175


Are the

Data Used

in the SSC


reworking of sand.

Two conditions are necessary to build dune cordons: large-scale

entrainment and deposition of calcareous sand and sub-aerial

cementation of the sand.

In contrast to previous highstands, the highstand of the present

interglacial has not seen aeolianite deposition, but rather the building of

unconsolidated sand dunes.

First, it is clear that a significant amount of aeolian deposition occurred

after the high sea stand associated with the Eemian. Second, dunes and

aeolian sediments appear to have been deposited when sea levels were

rapidly changing. The aeolian sedimentation during periods postdating

interglacials also explains why many of the aeolianites and cordon dunes

found on the present-day coastline are being eroded, as sea levels would

have been marginally lower than the present day while they were being

deposited.

Bateman et al. The Evolution of Coastal Barrier

Systems: A Case Study of the

Middle-Late Pleistocene Wilderness

Barriers, South Africa

2011 Abstract—

Tectonic stability at Wilderness allowed glacio-eustatically formed

shorelines to occupy similar positions on multiple occasions. This, in

conjunction with a relatively humid climate and a well-vegetated

landscape, enabled deflated sediment from beaches to form dunes that

stacked on one another to form an extensive and complex vertical

accretionary sequence.

p. 69—

Elongate topographic low on the continental shelf trending approx. SE–

NW in the centre of the embayment interpreted as lowstand palaeo-

estuaries of the Touws and Swart Rivers.

Volumetrically, the MIS 1 sedimentation phase up to the present time is

less than that for either of the older landward or middle barriers. This may

reflect the longer duration of MIS 7 and 5 and the physical impediment of

the pre-existing large barriers. The lower volume of MIS 1 sediment

contrasts with models put forward for barrier development by Cooper et

al. (2002) and Armitage et al. (2006) in Mozambique, and Porat & Botha

(2008) in KwaZulu-Natal.

Marine platforms eroded into aeolianite dating to the MIS 6/MIS 5e

transition are mantled in places by marine facies clearly postdating the

MIS 5 aeolian sedimentation on the middle barrier, suggesting more than

No Evolution of coastal barrier dunes with

Pleistocene sea-level variation.

Indirectly provides evidence for tectonic stability

of the south coast of the East Cape region.

MEMA


176


Are the

Data Used

in the SSC


one highstand during MIS 5 as noted by Carr, Bateman, et al. (2010).

This is supported by Hearty et al. (2007), who produced a high-resolution

summary MIS 5 sea-level curve based on far-field geomorphic features,

in which MIS 5e sea levels rapidly rose to 2–3 m amsl before 130 ka, fell

to 0 m amsl around 125 ka, and then rose to sea levels of 6 to 9 m amsl

ca. 120 ka. Notwithstanding the uncertainties associated with the OSL

dates, the data clearly suggest that by 120 ka, at least part of the

seaward barrier was in place and lithified.

Butzer & Helgren Late Cenozoic Evolution of the Cape

Coast Between Knysna and Cape

St. Francis, South Africa

1972 This article examines Cenozoic erosional end depositional records

between Knysna and Cape St Francis. The 200 m planation surface is

associated with fanglomerates and deltaic sediments of the Keurbooms

Formation. Erosion up to 120 m was followed by land rubble and littoral

deposits of the Formosa Formation to 101 m. Other sea levels are at 60,

30, and 15–20 m. Beaches at 5–12 m with thermophile mollusca that

date to >40 ka mark the Swartskops horizon and are probably from the

Eem Interglacial period. The Wurm interglacial is represented by

cryoclastic screes and cave deposits. Aeolian deposits after 16 ka were

interrupted by pedogenesis ca. 7,500 yr BP and stabilised after 4,200 yr

BP when sea level reached +2.5 m. There has been human-induced

activation of the dunes since the 18th century.

p. 163—

The region has evidence for frost weathering, although in the current

climate it rarely freezes.

p. 164—

Three generations of Holocene alluvial fill and terraces can be found

upstream of Loerie along the Gamtoos drainage. Peat from the middle fill

had a C14 age of 4,010 ± 70 yr BP near the base and 1,330 ± 110 yr BP

near the top. By about 1,000 yr BP, geomorphic equilibrium was upset,

with dissection followed by rapid aggradation of coarse sands.

Yes Gamtoos Fault (8.4.3)

Information on possible Quaternary datums can

be used to correlate marine terraces and

evaluate evidence for Quaternary reactivation.

MEMA/ KLH

Carr et al. Climatic and Sea Level Controls on

Late Quaternary Eolian Activity on

the Agulhas Plain, South Africa

2006 This paper discusses episodic lunette dune deposition on the Agulhas

Plain 60–45, 13–12, 2.8–2.6, 1.2, and <1 ka; coastal dunes cluster 4.7–

4.1 ka.

Lunette orientation is indicative of strong westerly winds in Pleistocene

and Holocene time. Lunette accretion is promoted by reduced onshore

moisture transport during summer months, enhancing rainfall seasonality.

Such conditions likely were promoted by increased continentality as the

No Regional chronostratigraphic sequence

Most pertinent for Western Cape region.

KLH


177


Are the

Data Used

in the SSC


Algulhas Bank was exposed during sea-level lowstands.

Lunette dune accretion is asynchronous between locations.

Carr et al. Developing a 150 ka Luminescence

Chronology for the Barrier Dunes of

the Southern Cape, South Africa

2007 This paper presents results from a single 6.5 m section in the seaward

barrier dune near the town of Wilderness.

Peaks in aeolian activity date to 157–154 and 140–125 ka, with a slower

rate of deposition recorded 115–85 ka.

Brief phases at 40 and 21 ka also are identified. Some ages, notably from

oxygen isotope state (OIS) 3 and OIS 2 are surprising from a

geomorphologic perspective, given the likely distance of the dune from

the shoreline at such times, although they are not inconsistent with

evidence from the east coast of South Africa. These may be related to

reworking under more arid glacial conditions.


Regional chronostratigraphic framework to

evaluate dunes at Thyspunt.

Note: General observation of multiple phases of

aeolian activity before, during, and since the last

interglacial.

Results show that distinct phases of deposition

within apparently homogeneous sedimentary

units make it difficult to correlate and interpret

coastal sequences based purely on lithological

characteristics (e.g., Malan, 1990) (p. 115).

OSL dating—dose rate

Low dose rates consistently encountered in the

coastal sediments of this region (300–800

micrograys per year (µGya/yr), where a gray is

an SI unit of absorbed radiation (p. 115).

KLH

Chase & Thomas Multiphase Late Quaternary Aeolian

Sediment Accumulation in Western

South Africa: Timing and

Relationship to Palaeoclimatic

Changes Inferred from the Marine

Record

2007 Describes results of OSL dating of 35 samples from six dune cores along

a N-S transect extending from Elanda Bay (37°26′S, 18°14′E) to Kleinsee

(29°14′S, 16°59′E). Ages exhibit five distinct peaks, which suggest

phases of activity/deposition at 4–5, 16–24, 30–33, 43–49, and 63–73 ka.

Spatial and temporal extent allowed for correlations to marine core data

from southeast Atlantic. Results suggest that environmental changes in

this region cannot necessarily be equated with periods of increased

aridity, with other factors such as wind strength and sediment supply

being of critical importance (p. 29).


Results indicate that phases of activity since the

last interglacial (MIS 5) on the western coastline

of South Africa may be tied to a variety of

factors (e.g., wind strength and sediment

supply—not just aridity).

GIS_S0032

_F2

Figure 2

provides

good

compilation

of aeolian

dates for

West Coast

KLH

Compton &

Franceschini

Holocene Geoarchaeology of the

Sixteen Mile Beach Barrier Dunes in

the Western Cape, South Africa

2005 This study dated bulk dune sand, gull and human transported shells from

the dunes in Yzerfontein and Saldanha Bay. The authors concluded that

the dunes had prograded episodically seawards and that there is

evidence for a fall in sea level at 5,900, 4,500, and 2,400 yr BP.

No MEMA

Dunajko Mid- to Late Quaternary Evolution of

the Wilderness Barrier Dunes, South

Africa

2011 p. 151—

Particle-size analysis indicates that beach, lagoon, or cover sands could

have been a source for the barrier dunes. The river could have been a

source as well, through aeolian selection of only sand-sized grains.

p. 152—

No Ages of dune formation and coastal evolution MEMA


178


Are the

Data Used

in the SSC


Fines are likely due to postdepositional breakdown of larger grains.

p. 185—

The maturity of the Holocene dune sample relative to the other seaward

barrier samples supports the assertion that the Holocene dunes are

formed from recycling of seaward barrier aeolianites. The presence of the

authigenic marine mineral glauconite in the seaward barrier aeolianites

confirms that they contain a marine component.

p. 186—

Differences in particle-size distributions among the three barriers are

negligible, indicating no significant changes in transport regime or

sediment source between them.

Parabolic dunes, such as those that have coalesced to form the majority

of the Wilderness barriers, are migratory in nature. OSL dating of such

features records the cessation, rather than initiation, of aeolian activity

(Chase & Thomas, 2006). Figures 7.2 and 7.4 provide a good

visualisation of dune ages and sea level.

p. 193—

Base of middle barrier MIS 7, contemporaneous with some parts of the

landward barrier.

p. 194—

The majority of seaward barrier ages fall within MIS 5, in accordance with

Illenberger’s (1996) model. Aeolian activity ceased around 75 ka,

coincident with eustatic sea level falling below approx. –50 m amsl. Dune

accumulation resumed on the seaward barrier crest during the Holocene

as sea levels once again reached a highstand position. There is a lack of

evidence for barrier formation under low sea levels in the period between

MIS 2 and 4.

p. 203—

Dunes near steeper bathymetry have longer periods of activity (i.e., the

coastline was more stable during sea-level change).

p. 209—

The paucity of Holocene dune accumulation is interpreted as potentially

reflecting the lack of accommodation space left within the embayment.

p. 212—

Nearshore sediment accumulation around Wilderness is more abundant

than anywhere else on the southern African coast due to alongshore drift


179


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in the SSC


of Gouritz River sediments.

Illenberger The Geomorphologic Evolution of

the Wilderness Dune Cordons,

South Africa

1996 The term dune cordon describes large shore-parallel dune ridges built by

the accretions of a variety of dunes and dunefields. Dune cordons are up

to 200 m high and 3 km wide in the Wilderness area.

This paper describes three major dune cordons formed along the central

portion of the south coast of South Africa east of the town of George. The

dune cordons consist of steep-sided ridges up to 207 m high separated

by coastal lakes. There is an additional huge coalesced mass of older

fossil dunes landwards of these cordons, forming hills up to 340 m high,

in places lying on the coastal platform (150–260 m, generally; 210–260

m, locally). Dunes ~35% carbonate sand. Over time, the percentage of

carbonate is reduced.

Dune cordons can result from numerous phases of dune formation during

periods of sea-level highstand. The geomorphology is primarily a function

of dune-cordon construction accentuated by coastal erosion in the form

of cliff-cutting; secondarily, of dune morphology; and thirdly, of fluvial

erosion.

Ages are based on the assumption that cordons formed only during

Pleistocene interglacials. The seaward cordon formed during the Eem

and Holocene; the middle cordon probably formed between 200 and 500

ka, and the landward cordon probably formed between 600 and 900 ka.

No Indirectly

Regional chronosequence providing some

relative age information for coastal deposits in

the vicinity of the Gamtoos Fault.

GIS_S0031

F2

GIS_S0031

_F6

GIS_S0031

_F7

GIS_S0031

_F8

MEMA

Illenberger &

Associates

Environmental Impact Assessment

for the Proposed Nuclear Power

Station (‘Nuclear 1’) and Associated

Infrastructure: Dune Geomorphology

Impact Assessment

2010 This report describes mobile dune sand deposits and potential

environmental impact related to dune dynamics at three proposed sites:

Duinefontein, Bantamsklip, and Thyspunt.

The dune varieties found at Thyspunt are mobile dunefields of the

headland-bypass dunefield variety (e.g., the Oyster Bay dunefield), and

vegetated parabolic dunes and hairpin parabolic dunes. Sidewalls of

previously mobile dunefields form long, vegetated dune ridges. Parts of

the mobile dunefields have been artificially stabilised with alien

vegetation such as Rooikrans.

Surface

Faulting

Assess-

ment

(Yes)

SSC

(No)

Description of dunefields—Thyspunt site area

and vicinity

pp. 25-26

Summary of ages and original references.

Surface fault rupture assessment

Continuity of older dune forms may provide

geomorphic evidence to evaluate presence or

absence of surface rupture in the site area.

Figure 2-10

and 2-11

KLH

Illenberger &

Burkinshaw

The Cape St Francis Headland

Bypass Dune System and Beach

Erosion at St. Francis Bay and

Sediment Accumulation in the

Kromme Estuary

2007

(update

of 2001

report)

Summary of the Cape St Francis headland bypass dune system (Oyster

Bay dunefield and Thysbaai dunefield, a stabilised Santareme dunefield,

and a small headland bypass system that crosses Cape St Francis).

Earlier dunefield activity is manifested by suites of east-west-trending

hairpin parabolic dunes and remnant lateral margins of previous dune

corridors 10–15 m high and fossil dune ridges 20–40 m high).

Surface

Faulting

Assess-

ment

(Yes)


Geochronologic data to assess ages of older

dune formations in Thyspunt site area and

vicinity. Continuity of older dune forms may

provide geomorphic evidence to evaluate

presence or absence of surface rupture in the

KLH


180


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Data Used

in the SSC


Luminescence dating from Oyster Bay dune ridges confirms dune activity

associated with the late Pleistocene interglacials, 105 and 225 ka. Iron-

enriched sands found on the flanks of the fossil ridges were dated to 225

ka (Oyster Bay dunefield) and 490 ka (Thysbaai dunefield).

Impressive suites of larger fossil linear dune ridges, 60–80 m high, that

occur west of Oyster Bay village (Slangbaai) are thought to date back to

at least the middle Pleistocene (1 Ma). West of the Tsitsikamma River,

fossil dunes are probably Pliocene (between 2 and 5 Ma). Cross sections

through the region show that the volume of sand in the fossil dunes

increases as one moves westwards and further back in time.

Aerial photos indicate that Cape St Francis Bay beach has a long history

of variability, going back thousands of years. This is in contrast to most of

the South African coastline, which has been stable. Variability is linked to

sediment pulses when dunes arrive and Kromme River flood events.

North of Kromme River mouth has been more stable.

SSC

(No)

site area.

Illenberger et al. Eastern Cape Coastal Excursion

Guide

1997 Field guide that describes geomorphic landforms and dunes in the

Bathhurst/Port Elizabeth area.

Discussion of the luminescence ages of dunes at Lidney (Stop 6).

Discussion of sea-level changes and impacts on fluvial and marine

deposition is similar to discussion by Hattingh (2001).

No MEMA

Illenberger et al. Luminescence Dating of Coastal

Dunes of the Southern-Eastern Cape

2005 Summary of available dates for Wilderness dune cordon, Cape St

Francis, Point Recife, and Northern Algoa Bay areas.

Wilderness dune cordon: The seaward cordon has a core dating to the

last interglacial and is capped with Holocene dunes (luminescence dating

ages 115 ka and 6.5 ka, respectively). A midden within the Holocene

sequence yielded a radiocarbon age of 2,780 yr. The middle cordon has

a luminescence age of 200 ka, which is interpreted to represent the

second to last interglacial, although the cordon is probably polycyclic like

the seaward cordon. The landward cordon has yielded two infrared-

stimulated luminescence (IRSL) ages: 260 and 1,380 ka.

Cape St Francis headland: Dating of fossil dune ridges at the windward

end of the Oyster Bay dunefield confirmed dune activity associated with

late Pleistocene interglacials. Weathered dune rock from a ridge flank

dated at 105 ka, and case-hardened aeolianite from the downwind nose

of another ridge dated at 225 ka. Iron-enriched sands that form part of

the dune deposits have been dated to 225 and 490 ka, indicating that it

Surface

Faulting

Assess-

ment

(Yes)

SSC

(No)


Geochronologic data to assess ages of older

dune formations in Thyspunt site area and

vicinity. Continuity of older dune forms may

provide geomorphic evidence to evaluate

presence or absence of surface rupture in the

site area.

KLH


181


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Data Used

in the SSC


takes some time to form ferruginous sand of this sort.

Cape Recife: Headland-bypass dunefields have revealed Pleistocene

dunes (184 ka) capped by a well-developed black organic soil with a

radiocarbon age of 1,550 yr, overlain by late Holocene dunes

(luminescence age 320 yr). Along the western shore of Algoa Bay, a

fossil dune ridge (interpreted geomorphologically to be an Eem [last

interglacial] equivalent of the adjacent retention ridge) was dated at 154

ka.

Northern Algoa Bay: What were interpreted in the field as successively

older sites were dated at 62, 107, 25, and 175 ka, indicating possible

mixing of samples in upper part of soil.

Lewis Late Quaternary Climatic Changes,

and Associated Human Responses,

During the Last ~45 000 yr in the

Eastern and Adjoining Western

Cape, South Africa

2008 This article compiled evidence of climatic conditions from ~45 ka to the

present in South Africa. Before 43 ka there were interstadial conditions;

after 24 ka there were stadial conditions. Warming was apparent by~17–

18 ka. The Early Holocene was drier than the Late Holocene. At

Drakensberg, the mid-Holocene was arid.

No Summary figure of radiocarbon sites (Figure 2) KLH

Porat & Botha The Luminescence Chronology of

Dune Development on the

Maputaland Coastal Plain, Southeast

Africa

2008 p. 1024—

This paper presents geomorphologic and lithostratigraphic mapping of

dune systems on the Maputaland coastal plain of NE KwaZulu-Natal

Province. Weathered dune and interdune wetland sediments spanning

from before MIS 11 to MIS 7 underlie the coastal plain. At least two

generations of decalcified aeolianite of MIS 5 and 4 form the core of the

complex coastal barrier dune. On the coastal plain, frequent sand

mobilisation events during MIS 3 and 2 resulted in the development of

discrete complexes of highly extended, northward-directed parabolic

dune systems and reworking of the crest of the central sand mega-ridge.

During the Holocene transgression, at least four laterally extensive

complex transverse ridges of coalesced ascending parabolic dunes

accreted against the aeolianite core of the coastal barrier.

p. 1040—

Reference is made to luminescence dates from Cape St Francis

headland bypass dunes (225 ka) and Cape Recife / Driftsands headland

bypass dunes (184 ka) (Illenberger et al., 1997; Bateman et al., 2004).

No KLH

Roberts et al. Last Interglacial Fossil Elephant

Trackways Dated by OSL/AAR in

Coastal Aeolianites, Still Bay, South

2008 This paper describes the Pleistocene aeolianite exposures at Still Bay,

which represent the recently eroded remnants of a dune cordon, mainly

built by coalesced parabolic dune systems. The optically stimulated

No Quaternary geochronology related to aeolianites

and palaeoclimate during MIS 5 in South Africa.

KLH


182


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Data Used

in the SSC


Africa luminescence (OSL) and amino acid racemisation (AAR) dating

demonstrate ages ranging from MIS 5e to 5b and termination of

Pleistocene aeolian sedimentation at ~90 ka. The Pleistocene aeolianite

is separated from the overlying Holocene dunes (dated to ~8 ka) by a

major hiatus recorded by a horizon of intense pedogenesis.

The presence of Loxodonta africana at Still Bay represents the

southernmost occurrence of this species recorded to date and, possibly,

a closer proximity of woodland during MIS 5. This and other observations

may indicate a higher moisture regime than at present.

Dune sedimentation coincided with transgressive maxima and early

regression (i.e., proximity of a sandy beach was the overriding control),

as at the present time.

AAR also demonstrated a notable reworking of bioclasts from older, pre-

MIS 5 dunes into the Still Bay aeolianite succession.

Roberts et al. West Coast Dune Plumes: Climate

Driven Contrasts in Dunefield

Morphogenesis Along the Western

and Southern South African Coasts

2009 This paper describes two major late Quaternary coastal dune systems,

the False Bay and Duinefontein dune plumes.

At False Bay, three generations (transgressive/early regressive cycles) of

dune deposition, corresponding to MIS 7, MIS 5, and Holocene were

resolved. The Duinefontein plume is dominated by MIS 5 and Holocene

sedimentation. Glacial periods are marked by the development of mature

palaeosols.

False Bay—MIS 7.

Marginal marine lagoonal/estuarine sandy clays and peats (Barwis &

Tankard, 1983) and shelly deposits encountered in the boreholes indicate

a maximum MIS 7 highstand just below present mean sea level.

p. 37—

Discusses major morphogenetic dunefield types: dune plumes that

penetrate far inland from source beaches typify the western coast. A

series of shoreline-parallel dune cordons that mimic strandline

configurations are commonly developed on the southern coast.

MIS 5 dune plumes appear to be more limited than their middle

Pleistocene and Holocene counterparts. The authors speculate that a

weaker South Atlantic Anticyclone at this time may reflect a weakened

meridional pressure gradient due to reduced Antarctic sea ice during the

warmer MIS 5e.

No Low rates of vertical crustal deformation in the

region

p. 25

Notes that a passive intraplate, trailing-edge

tectono-seismic model has been determined for

the mid-latitude southern African coastline,

which is also removed from glacio-isostatic

influence (Tyson, 1999; Goedhart, 2007; Jacobs

& Roberts, 2009). Consequently, rates of

vertical crustal deformation are low, and

Quaternary shoreline datums chiefly reflect

glacio-eustatic sea levels.

MIS 7 palaeosea level of just below present

mean sea level.

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_T4

KLH

Siesser Relict Algal Nodules (Rhodolites) 1972 Abstract— No KLH


183


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Data Used

in the SSC


from South African Continental Shelf Relict algal nodules (rhodolites), which average about 5 cm in diameter,

have been found in abundance at one locality on the South African

continental shelf. Nodules dredged from 115 and 120 m water depths

have been dated at 13,670 ± 120 and 12,990 + 100 yr BP, respectively..

p. 616—

Algal nodules are abundant south of Cape St Francis only and have not

been recovered from other parts of the southern continental shelf. This

restricted occurrence probably results from an incursion of warmer

waters into this locality during the Flandrian transgression, allowing the

nodules to form in shallow, agitated waters. The progressive and rapid

rise in sea level subsequently left behind a relict algal-nodule deposit.

Marine Terraces—Palaeosea Level (see also Hanson et al. 2012a for additional references and discussion of marine terrace studies and palaeosea-level data).

Bateman et al. A Dating Intercomparison Study on

Late Stone Age Coastal Midden

Deposits, South Africa

2008 This study uses amino acid racemisation, OSL, and radiocarbon analysis

to date shell middens. The three forms of dating get similar results.

No GIS_S0030

_F1

KLH

Bierman Report #2, Cosmogenic

Geochronology, Southern Africa

Southern Coast Marine Terraces

2012 Appendix E1 in Hanson et al. (2012a), Thyspunt Geological

Investigations—Marine Terrace Studies. This study measured in situ–

produced cosmogenic 10Be in 62 samples, and 26Al in a subset of these

samples. Places numerical age constraints on the exposure age and

minimum total (exposure plus burial) histories of outcrops on marine

terrace surfaces, as well as buried gravels (littoral and or fluvial) in south-

central South Africa.


Bowen Sea Level ~400,000 Years Ago (MIS

11): Analogue for Present and

Future Sea-Level?

2010 Abstract—

Estimates of the original sea level of MIS 11 (~406 ka), based on

average uplift rates of the “last interglacial” sea level (MIS 5.5) using a

range of estimates for sea level (2 to 6 m) and and a range of ages for

the sea level highstand (116 124, and 132 ka ), do not support the

hypothesis of an MIS 11 sea level at ~20 m, and instead show that it was

closer to its present level.

p. 25—

An MIS 11 sea level close to the present sea level is consistent with

inferences drawn from benthic oxygen isotope stratigraphy (McManus et

al., 2003) and lies within the band of sea levels similarly estimated by

Waelbroeck et al. (2002).

The melting of Northern Hemisphere mid-latitude ice sheets at their

greatest extent during MIS 12 (McManus et al., 1999) yielded the

No MIS sea level at 1.5 ± 3 m.

Mean sea-level calculation for MIS 11.3 is 3 ± 4

m, but if outliers at two standard deviations or

greater are removed, the mean value is reduced

to 1.5 ± 3 m.

p. 24

Estimates of MIS 11 sea levels based on uplift

correction from an MIS 5.5 sea level at 6 m tend

to lie on the higher side although none exceed

~9 m.

Note: In a discussion of this paper by Hearty

(2010), the overall methodology was

questioned, and it was noted that many

appropriate references were not cited and a

KLH


184


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Data Used

in the SSC


greatest transfer of continental ice volume to the oceans of the last 0.5

Myr. MIS 11 lasted over 60 kyr and was the longest interglacial of the last

0.5 Myr (Loutre & Berger, 2003).

number of reference citations were inaccurate

or missing.

Brynard et al. Report on Mineralogical Investigation

of Samples from Thyspunt and De

Hoek near Humansdorp

1988 Examines the mineralogy of quartzite from coastal outcrops of the

Tchando, Kouga, and Peninsula Formations.


Carr, Bateman, et

al.

The Last Interglacial Sea-Level High

Stand on the Southern Cape

Coastline of South Africa

2010 This paper provides rigorous numerical age constraints for the last

interglacial sea-level fluctuations in the southern Africa coastline region.

Deposits in the Swartvlei and Groot Brak Estuaries display tidal inlet

facies overlain by shoreface or aeolian facies. Contemporary facies

relations suggest a probable highstand 6.0–8.5 m above modern sea

level (amsl). At Cape Agulhas, a past sea-level highstand comprises a

gravel beach (~ 3.8 m above MSL) and an overlying sandy shoreface

facies (up to 7.5 m above MSL). OSL ages between 138 ± 7 ka and 118

± 7 ka confirm a last interglacial age for all marginal marine facies.

The highstand was followed by a sea-level regression that was

associated with aeolian dunes dating to between 122 ± 7 ka and 113 ± 6

ka.

No Regional marine terrace correlations

The elevation and ages of marine highstand

deposits provide a regional framework for

comparison to marine terrace shoreline angles

identified as part of the marine terrace

investigations conducted for the Thyspunt site

characterisation.

GIS_S0028

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GIS_T0028_

T2

KLH

Carr, Boom, et al. New Evidence for the Age and

Palaeoecology of the Knysna

Formation, South Africa

2010 This study dates lignite deposits (Knysna Formation) to at least 1.7 Ma. No GIS_D0067

_F1

LG

Compton Holocene Sea-Level Fluctuations

Inferred from the Evolution of

Depositional Environments of the

Southern Langebaan Lagoon Salt

Marsh, South Africa

2001 A Holocene sea-level curve is constructed from the facies distribution and

radiocarbon ages of sediment recovered from the distal, southern salt

marsh of Langebaan Lagoon. Calibrated radiocarbon analyses of an

oyster-rich bioclastic gravel indicate that the Flandrian Transgression

flooded the lagoon to 0–3 m above present-day levels by 6.8 ka. Organic

matter and shell material dated in distal lagoonal sediments indicate that

sea level returned to present-day levels by 4.9 ka and have since

remained within 61 m of present-day levels. Bleached shell and a hiatus

in sedimentation suggest a ~1 m sea-level lowstand between 2.5 and 1.8

ka. There also was a 0.5 m sea-level highstand at 1.3 ka followed by a

0.5 m lowstand at 0.7 ka.

No Error bars of ~50 cm should probably be added

to the curve based on the type of burrowing

crustaceans present and use of bulk organics.

Sea level curve seems to add more weight to

other authors’ ages than their own.

MEMA

Compton Pleistocene Sea-Level Fluctuations

and Human Evolution on the

Southern Coastal Plain of South

Africa

2011 This paper proposes that the southern coastal plain (SCP) of South

Africa may have served as a geographical point of origin through periodic

expansion and contraction (isolation) in response to glacial/interglacial

changes in sea level and climate.

No Provides some context for human artifacts that

may occur in fluvial or marine terraces in the

region.

-- KLH


185


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Data Used

in the SSC


Provides age ranges for the following:

Early Stone Age large bifacial hand axe of the Acheulean artifact

assemblage type—from 1,800 ka.

Largely hafted, finer stone tools of the Middle Stone Age—between 600

and 250 ka.

Anatomically modern humans—by 200 to 155 ka.

The SCP of South Africa was potentially isolated from the rest of Africa

during interglacial periods when sea level was above –75 m and the

Hangklip and Plettenberg Bay portals were closed, as well as during

glacial maxima when a wet, expanded SCP may have served as a refuge

from a dry interior.

Compton &

Franceschini

Holocene Geoarchaeology of the

Sixteen Mile Beach Barrier Dunes in

the Western Cape, South Africa

2005

This study used radiocarbon dating to determine the Holocene history of

dunes near Yzerfontein and Saldanha Bay. The study dated bulk sand,

gull-dropped mussel shells and manuports and concluded there were

three phases of shoreline progradation that corresponded to drops in sea

level at 5.9, 4.5 and 2.4 ka.

No MEMA

Craig Landscape Evolution of the Garden

Route Between the Bloukrans River

and Alexandria Coastal Dunefield

1997 This thesis maps coastal geomorphology from the Bloukrans River to the

Alexandria Dunefield. The thesis concludes that there is little to no

evidence of post-Miocene deformation in the region based on a

consistent height of the interpreted Miocene shoreline angle at 260 to

280 m amsl and no evidence for tilting. The study uses the chronology of

Partridge & Maude (1987) and is part of a two part study of the southern

coast. The other half of the work is presented by Van Zyl (1997).

This study maps six surfaces: African terrestrial, African marine, lower

fluvial, lower marine, the grass ridge plateau and the Coega platform.

The latter two surfaces were only found in the Algoa Bay region.

The shape of the relict sea cliffs indicates that the palaeobays were also

log-spiral bays like the modern bays.

In Jeffries Bay and other locations, palaeosea cliffs are masked by

modern and ancient dune sands.

There are two types of river valleys in the study area: juvenile and

incised. Juvenile valleys are more recent features and do not have steep

walls. Incised valleys formed through down cutting during the sea level

variation of the Plio-Pleistocene and are not the result of tectonic uplift.

No MEMA

Davies Pleistocene Shorelines in the

Southern and South-Eastern Cape

1971 p. 185—

Algoa to St Francis, marine terraces up to more than 300 m.

Yes

(Indirectly)

Regional marine terrace correlations

Evidence for apparent lack of vertical

MEMA/ KLH


186


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Data Used

in the SSC


Province (Part 1) Tsitsikamma and Outeniqua—Marine gravels right at the summit of the

coast scarp.

Riversdale region—West of Mossel Bay behind the calcified dunes is a

series of marine gravels that can be traced up gentle slopes.

p. 186—

The most primitive hand axes are in beach gravels at ~60 m.

There is a long stretch of coastline without the 60 m terrace south of

Lupatana.

p. 189—

In Natal, there is no evidence for a marine level at 48 m, and there is a

doubtful one at 38 m.

In Transkei, there is no evidence for a marine level between 30 and 60

m.

Between Hagahaga and the Great Fish River, there is no convincing 48

m terrace.

p. 194—

Good 9 m and 6 m terraces from River Kei to Port Edward.

p. 203—

Along the Gamtoos and Seeikoi Rivers, probable estuarine terraces at

Uitkyk, 55 m (site 501) and perhaps 67 m (site 436); the Glen at 61 m

extending towards Jeffreys Bay (site 409).

p. 212—

Cliff at Plettenberg Bay with pebbles next to it is probably due to faulting

and is not marine (site 340).

No trace of high-level beaches was found at Knysna Heads or at Noetsie;

the west coast of Plettenberg Bay was not visited.

p. 220—

Pebbles without a cliff at 142 m at Uitkyk (site 136).

deformation based on older marine terraces of

Pliocene to early Quaternary age.

Constraints on presence/absence of vertical

deformation (Worcester, Gamtoos, Cape St

Francis, and Coega Faults).


Southern and South-Eastern Cape

Province (Part 2)

1972 Abstract—

Shorelines at 18, 9, 6, 3.5, and 1.5 MSL. Isotopic dates suggest that the

6 m terrace is from the Wurm interstadial. The 9 m terrace almost

certainly dates to the Eemian. The 1.5 m terrace dates to after 2,000 yr

BP, and the 3.5 m terrace dates to ~5,000 yr BP.

p. 232—

Cape Recife near Skoenmakerskop (sites 513, 514), beachrock at 15

and 18 m, overlain by dune sand.

Yes Regional marine terrace correlations

Constraints on presence/absence of vertical

deformation (Worcester, Gamtoos, Cape St

Francis, and Coega Faults)

Ages and locations of marine terraces

Only notes from Cape Recife to George. More

sites are covered in the article.

Terrace elevations higher than 18 m are

MEMA/ KLH


187


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in the SSC


Above the Gamtoos River at Mondplaas store (site 502), an estuarine

terrace up to 18 m. The terrace continues upstream.

Between Gamtoos and Kromme, no observations of the 18 m terrace;

possibly, it is masked by dune.

Traces of a rock terrace at 18 m in the gap between dunes on Cape St

Francis (site 426). On Seal Point, a notched cliff base (site 418). Traces

of a terrace with cliff east of Oyster Bay (site 402).

Tsitsikamma cliffs—Krige (1927) identified cliffs with an 18 m base. West

of the Storms River mouth narrow terrace traces at 19 m near Swartrif

(site 309).

p. 233—

West of Keurboomstrand Hotel,18 m beach with laid pebbles at 18 m

(site 327).

p. 234—

Between Bietou River mouth and Diep River, a promontory with a scarp

composed of pebbles at 15 m but rising westwards to at least 18 m (site

336).

Knysna probable terrace fragment at 18 m (site 359); cave at ~18 m at

Coney Glen (site 353).

Between Knysna and George, the only evidence at ~18 m is marine or

estuarine gravel on a ~21 m planed terrace on both banks of the

Goukamma River (site 205).

Frog Rock—Beach fragment at 17.4 m asl (site 253).

p. 237—

Two stages of “Minor Emergence” identified by Krige (1927), at 6 and 9

m.

p. 239—

Humewood/Happy Valley—Rock platform at 9 m (site 526).

p. 240—

Shells at 10 m, calcified beach at 9 m; lower platform at 6 m (sites 430–

432).

Kromme River mouth—Rock-cut terraces at 9 m and 6 m (sites 413–

415).

Seal Point—Narrow terraces with notched cliffs at 9 and 6 m (sites 419–

420).

Oyster Bay and White Point—Terraces with cliffs at 9 and 6 m (sites 403,

typically based on the presence of pebbles, the

maximum and minimum height of which could

not be traced.


188


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in the SSC


437).

Tsitsikamma East—Cave-floor beach deposit at 7.8 m (site 406); rock

surface at 6.3 m.

Hengelaarskroonstrand—Terraces at 9 and 6.6 m (sites 410–411).

Storms River mouth—Terrace at 9 m (site 313); cave at 9 m (site 305);

cliff at 6 m (site 311).

p. 241—

Plettenberg Bay—Trace of shoreline at 9 m (site 323).

Keurbooms Estuary—6–9 m shingle-bar (site 335).

Noetsie—Terrace at 9 m (site 348) probable terrace at 6 m.

Knyssa—Cave floors at 6 and 10.5 m (site 360) and at 6 and 9 m (site

358-7). Terrace fragment with notch at 6 m at Coney Glen (site 354).

Wilderness terrace at 4.5 m (site 212) now destroyed beach at 6–7.5 m

(site 210).

Pacaltsdorp—6 m terrace (sites 215, 214, 219), cave at 9 m.

p. 242—

Mossel Bay caves at 9 m (site 260); 6 m caves (site 252).

p. 256—

Most of Gamtoos floodplain was part of the sea until recently. Older

marine beds have been found on a road-cutting close to Mouritzkraal.

Unconformity at 4.5 m, below which are silty clays with Donax (marine

clam), and above which are fine sands with Assiminea (brackish snail).

Nearby is a terrace at 9 m.

p. 265—

Gamtoos—4.4 km from current river mouth, pilings for the new bridge

revealed hard sandstone at –47 m below river level (+2 to +3 m MSL),

boulder bed at –32 m, and shells in sand at –9 m (reference uncertain,

probably below surface). Shells included Turritella capensis and

Crassostrea sp. Wood sample from –9 m MSL age of 1,170 ± 50 yr BP.

Sand topped by clay.

Author only kept track of locations with both 3.5 and 1.5 m sea-level

indicators. Some locations that had one or the other are not mentioned in

the article.

p. 269—

Maitland mouth—The camping site is an estuarine terrace at 4.2 m,

probably associated with the 3.5 m sea level.


189


Are the

Data Used

in the SSC


Gamtoos—Close to the mouth of the river are remains of a beach at 1.5

m (site 505). An estuarine floodplain extends down the valley, dipping

gently from 3.3 m above river at the bridge (site 504) towards the mouth.

Abrasion platforms were observed at roughly +0.6 m (3 sites); +0.3 m (1

site); 0 m (4 sites); –0.6 m (7 sites); –0.9 m (1 site).


Western Cape and South-West

Africa

1973 p. 736—

Widespread evidence for river terraces and gravel along the Olifants

River below Vredendal. The principal terrace gravel is the Canal Gravels.

The elevation of these gravels is 42 m above the river and nearly 61 m

amsl.

p. 739—

Canal Gravels are correlated to the 30 m sea level.

The 18 m sea level must be contemporary with a wide rock terrace at

about 15 m above the river at Ebenhaeser Mission below Platzkraal

(W43). A 9 m terrace near Vredendal may also be contemporary.

p. 740

Below Platzkraal, the river is incised into a floodplain 3–3.5 m high.

There are gravels higher than the Canal Gravels.

p. 751—

Between the Orange River and Walvis Bay are a series of shorelines that

can be traced for up to 80 km. They are named A through D, with A at 3–

4 m, B at 8 m, C at 13 m, and D at 30–20 m.

Along stretches of the coast with diamond mining, little new work was

done.

No This document records information on depth to

bedrock for the western coast of South Africa.


MEMA

Deacon &

Geleijnse

The Stratigraphy and Sedimentology

of the Main Site Sequence, Klasies

River, South Africa

1988 Hendey & Volman (1986) argue that, based on the size of stalagmites,

the Klasies River site provides no evidence for a sea level as high as 6–8

m in the last interglacial period. This earliest phase of speleothem

formation cannot be telescoped in time into the last interglacial interval

and be of the same age as the overlying deposits that are more securely

dated to the beginning of this interval.

No LG

Erlanger Rock Uplift, Erosion, and Tectonic

Uplift of South Africa Determined

with Cosmogenic 26Aluminum and

10Beryllium

2010 The outcrop of a marine terrace recently exposed by a construction

project near the Greenwood Park Railway Station in Durban was

correlated to the “70-m bench” of Davies (1970). The elevation was

measured by Erlanger at 65.1 m asl. Twelve sandstone clasts collected

from a gravel layer that lies 4.3 m below the terrace tread yielded a burial

age of 4.26 ± 0.68 Ma. Sea-level reconstructions at this time place early

Yes

(Indirectly)


Regional uplift rates

KLH


190


Are the

Data Used

in the SSC


to mid-Pliocene sea level at 20–30 m. Correcting for this eustatic sea

level results in a rock uplift rate of 10 ± 3 m/Ma. With no correction, the

uplift rate is 16.9 ± 1.2 m/Ma.

Erlanger et al. Rock Uplift Rates in South Africa

from Isochron Burial Dating of Fluvial

and Marine Terraces

2012 This manuscript focuses on the Sunday’s River terraces and Durban

marine terrace portion of Erlanger’s 2010 Master’s thesis. Most data is

the same except the calculated uplift rates. New rates (vs thesis) are 16.1

± 1.3 m/my over 4 my (vs, 16.9 ± 1.2 m/my) for t he Sunday’s River

region and 9.4 ± 2.2 m/my (vs. 10 ±3 m/my) for Durban.

Yes

(Indirectly)


Regional uplift rates

MEMA/ KLH

Fisher et al. Middle and Late Pleistocene

Paleoscape Modeling Along the

Southern Coast of South Africa

2010 Provides a beginning palaeoscape model for Pinnacle Point near Mossel

Bay made by modelling coastline distances based on eustatic changes in

sea-level. The article discusses how coastline and sea-level changes

influenced human behavioral evolution along the southern coast of Africa.

Using integrated bathymetric data sets, GIS, and a relative sea-level

curve, the authors estimate the position of the coastline at 1.5 ka

increments over the last ~420 kyr and compare model predictions to

strontium isotope ratios from speleothems as an independent check.

No Palaeosea-level indicators

Coastal caves (more than 20) occur in nearly

vertical cliffs; cave floors cluster at two heights

(+3–7 m and +12–15 m).

As van Andel (1989) notes, the MIS 5e beach

has been measured at ~4–6 m amsl throughout

the South African coast (see also Marker 1984,

1987).

GIS_S0029

_F1

GIS_D0029

_F1

KLH

Forman Optical Ages for Aeolian and Littoral

Sediments from Drill-Core, Eastern

Cape, South Africa

2012 Appendix E2 in Hanson et al. (2012a), Thyspunt Geological

Investigations—Marine Terrace Studies. Uses OSL dating to determine

the ages of sediments associated with marine terraces near the Thyspunt

site.


Franceschini &

Compton

Aeolian and Marine Deposits of the

Tabakbaai Quarry Area, Western

Cape, South Africa

2004 No GIS_D0066

_F2

LG

Hagedorn Silcretes in the Western Little Karoo

and Their Relation to

Geomorphology and Paleoecology

1988 Preliminary results of two electron spin resonance tests have proved an

age of 7.3 and 9.4 Ma. Likely formed in an arid-to-semi-arid environment

Yes Kango Fault (8.4.1) characterisation

Age of silcretes formed in high pediment (Tg )

surfaces displaced by Kango Fault.

MEMA/ KLH

Hanson et al. Thyspunt Geological

Investigations—Marine Terrace

Studies

2012a Summarises and compiles data from previous coastal studies in southern

Africa, in addition to performing new studies of marine terraces, such as

coring, dating, and coastal surveying.

Yes Seismogenic Probability of the Plettenberg Fault

(8.4.4)

Hearty Comment on “Sea Level ~400,00

Years Ago (MIS 11): Analogue for

Present and Future Sea Level?” by

D.Q. Bowen (2010)—Can the

Extrapolation of Uplift Rates from

MIS 5e Shorelines to MIS 11

Replace Direct and Tangible

2010 Notes that the stratigraphy observed in Bermuda and the Bahamas

reveals multiple MIS 11 stillstands at +2 to 3 m and +7 to 8 m, and a final

peak at +20 m, with the intermediate highstand the most prolonged

event. Bowen (2010) does not incorporate this range of observations into

his model.

No LG


191


Are the

Data Used

in the SSC


Evidence of the Latter’s Sea-Level

History?

Hendey Geological Succession at

Langebaanweg, Cape Province, and

Global Events of the Late Tertiary

1981 Attributes the Tertiary marine terrace record of Langebaanweg to global

transgressions correlated to sea-level changes in the Mediterranean. The

Messinian event (6.6–5.2 Ma) is a period of drying of the Mediterranean

associated with the expansion of the Antarctic ice cap during the terminal

Miocene. It was terminated in the early Pliocene by a marine

transgression ~4.5 Ma.

Marine and terrestrial deposits of the Elandsfontein Formation occur up

to +30 m in the subsurface and are correlated with the Early-to-Middle

Miocene transgression.

The lowermost Gravel Member consists of phosphatic rock

corresponding to a +30 m stillstand. It is interpreted as a regressive

deposit emplaced during the pre-terminal Miocene.

The Quartzose Sand Member of the Varswater Formation was

interpreted as an estuarine complex laid down during an early stage in

the early Pliocene transgression.

The Pelletal Phosphorite Member of the Varswater Formation was

interpreted as marine and fluviatile phosphatic rocks laid down during the

Pliocene transgression.

The Calcareous Sand Member of the Varswater Formation is interpreted

as a coastal barrier complex laid down during the latter stages of the

early Pliocene transgression contemporaneously with the Pelletel

Phosphorite Member at elevations up to +80 m.

Anyskop terrestrial deposits up to +50 m in elevation are associated with

a late Pliocene stillstand.

Baard’s Quarry fluviatile deposits occur at 20 m at 1.9 Ma.

No Subsequent work by Pether (1986) reinterprets

this sequence in terms of prograding

regressional deposits.

LG

Hendey &

Volman

Last Interglacial Sea Levels and

Coastal Caves in the Cape Province,

South Africa

1986 This paper suggests that the 6–8 m shoreline in southern Africa dates

back to an early Pleistocene interglaciation with an age on the order of 1–

1.5 Ma. The successions in the caves at Klasies River mouth and Die

Kelders, which has been interpreted to be last interglacial in age, are

assessed to be pre-last interglacial. These sites, along with Herolds Bay

Cave, indicate that in southern Africa, the only last interglacial shoreline

above present sea level is at ~4 m, and it dates from MIS 5e.

With regard to the 6–8 m terrace, middle Pleistocene fossils and

Acheulean artifacts found, respectively, at Duinefontein and Bok Baai

No Palaeosea-level indicators

Age of 6–8 m terrace

The conclusions do not appear to be consistent

with more recent studies (e.g., Roberts et al.,

2009).

KLH


192


Are the

Data Used

in the SSC


north of Cape Town postdate this shoreline and prove that it can be no

younger than late middle Pleistocene.

Mammalian fossils from the Port Durnford Formation in Zululand (6–8 m

succession) confirm a deposit age before the last interglacial age.

Jacobs &

Thwaites

Erosion Surfaces in the Southern

Cape, South Africa

1988 p. 51—

Apart from the pronounced coastal platform at 150–215 m, there is still

controversy about the higher erosion levels and their characterisation and

nomenclature. At least two higher levels have been identified whose

altitudes overlap. The dating depends on the age of the coastal

limestones, silcretes, and lignites, and on local tectonics.

p. 52—

In contrast to the inland silcretes, the coastal formations are associated

with deep weathering profiles formed in broad, shallow valleys under a

humic tropical or subtropical climate. The lack of such topography on the

De Vlugt plateau may explain why silcretes have not developed here.

Two datings of silcrete just north of the Langeberg outside the coastal

plateau in the Little Karoo proved an age of 7.3 and 4.4 Ma (Hagedorn,

1988).

Three erosional surfaces have been identified on the Southern Cape. All

of them were formed by sub-aerial processes, although a marine

influence in the Tsitsikamma region may have preceded this.

Preliminary datings of the lignites (as Miocene) situated between the

main and next higher platform support the hypothesis that the higher-

level surfaces are pre-Miocene, possibly as old as mid-Cretaceous, while

the main platform is Miocene/Pliocene with upheaval in the Pliocene.

No Reference to age of silcrete MEMA

Jacobs et al. Development of the SAR TT-OSL

Procedure for Dating Middle

Pleistocene Dune and Shallow

Marine Deposits Along the Southern

Cape Coast of South Africa

2011 Discusses the use of the thermally transferred (TT) OSL dating method at

three sites near Mossel Bay: Klein Brak River, Dana Bay, and Hartenbos.

The weighted mean age of samples collected from different units in the

successions is MIS 11. The samples have grand weighted mean ages of

389 ± 14 ka (Klein Brak River), 388 ± 14 ka (Dana Bay), and 370 ± 18 ka

(Hartenbos).

No Regional marine terrace correlation

LG

Le Roux Lithostratigraphy of the Alexandria

Formation

1987 Description of the Alexandria Formation. No Seismotectonic Setting (Chap. 4) GIS_D0061

_F2

LG/ KLH

Le Roux The Lithostratigraphy of Cenozoic

Deposits Along the South-East Cape

Coast as Related to Sea-Level

1989a The Eocene Bathhurst Formation consists of calcareous sandstone,

conglomerate, and limestone deposited on a marine planation surface up

to 360 m in elevation.


Regional marine terrace correlation

LG/ KLH


193


Are the

Data Used

in the SSC


Changes The Alexandria Formation consists of Miocene to Pliocene alternating

layers of calcareous sandstone, conglomerate, and coquinite deposited

on well-planed seaward-sloping platforms of Miocene to Pliocene age.

Depositional environments range from shoreface and foreshore to

lagoonal and/or estuarine.

The northern limit of the Alexandria Formation roughly coincides with the

300 m contour in the area west of the Kowie River. The Suurkop

stratotype at Addo Park occurs at an elevation of 290 m and is probably

Miocene in age. The Blaawbaadjiesvlei stratotype occurs at an elevation

of 240 m and is probably of Miocene age. The Aluinkrantz stratotype

occurs at an elevation of 220 m and is probably of Miocene age.

The Salnova Formation is situated on wave-cut surfaces thought to

represent highstands of sea level during one or more Quaternary

interglacials. It consists of fine- to coarse-grained calcareous sand/-

sandstone, gravel/conglomerate, shelly limestone, and coquina, all of

which are marine or estuarine in origin.

The Salnova Formation is an intertidal deposit ranging from the sandy

beach environment to a rocky shore environment. The formation reflects

higher stands of sea level during Quaternary eustatic movements up to

20 m in elevation. Outcrops of marine material are observed below 20 m

along the rocky coast at Keurbooms, Knysna, Sedgefield, Klein Brak, and

Hartenbos.

Le Roux Lithostratigraphy of the Nahoon

Formation

1989b Provides locations and descriptions for type localities of the aeolian

Nahoon Formation.


GIS_D0062

_F2

LG

Le Roux Lithostratigraphy of the Salnova

Formation

1991 Provides locations and descriptions for type localities of the marine

Salnova Formation.

No Digitised locations of observed Salnova

Formation do not have interpretations of

elevation of sea level.

GIS_D0064

_F32

LG

Le Roux Lithostratigraphy of the Nanaga

Formation (Algoa Group)

1992 Provides locations and descriptions for type localities of the aeolian

Nanaga Formation.

No GIS_D0065

_F4

LG

Malan The Bredasdorp Group in the Area

Between Gans Bay and Mossel Bay

1987 Abstract—

The Bredasdorp Group consists of limestone, sandy limestone,

sandstone, and conglomerate in five different formations. The limestone

extends up to 15 km inland.

p. 506—

De Hoopville Formation—Consists of Mio-Pliocene marine deposits.

Described as a shelly quartzose sand and oyster-bearing conglomerate.

No Regional marine terrace correlation MEMA


194


Are the

Data Used

in the SSC


Contains some beach facies.

Wankoe Formation—Consists of Mio-Pliocene consolidated aeolianite.

Up to 290 m thick.

Rooikrans Formation—Consists of Pleistocene shelly quartzose sand

and conglomerate. Only partially consolidated.

Waenhuiskrans Formation—Consists of Pleistocene semiconsolidated

aeolianite. Forms a band along the coast.

Strandveld Formation—Consists of Holocene unconsolidated windblown

dunes. Occurs directly along the shoreline and includes the active dunes.

p. 507—

Three major transgression-regression cycles can be recognised from the

Tertiary to Recent.

Malan The Stratigraphy and Sedimentology

of the Bredasdorp Group, Southern

Cape Province, South Africa

1990 Confirms marine nature of the Cretaceous “African erosion surface”. No

other Cretaceous silcretes contain evidence of marine deposition.

A 120–140 m bench in the George-Knysna area corresponds to the

Middle Miocene transgression and the related Post-African I erosion

cycle. All pre–Middle Miocene surfaces south of the Langeberg

Mountains were probably formed by sub-aerial processes and were not

related to marine erosion.

Deposition of the De Hoopvlei Formation took place during the Pliocene

regressive phase from a transgressive maximum of 120 m. The basal De

Hoopvlei Formation is correlated with the Alexandria Formation based on

mollusk content and height above sea level.

Deep incision of the coastal platform resulted from a late Pliocene uplift

introducing the Post-African II cycle of erosion. Alluvial terraces at 45 m

above present river level are thought to predate the late Pliocene

regression responsible for the last major phase of river incision.

The 50 m terrace observed around Mossel Bay may be early

Pleistocene.

A 30 m shoreline at Hermanus and Kleinmond may be early Pleistocene

in age. The De Hoopvlei and Wankoe Formations are eroded up to a high

of 35 m.

Yes Regional marine terrace correlation.

Gamtoos Fault (8.4.3) activity

GIS_S0081

_F09

LG/ KLH

Marker A Note on Marine Benches of the

Southern Cape

1987 Examines marine benches based on rock type and offshore gradient.

Benches occur over a wide area and are not local. The study area is near

Knysna.

Coastal Platform at 200 m; notches at 125 m, and between 60 and 80 m;

No Marine Terrace table MEMA


195


Are the

Data Used

in the SSC


boulder beach at 12–14 m. The lower 3 m berm is partially dragged down

by current storm waves.

Maud & Botha Deposits of South Eastern and

Southern Coasts

2000 Describes the stratigraphy of the Algoa and Bredasdorp Groups. No Seismotectonic Setting (Chap. 4) Superseded

by Roberts et al. (2006).

KLH

Nolte Structure and Tectonostratigraphy of

the Gamtoos Belt Between

Tweewaters and Classen Point,

Eastern Cape Province, R.S.A.

1990 p. 42—

Unconformable, scattered high-level terrace deposits that may be partly

coeval with the Alexandria Formation; the oldest deposits could be

outliers or equivalents of the early Tertiary Grahamstown or Martindale

Formations. The deposits consist of sandstone and quartzite blocks

cemented by siliceous or ferruginous material. Up to 40 m thick, but

generally <6 m thick. Terraces generally capped with silcrete.

p. 43—

The Gamtoos Belt along the coast is often covered by strata of the Algoa

Group. The northern limit of the formation roughly coincides with the 300

m contour, above which coeval silcrete or high-level fluvial gravels occur

that are presumably of Tertiary age. The Alexandria Formation (littoral)

has an unconformable lower contact occurring at Claaskraal 26 and

Yellowwoods estate 493.

Yes Characterisation of Gamtoos Fault (8.4.3) GIS_S0078 MEMA/ KLH

Pedoja et al. Relative Sea-Level Fall Since the

Last Interglacial Stage: Are Coasts

Uplifting Worldwide?

2011 The results of this study are based on a worldwide compilation of 890

records of palaeoshoreline sequences, with emphasis on MIS 5e (~122

ka). Most coastal segments have risen relative to sea level with a mean

uplift rate higher than 0.2 mm/yr. The uplift rate is faster on average for

active margins than for passive margins. Neither dynamic topography nor

glacio-hydro-isostasy may explain sustained uplift of all margins.

The authors suggest that only plate-tectonic processes reconcile all

observations of Quaternary coastal uplift. The authors propose that long-

term continental accretion has led to compression of continental plates

and uplift of their margins.

Yes

(Indirectly

explains

regional

uplift)

Supplemental information provides summary of

MIS 5e sea-level data for six locations in South

Africa.

Good discussion of the following mechanisms

that could give rise to the apparent uplift of

continental margins worldwide:

Eustasy: MIS 5e estimates are 3 ± 1 m (Siddall

et al., 2006) and 7.2 ± 1.3 m (Kopp et al., 2009).

Eustatic variations for older isotopic stages

indicate that Quaternary highstands MIS 7, MIS

9, and MIS 11 never exceeded +10 m, leaving

MIS 5e the last highest sea-level stand.

Glacio-hydro-isostasy (g-h-i): Observations and

models suggest that the relaxation occurs within

a few thousand years, even at low harmonic

degrees (e.g., Peltier, 2004). Therefore, even

the effects of the most recent g-h-I event (at ~6

ka) are decreasing. Observations suggest that

KLH


196


Are the

Data Used

in the SSC


this mechanism cannot explain worldwide uplift

pattern and rate.

Dynamic topography (the response of the

surface of the Earth to mantle flow): Controls

absolute and relative sea level at typical rates of

0.001 to 0.01 mm/yr. This effect is too small to

explain global patterns.

Plate tectonics: The average magnitude of

compressive stress has most likely increased in

the lithosphere, as evidenced by tectonic

inversion and accompanying long-term

exhumation of passive margins (Johnson et al.,

2008). This mechanism may explain the post-

breakup deformation of passive margins during

the Tertiary.

Isostatic uplift accompanies erosion, but it does

not last long before altitudes return to sea level

and erosion ceases, unless other causes of

uplift operate.

Pether Late Tertiary and Early Quaternary

Marine Deposits of the

Namaqualand Coast, Cape

Province: New Perspectives

1986 Recognises deposits at Hondeklip Bay as a seaward-thickening suite of

shallow marine deposits laid down during regression from a transgressive

maximum: a younger unit at ~30 m asl and an overlying older unit at 50

m asl. Attributes these two sequences to early Pleistocene and late

Pliocene, respectively.

Recognition of facies establishes the palaeoposition of sea level and aids

in the interpretation of palaeodepth. At the study area, foreshore deposits

can be 2–3 m thick at water depths between +1.5 and –1.5 m. Upper

shoreface deposits are ~3 m thick at depths between –1.5 and –5 m.

Lower shoreface deposits are ~4 m thick, at depths between –5 and –10

m.

Marine deposition is controlled by the interaction between the rate of sea

level change, the bedrock topography, and sediment supply. Bedrock

topography relative to sea-level controls the range of available

palaeodepths by influencing the degree of exposure of the prograding

coastline to wave energy and the orientation of the palaeoshoreline.

Wave-cut platforms are not observed at Hondeklip Bay. Mid-Tertiary


Provides guidance on interpreting palaeosea

level from palaeodepths of observed facies.

LG


197


Are the

Data Used

in the SSC


fluvial bedrock topography has been exhumed by Neogene

transgressions.

Fossils from the 90 m remnant are remanié fossils, regarded as shelf

fossil lag accumulated on bedrock during more than one sea-level

fluctuation. Therefore, the fossils predate or are contemporaneous with

the enclosing deposit. Mio-Pliocene fossils of the 50 m terrace imply that

it must be Pliocene in age, with the 30 m terrace being Pliocene or

younger.

Pether The Sedimentology, Palaeontolog,

and Stratigraphy of Coastal-Plain

Deposits at Hondeklip Bay,

Namaqualand, South Africa

1994 Provides detailed description of facies observed in excavations at the

Avontuur diamond mine.

No GIS_D0068

_F14_1

LG

Pether et al. Deposits of the West Coast 2000 Reviews the stratigraphy of Cenozoic onland marine formations. No Superseded by Roberts (2006) and Roberts et

al. (2006); however, this paper contains

additional references.

GIS_D0070

_F3_1

LG

Pickford Onland Tertiary Marine Strata in

Southwestern Africa: Local Eustasy,

Local Tectonics and Epeirogenesis

in a Passive Continental Margin

Setting

1988 Reviews the ages of Tertiary marine deposits along the west coast of

South Africa.

No Regional marine terrace correlations GIS_D0069

_F1_Pickfor

d_1998

LG

Ramsay 9000 Years of Sea-Level Change

Along the Southern African Coastline

1995 Tidal range averages 2 m (high microtidal).

Documents several phases of beachrock formation during Pleistocene

and Holocene sea-level fluctuations.

Mid-Holocene highstand remained at the level long enough to wave-

plane and incise potholes into competent aeolianite.

C-14 ages are corrected for variation in isotope fractionation and for the

apparent age of seawater.

No Regional marine terrace correlations KLH

Ramsay &

Cooper

Late Quaternary Sea-Level Change

in South Africa

2002 This paper provides a late Quaternary sea-level curve from the

penultimate interglacial period to the present for South Africa, based on a

range of sea-level indicators in various regions.

No Regional marine terrace correlations

Palaeosea-level indicators:

Spring tidal range +2 m

Barnacles and attached oysters ± 0.5 m

Coastal wetlands ± 5.0 m

Beachrock forms at 0.1 to 0.2 m below MSL at

the freshwater/saline interface (p. 82)

Wood in channel scours ± 0.6 m

GIS_S0034

_F2

KLH

Raymo & Collapse of Polar Ice Sheets During 2012 Modelled the spatial pattern of postglacial crustal subsidence for MIS 11 No Estimate eustatic sea level to ~6–13 m above Figure 1 LG


198


Are the

Data Used

in the SSC


Mitrovica the Stage 11 Interglacial by computing global sea-level variations using a gravitationally self-

consistent theory valid for spherically symmetric, linear viscoelastic earth

models. Near-field of the former MIS 12 ice sheets, postglacial rebound

can result in subsidence of over 100 m over 9 kyr, creating peripheral

bulges with maximum amplitude of +20 m. Therefore, sea-level

highstands will date the end of the interglacial at sites within the

subsiding peripheral bulge, and stillstands far in the far field will date the

beginning of the interglacials.

The predicted highstand for the Bahamas lying on the outer flank of the

peripheral bulge is 7.4 m. Glacial-isostatic adjustments of ~10 accounts

for the high observations (+20 m) at these locations. The eustatic global

sea level for MIS 11 is estimated at ~6–13 m in this study. This analysis

assumes that the melting of the Western Atlantic Ice Sheet and the

Greenland Ice Sheet occurred towards the end of MIS 11.

the present day value in the second half of MIS

11.

provides a

sea level

curve for

MIS 11.

Reddering &

Esterhuysen

Sedimentation in the Gamtoos

Estuary

1984a The Gamtoos inlet migrates eastwards under fair weather conditions, the

opposite direction of the prevailing longshore current. The inlet may be

blocked during conditions of heavy swell. During heavy freshwater floods,

the inlet tends to breach the westernmost part of the barrier.

p. 15—

Beachrock crops out on the western bank of the channel near the inlet

and is overlain by part of the coastal dunefield.

p. 44—

Aerial photos indicate several relict channel generations on the lower

Gamtoos floodplain. The remnant channels seem to have migrated

eastwards during a drop in sea level such that the floodplain is terraced

with older, higher channel remnants on the western floodplain edge.

p. 47—

Wood associated with marine Turritella capensis and oyster shells from 9

m below MSL had an age of 1,170 ± 50 yr BP. Terraces are younger than

this stratigraphically, although this is inconsistent with other field

observations.

Beachrock outcrops to the south of the bridge are exposed at 3 m asl.

Prominent river terraces at 6 and 18 m asl (Davies, 1972).

p. 48—

Inlet migration aided by sedimentation by the coastal dunefield.

p. 61—

No Coastal geology near the Gamtoos Fault.

Eastward migration of Kabeljous inlet may have

created “palaeoshorelines”.

River terraces and beachrock indicate that

regional uplift may dominate over basin

subsidence.

GIS_S0072

_F4.2

Figure 1.1

shows

locations of

abandoned

river

channels

and dunes.

Figure 4.2

shows more

detailed

dunes and

abandoned

channels

over a

smaller

geographic

range than

Figure 1.1.

Figure 4.3

MEMA


199


Are the

Data Used

in the SSC


Dunefield is probably younger than 6 ka. shows

elevations of

abandoned

river

channels.

Reddering &

Esterhuysen

Sedimentation in the Kabeljous

Estuary

1984b p. 4—

The drainage basin lies mostly on a raised coastal marine platform.

p. 10—

The deposits of the estuary overlie Mesozoic conglomerate and sand

stone.

No Information on the ages and elevations of

Quaternary deposits and geomorphic surfaces

can be used to evaluate evidence for

reactivation.

Geology of St Francis Bay

MEMA

Roberts Dating and Preliminary Correlation of

Raised Marine and Estuarine

Terraces on the Western and

Southern Coasts of South Africa,

Final Report

2006 Provides a review of the lithostratigraphic framework for Cenozoic marine

deposits of Southern Africa.

Summarises field observations and dating results for marine deposits

with palaeosea-level indicators.

MIS 11 deposits identified at sites BZ3, Dana1, Dana2, KB1, Coega2,

and Coega4.

Two MIS 11 highstands are observed in the Dana Bay section, with index

points of 5.8 and 1.2 m.

MIS 5e deposits observed at locations SKU12, CHU3, CHU4, ARM2,

ARM3, Dana Bay 2 (Dana5, Dana6, Dana7), GBR2, GBR3, SW1, SW2,

SW3, GT1, NHN2, and NN1.

MIS 5c deposits were dated at Arniston.

An earlier MIS 5e highstand at 0.5 m is observed at Sedgefield.

The 10 most reliable ages for MIS 5e average to 121.09 ka, with an

average elevation of 6 m.

p. 117—

Gamtoos River mouth—Estuarine deposits of fine silty sand with

abundant bioturbation and estuarine fossils such as Solen capensis.

Estuarine deposits overlain by reddish aeolianites. MSA artifacts at +4.2

m amsl suggest a last interglacial age. OSL date gave no reliable age,

possibly due to the very high dose rate (-33.9487, 25.0286).

Maitland River mouth—One of the highest Holocene deposits

encountered in the study, a 5.8 m storm beach. Intact specimen of

Patella sp. Had an age of 6383 BC. Based on calibration with the modern

storm beach, this represents a sea level of ~1.7 m amsl (-34.00766,

25.3387).

Yes

(Indirectly)

Regional marine terrace correlations GIS_T0035

compiles

Tables 2-4

LG


200


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in the SSC


Figure 71—

Gamtoos—Estuarine deposits from 1.5 to 4.1 m asl. MSA artifact from

overlying aeolian sand.

Figure 73—

Maitland—Storm beach deposits overlie a platform cut into the limestone

of the Cape Supergroup.

Roberts & Brink Dating and Correlation of Neogene

Coastal Deposits in the Western

Cape (South Africa): Implications for

Neotectonism

2002 Aeolianites in the Lower Quarry at Propect Hill rest conformably on shelly

upper shoreface to foreshore marine sediments, documenting Plio-

Pleistocene transgression to ~30 m.

Yes

(Indirectly)

Regional Marine Terrace correlations LG/ KLH

Roberts et al. Regional and Global Context of the

Late Cenozoic Langebaanweg

(LBW) Paleontological Site: West

Coast of South Africa

2011 Provides a geologic and palaeontological review of the late Cenozoic

record at the Langebaanweg fossil site in the southwestern Cape.

Deposition of the Elandsfontein Formation was initiated in the Oligo-

Miocene at a sea level well below the present datum by the meandering

palaeo–Berg River as upward-fining successions as sea level rose.

Continued marine transgression caused a general rise in the water table

and the landscape was dominated by wetlands, and later by estuarine

conditions as recorded by the Langeenheid Clayey Sand Member of the

Varswater Formation. Marine regression resulted in sub-aerial

weathering of this member, later truncated by the Middle–Late Miocene

Konings Vlei Gravel member, which was extensively weathered during

the Late Miocene lowstands.

Sea level rose during the Early Pliocene. The beginning of transgression

is indicated by a return to fluvio-estuarine conditions as deposition of the

Langeberg Quartz Sand and the Muishond Fontein Pelletal Phosphorite

Members (MPPM) to an elevation of 30 m, and subsequently to 90 m. At

the Langebaanweg site, the MPPM reaches 50 m in elevation, but rises

to 90 m in the Geelbek Embayment and at Elandsfontein. The best

estimate for the age of the MPPM is ~5.1 Ma, based on fossil

assemblages and the normal polarity determined from palaeomagnetic

samples.

The Varswater Formation was truncated by a subsequent middle

Pliocene highstand of 50 m in the Papkuils and Duinefontein

Embayments to the north and south of Langebaanweg. Based on

correlation with global sea-level curves, the age of the 50 m highstand is

~4.5 Ma.

No Three well-documented Pliocene transgressions

~90 m transgression at 5.1 Ma

50 m transgression at 4.5 Ma

30 m transgression at 3.3 Ma

GIS_D0060

_F1

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201


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in the SSC


The Saldanha Bay dune plume postdates the Pliocene highstand at 3.3–

3 Ma.

Ruddock Cainozoic Sea-Levels and

Diastrophism in a Region Bordering

Algoa Bay

1968 This article maps and interprets the Alexandria Formation and the

underlying planed surface. Three major transgression/regression cycles

are interpreted: (1) Early Tertiary, (2) Mio-Pliocene, and (3) Plio-

Pleistocene. Three episodes of late Cainozoic (Cenozoic) uplift and tilting

(total 33 ft per mile gradient). At least 275 ft (84 m) eustatic sea-level

drop in the Quaternary. Sandstills in sea level (erosional evidence) at 20

(6), 60 (18), 80 (24)-100 (30), 170 (52), 190 (58), 210 (64), 275 (84), 300

(91) or lower, and 350 (106) ft (m).The author interprets 16 river terraces

along the Sundays River. Part of the Alexandria Formation is interpreted

as Quaternary in age.

No MEMA

Van Zyl Landscape Evolution of the Garden

Route Between the Bloukrans River

and Mossel Bay.

1997 This thesis maps coastal geomorphology from the Bloukrans River to

Mossel Bay. The thesis maps post-Gondwana platforms on a 1:50,000

scale. The study uses the chronology of Partridge & Maud (1987) and is

part of a two part study of the southern coast. The other half of the work

is presented by Craig (1997). Underlying geolocgical structure such as

the folds in the Cape Fold Belt and jointing have marked influence on the

landscape development. The interpreted Miocene sea cliff has an

elevation of 260-280 m the same range as the base farther east (Craig,

1997).

Yes Recurrence Gamtoos Fault (8.4.3)

Mapped surfaces identified as portions of the

African Surface are not disturbed by the

Worcester Fault

MEMA/ KLH

Waelbroeck et al. Sea-Level and Deep Water

Temperature Changes Derived from

Benthic Foraminifera Isotopic

Records

2002 Applies regressions established between relative sea level and benthic

foraminifera oxygen isotope ratios to the last four climatic cycles.

No Sea level curve on Figure 4. MEMA

Wang et al. A Re-examination of a Human

Femur Found at the Blind River Site,

East London, South Africa: Its Age,

Morphology, and Breakage Pattern

2008 At Blind River, a human femur was collected from a succession of

estuarine calcarenite and storm beach gravels interpreted as the Salnova

Formation overlain by aeolian deposits. Two samples collected from the

estuarine calcarenite have ages of 118 ka and 119 ka, corresponding to

MIS 5e. This sequence corresponds to a transgressive maximum of 10

m.

No MEMA

Zhang The Evolution of the Gamtoos River

Floodplain, South Africa

1995 There are two relict floodplains in addition to the modern floodplain along

the Gamtoos River. The age of the older floodplain is unknown. The

younger is > 40 ka.

Upstream of the railroad bridge, the valley cuts through mostly Enon

Conglomerate. Downstream of the bridge is more easily eroded Kirkwood

No MEMA


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Formation.

The thesis includes discussion of whether the Gamtoos River is older

than the African Surface.

Near the river is a 200 m asl wave-cut platform that dips at ~1° towards

the coastline. There is also an 80–120 m asl terrace that dips at 4°-5°

towards the coastline. The lower terrace is overlain by ill-sorted, rounded

Table Mountain quartzite.

The author recognises three phases of dune development along the

coast with over 100 m of dune sand in some locations.

The author designates the lower river terrace, Terrace 1, and the higher

terrace, Terrace 2. Terrace 2 is at up to 80–90 m asl and dips at 3°.

Terrace 1 is at up to 20–30 m asl upstream and is found at ~12 m asl

near the coast. Estuarine deposits associated with this terrace were

found at 8.2 m asl. A Donax serra fossil from this terrace had an age of

37,700 ± 1,500 yr BP using radiocarbon dating. The shell was taken from

~7.5 m asl. Donax serra has a range from approximately midshore to –3

m asl. The mollusk assemblage from Terrace 1 is similar to the modern

assemblage near Durban (~5°C warmer water).

Near Mondplaas, another radiocarbon age from this terrace was 41,100

yr BP. Figure 5.5 (p. 79) recreates the shoreline from the time of

formation of Terrace 1.

Three radiocarbon ages from the active floodplain ranged from 2,890 ±

50 yr BP to modern (270 ± 60, 60 ± 50 yr BP).

Offshore Depositional and Erosional Processes and Deposits

Anderson et al. The Generation and Degradation of

Marine Terraces

1999 This paper uses a simple cliff erosion model with a realistic sea-level

history, a rock uplift, and a cliff retreat rule to describe the system in

which older marine terraces are removed through deeper transgression

of a subsequent sea cliff into the landmass. The extent of sea-cliff

incursion depends on the duration of the sea-level highstand, the far-field

wave energy input, and the degree to which bathymetric drag dissipates

wave energy.

The paper also addresses sea cliff decay and incision by streams that

further erode older marine terraces.

No KLH

Birch Nearshore Quaternary

Sedimentation off the South Coast of

South Africa

1979 This progress report discusses nearshore sedimentation from Cape

Town to Port Elizabeth based on 1,771 km of seismic reflection and 574

km of side-scan sonar surveys.

No Nearshore sedimentation in Thyspunt site

vicinity and surrounding region

The Cape Seal—Cape St Francis compartment

GIS_S0040

_F4

GIS_S0040

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A system of relict aeolianite ridges that have been extensively eroded

overlies the sediments of the Wilderness reentrant. The steep shoreward

edge has an elevation of 15 m asl, and the base of the ridge is at –42 m.

The offshore aeolianite ridge has an onshore equivalent (up to 200 m

high), suggesting offshore equivalents have undergone extensive

erosion.

Submerged aeolianites cover the surface of sediment at the mouth of

Tsitsikamma Point and are also associated with onland dune complex.

Relict submerged aeolianites on the surface of the sediment prism

offshore the Wilderness and Tsitsikamma Points were lithified during a

marine regression, possibly during the Eemian or the Tertiary (e.g.,

similar to features off the Natal coast) (p. 140).

Nearshore flat (0.1 degree) continental shelf; seafloor drops rapidly to –

60 to –80 m within 5 km of shore, but deepens only to –120 to –130 m at

the shelf break ~20 to 75 km from shoreline (slope 0.03° to 0.15°).

Alluvial fans during regressions would have formed at

–60 to –80 m isobaths. It would be unlikely that sediment could escape

the nearshore and inner shelf during regressions because of the width

(70 km) and flatness of the shelf and the probable weak-flowing river

systems.

has the least sediment accumulation, with only

minor unconsolidated material observed within a

narrow corridor (5.5–13 km wide). At the

eastern end of this region, sediment is being

blown onshore and transported overland for

some distance before being redeposited in the

nearshore in the St Francis Bay compartment. A

second discrete sediment package within the St

Francis Bay compartment is to the result of

influx of Gamtoos River sediment.

Minor sediment accumulations that occur off

Slang and Thys Bays on otherwise rocky,

sediment-free seafloor are primarily aeolian in

origin.

_F9

GIS_S0040

_F12

Bremner & Day Acoustic Stratigraphy and Late

Cenozoic Sediments in Algoa Bay

1991 This paper describes palaeoriver channels, wave-cut terrace levels, and

aeolianite ridges, and provides a conceptual model that accounts for the

fate of littoral sediment at various sea-level elevations, based on

interpretation of continuous shallow seismic profiling in Algoa Bay.

Two palaeoriver channels, from the Coega and Sundays Rivers, are

traceable across the western part of Algoa Bay and two possible

additional cones, both thought to be associated with the Bushmans River

to the east.

Wave-cut terraces in Algoa Bay were identified from the seafloor

morphology.

No Marine terrace regional compilation

Wave-cut platforms at approx. –70 m (Pl. 7.9)

and –90 m, –116 m, and –135 m (Pl. 7.10). The

deeper platforms at and below –90 m are

overlain by dissected aeolianite remnants.

KLH

Cawthra & Uken Modern Beach Rock Formation in

Durban, KwaZulu-Natal

2012 Beachrock less than 72 years in age is found at roughly mean low water

near Durban. This beachrock formed farther south than most modern

beachrocks and is the youngest known beachrock in South Africa.

No MEMA

Cooper Beachrock Formation in Low

Latitudes: Implications for Coastal

Evolutionary Models

1991 This paper discusses conditions for beachrock formation and possible

limitations of the long-term reduction in sediment volume during the

course of the Pleistocene.

No KLH


204


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In South Africa, the presence of relict beachrock in the southern Cape

(Siesser, 1972; Barwis & Tankard, 1983), probably dating from the last

interglacial, provides evidence that during warmer interglacials, potential

beachrock-forming areas may be extended: beachrock is not forming in

the southern Cape under present climatic conditions.

Beachrock forms by the carbonate cementation of sand grains on

beaches and is more or less contemporaneous with deposition.

The presence of several semicontinuous cemented beachrock and

aeolianite zones, both on the South African shelf (Martin & Flemming,

1988; Ramsay & Mason, 1990a, 1990b) and onshore (Hobday, 1976;

Cooper & Flores, 1991), indicates that several phases of beachrock

formation have occurred during the Pleistocene.

Cooper & Flores Shoreline Deposits and Diagenesis

Resulting from Two Late Pleistocene

Highstands near +5 and +6 Metres,

Durban, South Africa

1991 Beach, dune, and swash deposits are interpreted to be of late

Pleistocene age.

No MEMA

De Decker The Sediments of Plettenberg Bay

and the Submerged Robberg Spit

1983 The submerged spit off of Robberg formed during the Flandrian

Transgression and evidence such as grain-size trends suggests it is

actively building out towards the east due to littoral drift.

No MEMA

De Decker The Geological Setting of

Diamondiferous Deposits on the

Inner Shelf Between the Orange

River and Wreck Point,

Namaqualand

1986 This study examined the shelf geology from the Orange River mouth to

Wreck Point. The inner shelf dips at 1–2 degrees. A mud belt is present

from 50 m to 70 m depth. Megaripples parallel to shore formed by either

rip currents or wave activity.

Submerged terraces at –45 to –40 m; –30 m; –22 to –25 m; –18 to

–20 m; –14 to –16 m; and –10 m.

No MEMA

Dingle The Anatomy of a Large Submarine

Slump on a Sheared Continental

Margin (SE Africa)

1977 The submarine Agulhas Slump is described from bathymetric and

continuous seismic reflection records.

No MEMA

Du Plessis &

Glass

Geology of the Sea Floor in the

Vicinity of Jahleel and St. Croix

Islands, Algoa Bay

1991 Geology was investigated using side-scan sonographs, seismic-reflection

profiles, and sea-bed samples. Mesozoic strata is overlain by 0–14 m of

partly lithified late Pleistocene material, which, in turn, is overlain by a

discontinuous cover of Flandrian to Recent unlithified sediment, generally

less than 1 m thick. Several discrete units are identified:

The oldest is a conglomeritic lag.

The next two oldest units may be remnants of partly shoreface and partly

aeolian deposits. They are believed to have been deposited as sea level

No Marine terrace regional compilation

Sea-level stillstands in Algoa Bay at –15 m, –23

m, and –20 m (possibly during the Wurm

interglacial period, 30–60 ka).

KLH


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dropped to –15 m, and then remained constant at –23 m for a short time

during a general regression.

The youngest lithified material was deposited as the sea transgressed

the area, possibly during the Wurm interstadial (30–60 ka). The bulk of

the material eroded during the Flandrian transgression is believed to

have been moved onshore and deposited as dunes.

Etienne et al. The Use of Boulders for

Characterising Past Tsunamis:

Lessons from the 2004 Indian Ocean

and 2009 South Pacific Tsunamis

2011 Discusses characteristics of boulder deposits associated with historical

tsunamis, and criteria for differentiating tsunami-transported boulders

from storm deposits. Boulder distribution, preferential orientation, and

numerical simulation of boulder transport are discussed. A comparison of

boulders from the South Pacific and Indian Ocean tsunamis shows

similar characteristics, such as limited landward extent and the absence

of landward fining.

p. 81—

Boulder beaches are observed in high-energy environments of rocky

coasts dominated by storm conditions. Boulder ridges and boulder

beaches probably indicate organisation of coarse clasts into ridges by

repeated reworking by many waves rather than the impact of only a few

waves, as occurs during a tsunami.

No Pertinent to the geological investigations

(marine terrace mapping project)—boulder

beaches at Cape St Francis.

Tsunami deposits—criteria

-- KLH

Flemming Underwater Observations Along a

High-Energy, Cliffed Coastline

(Tsitsikama)

1974 This study looked at nearshore sedimentation along the Tsitsikama cliffs.

Bedrock exposed is the Gamtoos Group Klein River Formation and the

Cape Supergroup Peninsula Formation. There are also large, wave-

generated bedforms made of gravel and coarse sand. Fines have likely

been winnowed by wave activity. The sand sheet seasonally migrates

closer to shore in the summer.

No MEMA

Flemming Underwater Sand Dunes Along the

Southeast African Continental

Margin—Observations and

Implications

1976 Underwater sand dunes are generated by the Agulhas Current between

Durban and Port Elizabeth. The dunes occur at water depths greater than

50 m, are up to 8 m wide, with wavelengths up to 250 m. The near-

bottom velocities reach ~1.3 m/s.

No MEMA

Flemming et al. Onshore and Offshore Coastal

Aeolianites Between Mossel Bay and

Knysna

1983 Coastal aeolianites onshore and offshore of Mossel Bay and Knysna are

mapped. Submerged aeolianite ridges are up to 50 m thick and are found

to a depth of 70 m. Submerged dunes, including dune crests, are overlain

with scattered pebbles, indicating they were once coated with fluvial

sediment.

No MEMA

Flemming & Hay Sediment Distribution and Dynamics

on the Natal Continental Shelf

1988 This chapter examines the influence of the Agulhas Current on

bathymetric morphology.

No


206


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Fugro Survey

Africa (Pty) Ltd

Geophysical Survey Report for

Thyspunt Eskom Site Surveys South

Africa

2007 Summarises the collection and and interprets a marine geophysical

survey of the Thyspunt site area (8 km radius), including single and

multibeam hydrographic echo sounder, side-scan sonar, Pinger sub-

bottom profiler, and magnetometer data acquisition.

Faults and slump features are interpreted from these data in the offshore

site area, but no information as to when they were last active was

obtained.

No Structural features

Fracture orientations 40°/220° and ~50°/230°

Small faults trending NE-SW are mapped in

both the western and eastern blocks of

sandstone outcrop at the sea bed. Maximum

lateral displacement of up to 250 m.


KLH

Green Sediment Dynamics on the Narrow,

Canyon-Incised and Current-Swept

Shelf of the Northern KwaZulu-Natal

Continental Shelf, South Africa

2009 This study uses side-scan sonar, multibeam bathymetry, and sub-bottom

data to examine the interaction of strong boundary currents and

submarine canyon bathymetry.

No MEMA

Green & Uken First Observations of Sea Level

Indicators Related to Glacial Maxima

at Sodwana Bay, Northern KwaZulu-

Natal

2005 In a study of the shelf on the east coast of South Africa, the authors

found evidence for three submerged shorelines at –106 m, –124 m, and

–130 m. Evidence for the –124 m shoreline is caves and a relict cobble

beach. These shorelines are evidence of tectonic stability.

No MEMA

Hagedorn Silcretes in the Western Little Karoo

and Their Relation to

Geomorphology and Paleoecology

1988 Silcretes up to 10 m thick have ages of 7.3 Ma and 9.4 Ma. Yes Kango Fault (8.4.1) Recurrence

Provides age information for datums used to

evaluate long term slip rate.

KLH

Horwood Thyspunt 8 km Radius Marine

Survey: Structural Geology Report

2009 Provides a discussion of structural features interpreted from seismic data

collected in November 2006 by Fugro Survey Africa (2007) for Eskom.

Side-scan sonar and Pinger paper records were not available to the

author for his review.

No

(SSC)

Yes

(input to

surface

faulting

hazard at

the site)

Offshore structural features in the Thyspunt site

area (8 km radius)

NW/WNW fractures subparallel bedding trend.

At least one of these fractures is interpreted to

be a fault, which may intersect the shoreline

outside the area of exposed outcrop at

Klippepunt.

A series of small, pervasive NE-trending faults

displace the WNW-trending faults and are

therefore interpreted to be younger.

No evidence of recent faulting.

Evidence for offshore slump

Sedimentary features, which were interpreted

by Fugro Survey Africa (2007), are most likely

erosion channels, but additional analysis is

needed to confirm this hypothesis.

KLH

Martin &

Flemming

Holocene Shelf Sediment Wedge off

the South and East Coast of South

1986 This paper discusses the characteristics of continental shelf sediments

on the eastern and southern coasts of South Africa based on

No Morphology of the coastal region

p. 28

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Africa interpretation of seismic reflection survey and side-scan sonography

data, box-coring, and grab-sampling. Holocene sediments form an inner

shelf sediment wedge, between 2 and 40 km wide, extending quasi-

continuously over 1,300 km. The wedge lies unconformably on an incised

erosion surface truncating folded and faulted Palaeozoic and Mesozoic

strata.

Morphology of continental shelf in Thyspunt site

region. The south coast is wide (maximum 270

km near Point Agulhas), dominated by

southwesterly swells, and features several

headlands and associated bays.

Submerged palaeoshoreline features

p. 30

The pre-Quaternary rock-head descends

steeply seawards from coastal cliffs and flattens

at water depths of about 80–100 m where

Mesozoic strata have been truncated by

repeated transgressions and regressions.

Multiple parallel aeolianite ridges on the south

coast extend from the shelf onshore. Seismic

data show the bases of these cordons, which

suggest sea-level stillstands at 40, 50–55, 65–

70, and 85–90 m depth, in general accordance

with knickpoints observed in bedrock.

Submerged depositional units

p. 34

On the south coast, Holocene wedge sediments

are thickest just east of two headlands, reaching

20 m off Mossel Bay and 54 m off Cape Seal.

p. 39

A prograding sediment body is accumulating on

the shelf, at water depths of between 40 and 90

m—the Robberg submerged spit bar.

p. 41

Submerged spit bars are also associated with

Cape Infanta and Cape St Francis. Submerged

spit depocenters are attached to the shoreline

but prograde in water depths of between 20 and

90 m. Their depth of formation is controlled by a

balance between sediment supply and

prevailing energy levels.

Martin & Aeolianites of the South African 1987 Two phases of aeolianite deposition between Mozambique and the No MEMA


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Flemming Coastal Zone and Continental Shelf

as Sea-Level Indicators

southwestern Cape: Pliocene and late Pleistocene. This study explored

both on- and offshore aeolian deposits. Notable submarine shorelines at

40 m, 50–55,m, and 65–75 m. In some locations the ridges are covered

by the Holocene sedimentary wedge.

Martin &

Flemming

Physiography, Structure, and

Geological Evolution of the Natal

Continental Shelf

1988 This paper provides a description of the physiography, stratigraphy, deep

and shallow structure, shelf-edge slumps, canyons, prograding

sequences, and factors influencing shelf evolution.

No Generally, the information is too specific to the

Natal region to be useful for the Thyspunt

SSHAC PSHA. However, there is some

information on the water depths of submerged

aeolianites that may be incorporated into the

regional palaeosea-level database.

Figure 2.14

Location and depth of submerged aeolianite

ridges (depth of the base of the cordon is

inferred to represent palaeosea level).

GIS_S0033

_F2.14

MEMA

Steward & Smith Geophysical Survey Report for

Thyspunt Inshore Site Survey for

Eskom, South Africa, Survey Period:

28 May to 25 June 2007

2007 Report presents results of an inshore marine geophysical survey that was

conducted by Fugro off the Thyspunt site on behalf of Eskom. The

purpose of acquiring the data was to identify any parameters that would

eliminate the Thyspunt site as being suitable for the construction of a

nuclear power plant. The inshore survey covered two separate blocks,

identified by the Council for Geosciience personnel in an attempt to find

evidence of the Cape St Francis Fault.

The Cape St Francis Fault was not identified in either the West or East

survey blocks, but additional studies (further sub-bottom data and

magnetometer data) recommended to aid in locating the fault.

No Cape St Francis Fault- assessment of location

and Seismoenicity

KLH

Uenzelmann-

Neben & Huhn

Sedimentary Deposits on the

Southern South African Continental

Margin: Slumping Versus Non-

deposition or Erosion by Oceanic

Currents?

2009 Interpretation of seismic profiles extending from the southern South

African shelf into the deep sea reveal a strong erosional activity, which

affects large parts of the continental margin. In places, the complete

sedimentary column appears to have been eroded. Previously interpreted

mass movements (e.g., most of the Agulhas Slump) are interpreted as

erosional features, not slumps.

Structures indicating slumping can be identified in only a few places. The

erosional activity is confined to specific water depths that are suggested

to correlate with the Agulhas Current, Antarctic Intermediate Water, North

Atlantic Deep Water, and Antarctic Bottom Water. A stable circulation

pattern comparable to that of the present day is interpreted to have

existed since the Neogene.

Yes Characterisation of the Agulhas Fracture Zone

(AFZ) fault source (8.4.2)

The Cenozoic sedimentary column generally is

very thin, showing a maximum thickness of

1,400 m. This leads to extremely low mean

sedimentation rates.

Erosion of Oligocene to Holocene sediments,

and in places, the complete sedimentary

column, was observed in specific water depth

intervals. Evidence for mass movements such

as the Agulhas Slump can be identified in only a

few locations. Nondeposition and erosion thus

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appear to have been the major processes

shaping the sedimentary units.

Erosion is inferred to be an ongoing process

since the erosional features are neither filled nor

levelled out.

The removal of surficial to Oligocene

sedimentary layers suggests that the presently

observed circulation have been stable since the

Neogene.

Uenzelmann-

Neben et al.

Palaeoceanographic Interpretation of

a Seismic Profile from the Southern

Mozambique Ridge

2011 Seismic reflection data from the southern Mozambique Ridge show

indications for a modification in the oceanic circulation system during the

Neogene. Major reorganisations in the Indian Ocean circulation system

accompanying the closure of the Indonesian Gateway led to the onset of

current-controlled sedimentation in the vicinity of the Mozambique Ridge

at ~14 Ma. The modifications in water mass properties and path are

documented in changes in seismic reflection characteristics in the

Mozambique Ridge area.

Correlating these with identified changes of the Nd isotope evolution in

deep water masses, the general present-day large-scale circulation in the

southern Indian Ocean is suggested to have prevailed for the last 9 Ma.

No MEMA

Woodborne The Geology of the Diamondiferous

Inner Shelf off Namaqualand

Between Stompneus Bay and White

Point Just North of the Buffels River

1987 This study examined the inner shelf at the Buffels River, Namaqualand.

Wave-abraded terraces were found at depths of –14 to –18 m, –22 to –

28 m, –33 to –40 m, and –44 to –53 m depth. The study concluded the

postglacial transgression eroded and redistributed dune sand. On the

shelf, storm waves can transport sand to 30 m depth and cobbles to 15 m

depth.

No MEMA



210

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222

Table 3.7. Data Summary Table - Regional Structures, Thyspunr PSHA.


Is The Data

Used in the

SSC Model?

(Yes, No) Discussion of Potential Data Use GIS Code Originator

Bedrock Structural Analyses

Anderson Estimating Seismicity from

Geological Structures for Seismic

Risk Studies

1979 Uses slip rates and strain rates to estimate seismic moment. Yes Namaqua Source Zone fault geometry

(8.3.5)


Geochronology, South African

Fault Corridor Investigation

2012a Estimates rock uplift rates inferred from cosmogenic nuclide analysis of stream

sediments and concludes that there is no measurable differential uplift in the

southern African field area.

Yes Seismogenic probability and recurrence

Worcester Fault (8.4.5)

MEMA

Bird et al. Plate Tectonics and Earthquake

Potential of Spreading Ridges and

Ocean Transform Faults

2002 Separates the Harvard CMT catalog into spreading and transform earthquakes

along ocean ridges.


Mmax

M 7+ earthquakes on ocean transform

faults

MEMA/

KLH

Boettcher &

McGuire

Scaling Relations for Seismic

Cycles on Mid-Ocean Ridge

Transform Faults

2009 Develops a scaling relation for magnitudes of earthquakes on mid-ocean ridge

transforms.


Magnitudes of largest events (6 < Mw <

7)

MEMA/

KLH

Booth & Shone Folding and Thrusting of the Table

Mountain Group at Port Elizabeth,

Eastern Cape, Republic of South

Africa

1992a Selected outcrops along the Baakens Valley and coastal strip east of Sardinia

Bay were used to determine the overall structure of the Table Mountain Group

(TMG) close to Port Elizabeth. A large recumbent fold structure is interpreted

to be the result of an early phase of shortening. Pelitic horizons were

subsequently smeared out along thrusts in the TMG. This caused repeated

stacking, resulting in an unusually thick sequence of quartzites. The last phase

of tectonism was extensional. An 8 km broad graben formed between two

prominent W-NW-striking fault zones: the Chelsea-Noordhoek and Moregrove

Faults.

No

RC

Booth & Shone The Pre-Cape–Table Mountain

Group Contact West of Port

Elizabeth

1992b Discusses an alternative interpretation to Bell (1980) for the thickness of the

Table Mountain Group (TMG) quartzites near Port Elizabeth. The author

discusses that the reason for the unusually thick sequence is explained by the

presence of upside-down TMG strata, and the previously unrecognised

Chelsea-Noordhoek and Moregrove thrust faults.

There is a brief mention of inversion on these structures during the breakup of

Gondwana.

The contact between the TMG and pre-Cape rocks west of Port Elizabeth is

placed at Laurie’s Bay. Although all rocks are deformed, strata of the TMG can

be distinguished from those of the pre-Cape by the occurrence in the TMG of

bedding, cross-bedding, ripples, and trace fossils. A north-striking fault, the

Laurie’s Bay Fault, separates the TMG from pre-Cape rocks. A combined right-

Yes Mesozoic extension (8.4.3) and

reactivated thrusts by normal faulting

(8.3.1, 8.4.1, 8.4.3, and 8.4.4).

RC/MEMA/KLH


223


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SSC Model?


lateral, strike-slip, and dip-slip movement along the fault, under ductile

conditions, downdropped TMG strata to the east. Earlier structures, including

cleavages, folds, and a lineation, were reoriented in the fault zone, showing

that the contact between TMG and pre-Cape rocks is a tectonic one. Previous

workers did not recognise the fault contact at Laurie’s Bay.

Bufe Stress Distribution Along the

Fairweather–Queen Charlotte

Transform Fault System

2005 Models the stress distribution along the Fairweather–Queen Charlotte

Transform by examining some of the historical earthquakes in the fault system.


M 8.1 Queen Charlotte Island

earthquake

MEMA/

KLH

Clark et al. Australia’s Seismogenic

Neotectonic Record: A Case for

Heterogeneous Intraplate

Deformation

2011 Divides the Australian continent into six seismicity source zones, based on

palaeoseismological studies, and compares the fault recurrence and

behavioural characteristics of each.

Kango Fault (8.4.1)



MEMA/

KLH

Cole & Naudé Final Report: Airborne Survey of

Thyspunt, Report No. 2007-0006

2007 Airborn magnetic surveys were conducted over the Thyspunt site to look for

faults. The Cedarberg and Gydo Formations are responsible for prominent

NW-SE-striking anomalies. Several linear features were interpreted as possible

faults.


MEMA

Collettini & Sibson Normal Faults, Normal Friction? 2001 Compiles the dips from focal mechanisms of shallow, intracontinental, normal-

slip earthquakes.



MEMA/

KLH

Crone et al. Episodic Nature of Earthquake

Activity in Stable Continental

Regions Revealed by

Paleoseismicity Studies of

Australian and North American

Quaternary Faults

1997 In stable continental regions, faults show episodes of activity separated by

quiescent intervals of at least 10,000 yr, and, commonly, 1,000,000 yr or more.

This study looked at Australian faults with historical surface faulting events

(1986 Marryat Creek and 1988 Tennant Creek), as well as the Meers and

Cheraw Faults in the United States.



MEMA/

KLH

Crone et al. Paleoseismicity of Two

Historically Quiescent Faults in

Australia: Implications for Fault

Behavior in Stable Continental

Regions

2003 Examines the rupture history of the Roopena and Hyden Faults in South

Australia. Both faults are in areas of limited to no seismicity but have evidence

of multiple surface-faulting events in the Quaternary.



MEMA/

KLH

EPRI et al. Central and Eastern United States

Seismic Source Characterization

for Nuclear Facilities

2012 Examines the recurrence interval and evidence for temporal clustering for nine

faults in the Central and Eastern United States. The faults studied are the

Charlevoix, Charleston, Cheraw, Meers, and Wabash Valley, as well as four

faults within the Reelfoot Rift zone—the New Madrid Fault System, the Eastern

Rift Margin Fault, the Marianna Fault, and the Commerce Fault Zone.


Recurrence/Recency

MEMA/

KLH

Goedhart &

Hattingh

The Geology of the Coega River

Mouth and Proposed Adjacent

1997 Coega Fault—Post-Miocene ML5.8-6.2 earthquake on the Coega Fault (0.5–1

m offset), may be Pleistocene in age.

No MEMA


224


Is The Data

Used in the

SSC Model?


Industrial Development Zone,

Eastern Cape

Cross section across Coega Fault shows no deformation in the Alexandria

Formation (Fig. 4.3).

Hälbich Disharmonic Folding, Detachment

and Thrusting in the Cape Fold

Belt

1983 Links disharmonic folding and northward-directed overthrusting in the Cape

Fold Belt to decoupling in the Nardouw Shale and Cedarberg Shale. Thin-

skinned tectonics and sole thrusting occur in the eastern, more intensely

deformed parts of the fold belt.


MEMA

Hälbich The Cape Fold Belt Orogeny:

State of the Art 1970s–1980s

1992 Summarises publications on the history of the Cape Fold Belt and the state of

scientific understanding of its formation. The Cape Fold Belt was deformed in

four episodes: 278 Ma, 258 Ma, 247 Ma, and 230 Ma.


MEMA

Hanson et al. Style and Rate of Quaternary

Deformation of the Hosgri Fault

Zone, Offshore South-Central

Coastal California

2004 For a 70-degree or steeper-dipping fault, a H:V ratio of approximately 1:8 or

greater would suggest that the fault is a strike-slip fault.

Yes Style of faulting Agulhas Fracture Zone

(8.4.2)

MEMA/

KLH


Investigations—Kango Fault

Study

2012b This report details palaeosesmological studies along the Kango Fault.

The 92–101 km long eastern segment of the Kango Fault west of De Rust

appears to be unique among faults within the Ceres-Kango-Baviaanskoof-

Coega fault system in that it shows evidence for repeated surface-faulting

events during the Quaternary.

Palaeoseismic investigations at the M1.26 site document evidence for two

latest Pleistocene to Holocene surface-faulting events. The timing of the

penultimate event (PE) and most recent event (MRE) at this site is constrained

by C14 and OSL ages to be between 15 ka and 10 ka (most likely between 13

kyr BP and 10.3 kyr BP [referenced to AD 1950] and 4.5 ± 0.4 kyr BP).

Additional dating of samples previously collected from the M1.42 trench,

combined with re-evaluation of photodocumentation of the excavation wall at

the M1.42 site, suggests that these two events also are recorded in the

statigraphic and structural relationships observed in the M1.42 trench. The

constraints on timing from the M1.42 trench suggest that the PE occurred

between 12 yr BP and 10.9 yr BP, and the MRE event occurred 6 ± 0.5 kyr BP.

This interpretation conflicts with the previous conclusion that the M1.42 trench

recorded a single surface-rupturing event approximately 10 ka.

The youngest faulting at the M1.133 site in the eastern section of the

reactivated Kango Fault appears to have occurred between 22.6 ka and 25.4

ka. This estimated age is based on CN analysis of a series of samples taken

from the scarp face at this site.

The length, segmentation, and geometry of the Quaternary-active Kango Fault

Yes Kango Fault (8.4.1) Seismogenic

probability, Mmax, Geometry,

Recurrence (timing and slip rate)

Analogy for Worcester Fault (8.4.5)

Seismogenic probability and magnitude

KLH


225


Is The Data

Used in the

SSC Model?


are largely inherited from structures initially formed during the Permo-Triassic

Cape Orogeny that were reactivated during the breakup of Gondwana in the

Mesozoic and subsequent rifting of the South Atlantic.

Remapped active trace using DEM, aerial photographs, and GoogleEarth

images.

Temporal clustering—The two most recent surface-rupturing events at the

M1.26 and M1.42 sites were preceded by a long period of several tens of

thousands of years of no activity (at least 63–123 kyr or longer).

Long-term slip rate—A long-term vertical displacement and slip rate were

measured across the western part of the Quaternary-reactivated Kango Fault

at the M1.42 site. Cumulative net vertical separation of erosional surfaces

(pediment or strath terraces) formed on top of bedrock in the hanging wall and

footwall of the fault zone at this site ranges from 26 m to as much as 33.4 m.

CN burial ages of clasts within alluvium overlying the erosional surfaces range

from 0.6 Ma to 3.2 Ma, with short (19–121 kyr) periods of initial exposure

before burial. Within the resolution of the CN burial dating method, the burial

ages for the gravel deposits directly overlying the erosional surface on the

hanging wall (2.2–3.2 Ma) cannot be differentiated from the burial age of the

basal gravel from the footwall (2.1 Ma). Using an age estimate of 2.5 ± 0.6 Ma

for the displaced basal gravel unit, and a net vertical separation of 26–33.4 m

yields a long-term vertical slip rate ranging from 0.008 mm/yr to 0.018 mm/yr

for the Kango Fault at the M1.42 site.

Long-term slip rate—Cumulative net vertical separation of the erosional

surface of the Tertiary gravel (Tg) pediment remnants that are displaced by the

Kango Fault in the easternmost reach of the reactivated fault (at the M1.30 and

M1.33 sites) ranges from 5 m to 9 m. The long-term cumulative slip on the fault

at the eastern end appears to be less than what is observed at the M1.42 site

(26–33.4 m) from interpretation of boring data, or at the M1.35 site (minimum

of 11.4 ± 4 m, inferred offset across younger and older scarps in Tg surface).

Estimated long-term vertical slip rates at the M1.133 site range from a value of

0.012–0.025 mm/yr (based on the assumption that the 10Be exposure age

[0.36–0.38 Myr] for the boulders represents a minimum limiting age of the Tg

surface that is displaced 7 ± 2 m across the entire fault zone), to a lower value

of 0.001–0.01 mm/yr (based on the assumption that the Tg surface records

cumulative slip over a longer period of 1–4 Ma).

At the M1.133 site, strata within the Tg deposits may be offset by an amount


226


Is The Data

Used in the

SSC Model?


similar to that of the surface offset on the main fault in the youngest zone of

faulting. CN analysis of one of the six clasts that were collected from within a

fissure near the fault scarp, where it presumably was shielded from cosmic

rays by several metres of silcrete, suggests that the Tg clast was deposited

many 10Be half-lives ago (10Be half-life ~1.4 Myr); this age is consistent with

the estimated age (7–9 Ma) of Tg silcrete in the Oudtshoorn basin.

Assuming that the cumulative slip postdates the formation of caprock across

the entire fault zone, the long-term slip rate at the M1.133 site would be as low

as 0.0007–0.001 mm/yr (7 ± 2 m/7–9 Ma, based on electron spin resonance

ages for Tg silcrete in the Oudtshoorn basin).

Alternative rupture scenarios are considered in estimating the maximum

magnitude of expected ruptures for the Kango Fault, as follows: 30 km (the

length of the western reach of the Kango Fault with clear evidence of two latest

Pleistocene to Holocene surface ruptures); 50 km (the length of the western

part of the reactivated fault zone from the endpoint near De Rust to

Toorwaterpoort gorge that shows geomorphic evidence for a possible

continuous Holocene scarp); and 92 km (the length of the fault with evidence of

Quaternary surface faulting).

Average displacement per event for the two most recent surface-faulting

events is best constrained at the M1.26 and M1.42 trench sites. Evidence for

cumulative net vertical separation of 2–3 m from two events at these sites

suggests an average vertical displacement of 1–1.5 m per event. Net tectonic

slip per event based on an assumed fault dip of 45°–70° at depth would be 1–2

m.

Empirical relationships relating moment magnitude (M) to rupture

characteristics (i.e., rupture length, rupture area, and average displacement)

that have been developed from data specific to stable continental regions, as

well as more active regions, were used to estimate the maximum magnitude of

palaeoearthquakes that have occurred on the Kango Fault. The estimated

magnitudes range from approximately M 6.6 to M 7.6; values in the range of

M 7.0 to M 7.4 are preferred estimates based on rupture areas defined by

seismogenic depths of 15–17 km and average displacement-per-event data.

Hill Quaternary Faulting in the South-

Eastern Cape Province

1988 Abstract—

No direct evidence for post-Tertiary faulting on a transverse fault at the Paul

Sauer Dam (now the Kouga Dam). There are indications that the displacement

could have taken place under conditions of confining pressure, which in all

Yes Lack of evidence for recent activity on

“Paul Sauer” Fault.

Recency—Quaternary activity on the

RC/MEMA/KLH


227


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Used in the

SSC Model?


probability would have preceded (late) Cenozoic uplift and denudation.

Paul Sauer Fault

p. 401—

“Paul Sauer” Fault described as post-Tertiary dip fault by Pike (1968).

Displacement took place along several steeply inclined planes in a zone 30–50

m wide. Within this zone, the rock (quartzite) is highly brecciated and

recemented by silica. Maximum downthrow is estimated to be on the order of a

few hundred metres to the east. Because no irrefutable evidence for post-

Tertiary displacement could be found, it is thought that the presence of ductile

failure, as indicated by systems of bifurcating fracture planes (e.g.,

Jaroszewski, 1984), points to the displacement having taken place mainly

under confining pressure. In this case, that would probably have predated

(late) Cenozoic uplift and erosion.

Kango Fault

Article describes late Quaternary reactivation of the Kango-Baviaanskloof fault

system.

Scarp height does not exceed 5 m.

Attributes alluvial fans that cross the fault as the result of episodic heavy

downpours. Suggests an age of Quaternary, or possibly during the late

Pleistocene hypothermal with its increased precipitation.

~100 km. The length for the reactivation is also described as “confined to the

De Rust–Antoniesber segment of the fault”, which is ~50 km long. (p. 401)

En echelon scarps observed across high terrace at the farm Annex Misgaad 18

(Fig. 6) are suggestive of shear deformation (left-lateral); however, due to the

restricted occurrence of this phenomenon, an alternative explanation may be

that the incoherent and inhomogeneous cover material may be responsible for

differential transmission of youngest fault displacement.

Kango Fault (8.4.1)

5 m scarp along the Kango Fault (8.4.1)

Hiller & Snowden Structural and Stratigraphical

Relationships in the Cape Fold

Belt South of Steytlerville

1983 The role played by gravity in the deformation of the Cape Fold Belt of South

Africa has been the subject of much discussion, with several workers

suggesting that at least some of the deformation was gravity induced. These

suggestions stem from the existence of zones of tight, angular northward-

verging second-order folds progressively stepped down to the north in the

Table Mountain Group of the Cape Supergroup. An investigation of one such

zone of folding in the east-central part of the fold belt reveals a picture of

second-order folds, with wave lengths of about 10–30 m, on the steep northern

limb of a first-order antiform. Second-order antiforms are upward facing, and

No RC


228


Is The Data

Used in the

SSC Model?


second-order enveloping surfaces dip north at about 50 degrees.

During the same episode of deformation that led to this folding, the Table

Mountain Group was thrust northwards about 4–5 km on south-dipping thrust

planes to overlie, in places, the younger Bokkeveld Group. The sequence of

events in the area of study appears to have been as follows:

Formation of small, angular second-order folds verging north.

Development of first-order mega-antiforms and synforms.

Thrusting occurring during the formation of the first-order folds.

All deformation was caused by compression directed from the south, and

gravity played no part in the folding, although it may have played some part in

the thrusting.

Ingram The Coega Fault and Table

Mountain Group Rocks,

Northwest of Uitenhage

1994 A detailed structural analysis of the Peninsula Formation strata (Table

Mountain Group) north of the E-W-striking Coega Fault (Late Jurassic) and 3.7

km NW of Uitenhage shows that thrust faulting is the dominant structural

feature. Steep foreland-vergent thrust faults predominate over shallow

backthrusts. South-vergent folds directly north of the Coega Fault plunging

east and west at shallow angles may have formed as a result of displacement

along large foreland thrust faults or rotation about an axis along the Coega

Fault.

Fold styles vary between open and gentle. N-S compression folds with axial

planes dipping steeply north close to the Coega Fault are refolded by gentle E-

W folds. Reverse faults trend in the same direction as axial-plane trends of

folds. A steep south-dipping transverse cleavage is associated with the

northern limbs of south-vergent folds. Normal faults denote the last stage of

deformation.

On microscale, a mimetic cleavage parallel to bedding is delineated by chlorite

porphyroblasts. A new cleavage S2 occurs at a steep angle to the first local

cleavage S1. White mica crystallised in cleavage seams and quartz in

microlithons by solution and recrystallisation parallel to the first cleavage.

Microfaults and extension fractures are associated with the last phase of

deformation.

No Origin of Coega Fault system RC

Ishii et al. Mw 8.6 Sumatran Earthquake of

11 April 2012: Rare Seaward

Expression of Oblique Subduction

2013 Discusses the tectonic setting of the 2012 M 8.6 Sumatran earthquake as

related to oblique subduction.


Mmax

2012 M 8.6 Sumatran earthquake (not

considered to be a good analogue for

the AFZ)

MEMA/

KLH


229


Is The Data

Used in the

SSC Model?


Jackson & White Normal Faulting in the Upper

Continental Crust: Observations

from Regions of Active Extension

1989 Looks at earthquake foci of large, normal-faulting events and concludes that

the dip range is between 30° and 60°.


Fault Geometry


MEMA/

KLH

Lamontagne Significant Canadian Earthquakes

of the Period 1600-2006

2008 This study catalogs large, historical Canadian earthquakes, including the 1946

M 8.1 Queen Charlotte Islands earthquake.


Mmax

M 8.1 Queen Charlotte Island

earthquake

MEMA/

KLH

Le Roux Structural Evolution of the Kango

Group

1983 Examines the structures and the structural history of the Kango Group.

Author notes that the Kango Fault in general is the contact between the Enon

Formation on the south side and the Kango Group on the north. A note about a

Tertiary surface overlying the fault and having a faint trace visible on aerial

photos suggests post-Tertiary offset.

Post-Tertiary faulting on the Kango Fault.


probability and recency

KLH

Leonard Earthquake Fault Scaling: Self-

Consistent Relating of Rupture

Length, Width, Average

Displacement, and Moment

Release

2010 Proposes self-consistent scaling relations between seismic moment, rupture

area, length, width, and average displacement on a fault.



MEMA/

KLH

Lindeque et al. Deep Crustal Seismic Reflection

Experiment Across the Southern

Karoo Basin, South Africa

2007 Seismogenic thickness of the Kango Fault is >10 km. Yes Kango Fault (8.4.1)


KLH

McCalpin Field Reconnaissance and

Seismic Source Characterization

of the Kouga, “Paul Sauer”,

Kango, and Baviaanskloof Fault

Zones, Cape Fold Belt, Republic

of South Africa

2009a Report summarises the findings of a three-week field reconnaissance in the

Eastern Cape Fold Belt to assess evidence for Neogene reactivation on

several faults, including the Kango Fault.

Notes late Pleistocene to Holocene activity on the Kango Fault.

Author identifies a single-event recent fault scarp in Quaternary deposits (1.5–

2 m) and larger fault scarps (5.2–11.7 m) on Tertiary surfaces. Uses the single-

event scarp to estimate four to nine post-Miocene surface ruptures to yield a

long-term recurrence interval slip rate.

Uncertainty is affected by the age of the Tertiary surface and the time span

during which the ruptures occurred. Due to these uncertainties, the author

recommends simplified probability density functions for most of the seismic

source characterisation.

Estimated the age of site M1.50 displaced fan.

Six sites were visited along the Kango Fault where topographic profiles were

measured across the fault zone to estimate cumulative net vertical separation


Seismogenic probability, Recurrence

and slip rate, Mmax, Rupture geometry

KLH


230


Is The Data

Used in the

SSC Model?


(throw).

At site M1.50, the displaced fan (~1.5 m net vertical separation) is estimated to

be ~100 ka.

At site M1.35, an old and a young scarp are separated spatially by 500 m; the

young scarp is to the south.

Site M1.33 has an old and a young scarp; the young scarp is south of the old

one.

The author concludes that the total length of the fault (~80 km) is too long to

correlate with the measured “single-event” displacements. Rather, the surface

rupture lengths predicted from field measurements suggest shorter rupture

lengths that roughly agree with the segment lengths of the western (45 km)

and eastern (35 km) segments. The author supports this by citing Goedhart

(2006), who infers the ages of the most recent event on the western and

eastern segments as considerably different.

Suggests that the segments rupture independently.

Dip-slip/normal down to the south.

Other faults that were investigated included the Kouga Fault and the Paul

Sauer fault zone:

Lack of deformation observed on several Tertiary surfaces along the extent of

the Kouga fault.

At site M2.60 the unconformity between the Tg surface and underlying

Paleozoic bedrock was mapped and observed to be unfaulted.

The author concludes that nowhere along the 35 km trace of the Kouga fault

that they traversed was the Tg surface displaced by a fault. Further, high

resolution airphoto reconnaissance was used to investgate surfaces that could

not be reached in the field. This reconnaissance showed no fault scarps at an

approximate resolution of 0.5 m. The scarp detection was limited by the gaps

between the Tg surfaces, suggesting that no post-Miocene ruptures longer

than 6±2 km with displacement of ≥0.5m could have escaped their attention.

The Paul Sauer fault zone offsets the western portion of the Kouga fault zone

in a series of 15-20 km long north-northeast-striking cross faults.The author

investigated a site along the Paul Sauer fault (K2.016) and determined there

was evidence for no displacement since Miocene time with the assumption that

the Tg gravels are Miocene in age.

The author investigated several sites along the Baviaanskloof fault. These sites

showed very convincing evidence for no displacement across the Tertiary


231


Is The Data

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SSC Model?


gravel surface. Site M1.133 contained fractures within the silcrete caprock,

however, the author determined that there was no vertical displacement across

the zone of fracturing. Further, he attributed the observation of southward

thickening in the gravel units to depositional onlap..

Partridge A Review of Existing Data on

Neotectonics and

Palaeoseismicity to Assist in the

Assessment of Seismic Hazard at

Possible Nuclear Power Station

Sites in South Africa

1995 Reviews and summarises neotectonic evidence in southern Africa in relation to

three proposed nuclear power plant sites.

Document summarises previous work conducted in South Africa.

Document cites Hill (1988) for recognizing a 4 m high fault scarp.

Deposition of the offset alluvial fans could be correlative to periods of elevated

precipitation levels during marine oxygen isotope stage (MIS) 3 (60–21 ka) and

the warming that followed the waning of the Last Glacial Maximum (~16–12 ka;

Partridge, 1990). By extension, this document suggests that the offset is post-

60 ka.


probability

KLH

Prasad & Claasen Report on the Baviaanskloof Fault

Segment of the Ceres Kango-

Baviaanskloof-Coega Fault

System: Neotectonic Studies for

Evidence for Possible Post-

Tertiary Grahamstown Formation

(Tg) Reactivation of the Fault

2012 Field reconnaissance showed no evidence of displacement of the Tg surfaces

or Quaternary alluvial gravel terraces along the Baviaanskloof Fault.

Slow uplift rates of 5.4 m/My for drainage basins are indicative of a tectonically

stable landscape and an inactive Baviaanskloof Fault.

MEMA

Rath & Cole Ground Geophysical Survey

Investigating a Feature Identified

During the Airborne Geophysical

Study of the Area Around

Thyspunt

2007 Performed a resistivity study across a fault inferred along a magnetic anomaly

(SV1). The results corroborate the existence of a fault. The age of the fault

cannot be established based on this work.


probability

MEMA

Satriano et al. The 2012 Mw 8.6 Sumatra

Earthquake: Evidence of

Westward Sequential Seismic

Ruptures Associated to the

Reactivation of a N-S Ocean

Fabric

2012 Discusses the tectonic setting of the 2012 M 8.6 Sumatran earthquake. It

concludes that the earthquake occurred in a diffuse zone of deformation.


2012 M 8.6 Sumatran earthquake (not

considered to be good analog)

MEMA/ KLH

Shone et al. Pre-Cape Rocks of the Gamtoos

Area—A Complex

Tectonostratigraphic Package

Preserved as a Horst Block

1990 p. 616—

Preliminary results indicate that the entire pre-Cape succession in the

Gamtoos area has undergone multiple episodes of folding and thrusting.

p. 617—

Two major normal faults, the Gamtoos and Elandsberg, delineate the NE and

Yes Relative ages of faults in the Gamtoos

region (crosscutting relationships)

(8.4.3).

GIS_S0071_F2 MEMA/

KLH


232


Is The Data

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SSC Model?


SW margins of the pre-Cape outcrop. Two southward-dipping thrusts: the

Keurkloof and Saagkuilen.

p. 619—

The Elandsberg Fault is near vertical and becomes a 150 m wide shear zone

at its NW extremity. The Gamtoos Fault dips southwards and does not have a

broad shear zone.

N-S-trending faults (e.g., Boskloof and Otterford) displace the Elandsberg Fault

and therefore are younger than the Elandsberg Fault.

p. 620—

The Elandsberg fault zone has stretched pebbles and could be a reactivated

formerly deep-seated shear zone, possibly of Pan-African age. Other normal

faults (e.g., the Gamtoos) are more typical of shallow brittle-zone deformation.

Shone & Booth The Cape Basin, South Africa:

A Review

2005 Abstract—

Sedimentary rocks of the Palaeozoic Cape Supergroup, Natal Group, and

Msikaba Formation were deposited on a passive continental margin in a variety

of terrestrial and shallow marine-shelf depositional environments, from the

early Ordovician until the mid-Carboniferous. Tectonism, which took place

between 278 Ma and 230 Ma, affected only the Cape Supergroup rocks and

resulted in the Cape Fold Belt. Rocks of the Natal Group and Msikaba

Formation were not tectonised. In the Cape Fold Belt, the presence of thrust-

stacked successions, together with evidence of thrust-eliminated pelitic units,

cast doubt on the reliability of some aspects of the accepted lithostratigraphy.

In spite of deficiencies in the available database, it is possible broadly to

reconstruct the probable basin history; a rifted continental margin seems a

likely setting for the Cape Supergroup, Natal Group, and Msikaba deposits.


MEMA

Umvoto Africa

(PTY) Ltd

Deep Artesian Groundwater for

Oudtshoorn Municipal Supply

Phase D Target Generation &

Borehole/Wellfield Siting Using

Structural Geology and

Geophysical Methods

2005 This report reviews the geological data from a hydrostratigraphic and structural

perspective and develops the basis for a tectonic and hydromechanical

approach to groundwater exploration and development. To define target sites

for deep drilling, the structural geology and geometry of the large-scale

fracturing is analyzed from satellite images and aerial photographs at different

scales so as to determine its dependence on scale of observation and rock

type. Quantitative data was gathered through 2-D GIS-based mapping

augmented by outcrop-based studies of fracture sets.

The Schoemanshoek–De Rust Fault bend, the Stompdrift fold, and other minor

faults exposed at the surface to the SE of De Rust are parts of a complex

“accommodation” or “transfer” zone between two major segments of the Kango

Yes Structural Kango Fault segmentation

(8.4.1) (and Eastern Cape Fold Belt

virtual faults orientation) (8.3.1).

GIS_S0085_F3

.4

KLH


233


Is The Data

Used in the

SSC Model?


Fault. The Stompdrift accommodation zone would have formed at a relatively

late state in the evolution of the Kango fault system, when formerly separate,

en-echelon segments became linked, and their displacement fields began to

interfere via the development of cross-faulted and cross-folded structures,

parts of which may now be buried beneath the Cretaceous strata to the west of

the Toorfonteinkloof Fault bend.

Five systematic fracture sets are identified (in descending order of frequency):

NNW/SSE (N350°E)

NNE/SSW (N005°E)

NW/SE (N325°E)

WNW/ESE (N300°E)

W/E (N240°E and N280°E)

Inversion Structures

Facenna et al. The Influence of Pre-existing

Thrust Faults on Normal Fault

Geometry in Nature and in

Experiments

1995 This report examines the influence of the geometry of reactivated thrusts by

normal faults. The report examines case studies as well as laboratory studies.

The study finds that when the dip of the thrust fault is <32°, an unlinked listric

normal fault occurs, whereas, if the pre-existing dip is >32° but <42°, there is a

linked planar normal fault; and, finally, if the dip of the thrust is >42°, complete

reactivation of the pre-existing thrust plane occurs during normal faulting.

A case study analogue for the <32° reactivation is taken from the Central

Apennines, where the pre-existing shallow-dipping thrust fault has had little

effect on the dip of the normal fault. However, the low strength of the rocks

surrounding the thrust plane influences the general preferred location for the

inversion structure/normal fault (i.e., the diminished strength of the crust from

thrust faulting).

No Provides minimum dip angles for

inversion structures.

RC

Van der Merwe &

Fouché

Inversion Tectonics in the

Bredasdorp Basin, Offshore South

Africa

1992 Abstract—

There were three distinct post-rift inversion events in the Bredasdorp Basin.

p. 50—

The youngest normal faults displace the base Tertiary unconformity (also

Figure 3).

p. 58—

Post-1At1 compression resulted in the folding and tilting of syn-rift sediments.

This deformation is at least Albian age (112–99.6 Ma).

No

Mesozoic Basins and Faults

Bate & Malan Tectonostratigraphic Evolution of

the Algoa, Gamtoos and Pletmos

1992 p. 71—

The kinematic history of the structurally influenced Algoa, Gamtoos, and

Yes Fault structure, Gamtoos Fault (8.4.3)

Seismic data suggest that Gamtoos

GIS_S0014_T1 MEMA/

KLH


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Basins, Offshore South Africa Pletmos Basins can be summarised as follows:

The breakup of East and West Gondwana in the Middle to Late Jurassic

initiated the negative inversion of the Cape Fold Belt thrust faults. This created

localised depressions in the hanging-wall blocks forming the Mesozoic

depocenters.

Tectonics controlled synrift sedimentation.

Seismic data suggest that the Gamtoos Fault is a single discrete fault plane.

However, fieldwork indicates that the Gamtoos Fault may be a segmented fault

zone comprising both the Gamtoos and Elandsberg Faults. A similar situation

may extend offshore below seismic resolution. Segmentation of the St Croix

and Port Elizabeth boundary faults shows fault planes with their long axes

parallel to the dip surfaces of the fault planes.

Syn-extensional rotation of the hanging-wall successions along arcuate faults

resulted in localised uplift and inversion features.

Further active rifting related to the breakup of southern Gondwana terminated

in the late Valanginian (~136 Ma). This was followed by thermal subsidence

and late tilting of the basins.

Fault is a discrete fault, but there is

onshore field evidence for more than

one fault. The onshore and offshore

may be different.

Brown et al. Sequence Stratigraphy in

Offshore South African Divergent

Basins

1995 p. 19—

The Pletmos Basin covers about 10,000 km2 and is filled with post-rift

Cretaceous rocks. It is bounded on the NE by the St Francis Arch and on the

SW by the Infanta Embayment. The basin is made up of five subbasins, which

are grabens. Three main faults (Plettenberg, Superior, and Pletmos) control

the basins. Although the fault systems were initiated during rift onset, they

continued to impose significant structural control on the basin complex during

most of its post-rift Cretaceous history.

Rifting began during the Middle to Late Jurassic. Normal faulting and synrift

deposition continued until the early Valanginian, at ~126 Ma. Widespread uplift

occurred north of the Agulhas-Falkland Fracture Zone. Cycles of subsidence

continued until ~112 Ma with the final movement of the Falkland Plateau

westward past the Agulhas Platform. This event generated massive uplift and

an unconformity. After the Falkland Plateau cleared the African Plate, thermally

driven subsidence began to dominate the Pletmos subbasins in four

supercycles.

Late Cretaceous and Cenozoic extensional stress generated by thermally

driven subsidence initiated many shallow normal faults and locally reactivated

movement along the major rift faults.

Yes Mesozoic reactivation of compressional

structures (8.3.2)

Characterisation of the Plettenberg

Fault (8.4.4)

Mesozoic history of the Pletmos Basin,

many interpreted seismic profiles.

Fig. 17 summarised depositional history

of the basin.

Fig. 13 shows fault locations.

GIS_S0083_F1

3

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KLH


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p. 82—

Each third-order sequence in the Pletmos Basin has been tentatively

correlated with sequences in the Bredasdorp and Orange Basins.

About 55 fourth-order sequences have been mapped between 126 and 77.5

Ma in the Pletmos Basin, many more than are recognised in other South

African basins.

Du Toit Mesozoic Geology of the Agulhas

Bank, South Africa

1976 Abstract—

The Horizon D reflector is the base of the Mesozoic. Horizon C is an

unconformity within the Lower Cretaceous, A is the base of the Upper

Cretaceous, and is within the upper Cretaceous. Mapping is based on 17

boreholes and ~24,000 km of seismic reflection profiles.

Yes Fault geometry of the Gamtoos Fault

(8.4.3), Plettenberg Fault (8.4.4) and

Worcester Fault (8.4.5)

Plate 1, Horizon D is used for offshore

fault locations.

Seismic profiles are used for fault

characteristics.

HorizonD_fault

s

MEMA/

KLH

Fouché et al. Plate Tectonic Setting of the

Mesozoic Basins, Southern

Offshore, South Africa: A Review

1992 Paper is largely a synopsis of the understanding of the tectonic relationship

between the Mesozoic basins of southern offshore, South Africa and

Gondwana tectonics, and the relationship with the underlying Cape Fold Belt.

There is brief discussion of inversions along structures such as the Kango

Fault.

No RC

Johnston The Cape Fold Belt and Syntaxis

and the Rotated Falkland Islands:

Dextral Transpressional Tectonics

Along the Southwest Margin of

Gondwana

2000 Abstract—

The Cape Syntaxis, and the partially obscured Port Elizabeth Antitaxis, are

oroclinal bends of the Cape Fold Belt that developed in response to continued

dextral shear along the Gondwanide belt. Clockwise rotation of the Falkland

Islands occurred in two stages: (1) ~90° during oroclinal bending (the islands

were incorporated in the short east limb of the Port Elizabeth Antitaxis), and (2)

>60° during solid body rotation about the Euler Pole to the Agulhas-Falkland

Fracture Zone (AFFZ), a major dextral transform fault that propagated through

the hinge region of the Port Elizabeth Antitaxis during breakup of Gondwana.

p. 5—

The bend in faults near Port Elizabeth is assumed to be due to a pre-Jurassic

structure that is the same age as, and may have formed in fashion similar to,

the Cape Syntaxis. It is referred to as the Port Elizabeth antitaxis because the

bend is opposite of the syntaxis.

p. 9—

The development of the Cape Syntaxis and the Port Elizabeth Antitaxis, and a

significant proportion of the rotation of the Falkland Islands may be additional

manifestations of the dextral transpressive character of the Gondwanide

Yes Origin of bend in Mesozoic basins.

Potential link between formation of the

syntaxis and the Port Elizabeth antaxis.

MEMA


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orogen. The Cape Syntaxis and Port Elizabeth Antitaxis form NE-trending

hinge zones oriented sub-perpendicular to the NW trend of the South American

and Antarctic portions of the Gondwanide belt. They are, therefore, oriented at

a high angle to the presumed main margin-parallel transport direction of the

crustal block south of the Gondwanide orogen.

p. 10—

Subsequent to orocline development, the hinge region of the Port Elizabeth

Antitaxis may have acted as a zone of weakness along which the AFFZ

propagated during separation of South America from Africa.

Kijko et al. Phase 1: Preliminary Statement of

Seismic Hazard for Port of

Ngqura, Port Elizabeth

2006 Kouga Fault had instrumental seismicity.

Coega Fault is active based on 12 January 1968 M 5.5 earthquake.

Last activity on Gamtoos Fault—Mid-Tertiary (23–5 Ma), Port Elizabeth Fault

(Lower Tertiary), Baviaanskloof, and Paul Sauer (Cretaceous–recent).

No Table 6.1 interprets length and age of

last activity on faults near Port

Elizabeth.

MEMA

McMillan et al. Late Mesozoic Sedimentary

Basins off the South Coast of

South Africa

1997 Abstract—

Late drift sedimentation since the Aptian has led to the steady southwards

development of the continental shelf and the formation of an elongate basin

parallel to the relict shelf break (the Outeniqua Basin). The basin is composed

of essentially mid-Aptian to Maastrichtian deposits and overlies the pre-existing

rift basins with transverse structural grain.

During Portlandian to Berriasian times, the area of sedimentation in the

Gamtoos Basin appears to have enlarged considerably towards both the St

Francis Arch and the Recife Arch.

Profile (Figure 17) shows Gamtoos deforming Tertiary strata.

The Gamtoos anticline is a feature attributed to tectonic strain along the

Agulhas-Falkland Fracture Zone (AFFZ). Reverse and strike-slip faulting are

also known from this time.

There is a thin veneer of Pleistocene and Holocene sedimentation in the

offshore basin.

Onshore, the Gamtoos half graben ceased active subsidence and

sedimentation after unconformity of Hauterivian to earliest Barremian age

(~115 Ma). There was profound erosion offshore during this time. This

unconformity might be related to the proximity to the uplifting marginal fracture

ridge.

p. 359—

Onshore, the Gamtoos Fault throw is 3 km; offshore, the fault is traced to a

depth of 12 km.

Yes Gamtoos Fault (8.4.3), Plettenberg

Fault (8.4.4)

Timing of sedimentation and faulting in

the offshore

Location of major basin-bounding faults

Probability of activity of faults

Sense of slip

Dip of faults

GIS_S0075_F1

and F25

RC/MEMA/

KLH


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SSC Model?


Superior Fault (Figure 14) and Port Elizabeth Fault (Figure 19) are interpreted

to cut into Tertiary strata.

p. 348—

The Superior Fault has strike-slip motion after the 6At1 unconformity.

St Croix Fault is interpreted to not disturb Campanian (83.5 Ma and later)

sediments (Figure 20, profile J-J′).

Cross sections over the southern end of the fault complex, along the hinge of

St Francis Arch, indicate the fault offsets the 1At1 seismic reflector sequence

boundary and overlying sediments up to the 6At1 boundary (~116.5 Ma; see

section GG′, Fig. 1, p. 320; Fig. 3, p. 325, and Fig. 17, p. 361). Overlying latest

Aptian sediments (109.5–108 Ma) are not faulted in this area. Over the arch

itself, sediments were eroded down to and past the 1At1 boundary, due to

proximity to the uplifted fracture ridge passing along the AFFZ. The Falkland

Plateau cleared the tip of South Africa around the late Albian, with elevated

conditions continuing into the Cenomanian. The offshore uplift and erosion

resulted in formation of several canyons within the offshore basins. The

southern NNW-SSE segment of the Cape St Francis Fault was therefore last

active ~116.5 Ma.

Nolte Structure and Tectonostratigraphy

of the Gamtoos Belt Between

Tweewaters and Classen Point,

Eastern Cape Province, R.S.A.

1990 Abstract—

The Gamtoos Belt is preserved as a horst. The reverse Elandsberg Fault and

the normal Gamtoos Fault form the NE and SW boundaries, respectively.

Transfer faults, developed normal to the strike of the boundary faults, cut the

horst into several blocks. Polyphase fold-thrust deformation is evident from the

Gamtoos rocks in each block. Northward-directed compression resulted in

predominantly recumbent, isoclinals folds, often displaced parallel to their axial

planes by thrusts. Four phases of deformation are recognised in the Gamtoos

Belt.

p. 1—

Earliest records of mining are from 1792 (silver and lead) by the Maitland River

mouth. Currently, limestone is quarried in the Gamtoos Valley (locations where

faults are visible).

p. 6—

Kent (1980) proposed “Gamtoos Formation”; Toerien and Hill (1986) proposed

“Gamtoos Group”.

p. 8—

In horst block, detached fold limbs were displaced along bedding-parallel

Yes Map location of Gamtoos Fault (8.4.3)

Probability of activity (Elandsberg Fault

and NE-trending cross faults)

Style of faulting

Sense of slip

GIS_S0078 MEMA/ KLH


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SSC Model?


foliation, which in turn is parallel to the axial planes of the recumbent isoclinal

folds in the study area. Adjacent fault blocks show differential vertical

displacement, resulting in discontinuity between units across transverse faults.

p. 14—

The term “Gamtoos Formation” should be abandoned because the area is too

faulted. Author prefers “Gamtoos fold belt” or “Gamtoos deformation belt”.

p. 20—

Rocks are mostly carbonates and rudites, and lithologies are predominantly

arkosic.

p. 25—

The lateral termination of the Kaan allosynthem occurs via transfer faults

stepped down to the SE and NW at Lime Bank and Tweewaters, respectively.

Gamtoos rocks have been subject to low-grade regional metamorphism

(Tankard et al., 1982).

Common lithologies—Oolitic and crystalline limestone, calcareous to

noncalcareous phyllite, arenites (greywackes, subarkoses, and lithic arenites),

and thick conglomerate and grit horizons.

p. 26—

Martini (1987) correlated the limestone in the Gamtoos Group to those in the

Kango Group.

Kaan allosynthem—all carbonates in study area.

p. 27—

Keurkloof thrust is the series of thrust faults.

p. 28—

Thrust and normal faults are visible in the walls of the Pretoria Portland

Cement quarry on the farm Lime Bank 173.

p. 31—

The coastal outcrops near Maitland are covered by the strata of the Algoa

Group and a thick soil cover.

p. 42—

Unconformable, scattered, high-level terrace deposits may be partly coeval

with the Alexandria Formation. The oldest of these deposits could be outliers or

equivalents of the Early Tertiary Grahamstown or Martindale Formations.

Consist of sandstone and quartzite blocks cemented by siliceous or

ferruginous material. Up to 40 m thick, but generally <6 m thick. Terraces

generally capped with silicrete.


239


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p. 43

The Gamtoos Belt along the coast is often covered by strata of the Algoa

Group. The northern limit of the formation roughly coincides with the 300 m

contour, above which coeval silicrete or high-level fluvial gravels of presumably

Tertiary age occur. The Alexandria Formation (littoral) has an unconformable

lower contact occurring at Claaskraal 26 and Yellowwoods estate 493.

p. 135—

Geomorphic features indicative of pre-Cape structural control are southward-

draining rivers along the coast and minor streams in the Gamtoos Valley. The

former alter course sharply when crossing E-W-striking boundary faults, while

the latter usually drain through synforms.

p. 166—

The Elandsberg Fault appears to predate the other faults in the area.

On aerial photographs, both the Gamtoos and Elandsberg Faults may be

recognised by differences in their vegetation. Dense bush grows on the

Gamtoos Belt, fynbos on the Table Mountain Group, and less dense bush on

the Kirkwood Formation to the south.

p. 167—

Gamtoos Fault—The straight trend of the fault trace probably indicates a

steeply dipping fault plane. No breccias were found along this fault contact. It is

not displaced by any other fault and is considered to be the youngest in the

area. To the south is the Uitenhage Group.

A series of transfer faults, at a high angle to the strike of the Gamtoos Fault are

arranged in an en-echelon pattern between Van Stadens and Maitland Rivers

along the coast.

p. 171—

Three types of thrust faults in the area: (1) foreland-dipping duplex structures,

(2) emergent imbricate fan structures, and (3) back thrusts.

p. 184—

At least four, and possibly five, phases of deformation (D1–D4). D4 structures

are related to extensional tectonics.

p. 185—

The greater spread of bedding poles near the coast (sub-area 3) may possibly

be related to slight (post-D3) clockwise rotation on the fault blocks between the

Elandsberg Fault and the right-lateral Gamtoos shear zone.

p. 210—


240


Is The Data

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SSC Model?


The sediments of the Gamtoos Belt were probably deposited in a graben-

basin, which may have formed as a result of crustal subsidence and orogenic

uplift.

p. 217—

the horst may have acted as a rider on the Elandsberg Fault plane since Cape

deformation about 250 Ma. The final extensional plane produced the Gamtoos

Fault, the related basin margin transfer faults and the right-lateral Gamtoos

shear zone.

Paton Influence of Crustal Heterogeneity

on Normal Fault Dimensions and

Evolution: Southern South Africa

Extensional System

2006 Abstract—

Establishment of a seismic–stratigraphic framework for the Pletmos and

Gamtoos offshore basins reveals that the faults established their long lengths

(160 and 90 km, respectively) within 6 Myr of rift initiation prior to accruing their

substantial displacement (16 km). Furthermore, there is no evidence for the

development of intra-basin faults.

The southern South Africa extensional system presents an end member case

of structural inheritance where extensional structures are parallel to and

reactivate underlying compressional structures. In this study structural

inheritance is considered to have a significant effect on mechanisms of fault

growth. The pre-existing structures not only result in the rapid establishment of

fault lengths of up to 160 km, but, additionally, to strain being localised onto the

pre-existing fabric to such an extent that no intra-basin faults evolve and strain

is accommodated entirely on the bounding faults.

p. 875—

At approximately 30 km from the western tip of the Gamtoos Fault, there is a

SW-NE-trending fault that links the Gamtoos and Elandsberg Faults.

The Gamtoos Fault continues to the SW, where it is not exposed because of

Quaternary deposition, although its trace can be directly linked to that of the

offshore fault. The total length of the onshore Gamtoos Fault is 80 km.

There is no bathymetric expression of either the Plettenberg or Gamtoos fault

planes.

p. 876—

Despite the change in trend of both of the faults from a WNW-ESE to a N-S

orientation, the cross-sectional geometry of the faults remains the same along

the entire length of the faults.

p. 881—

Length of fault array: 170 km (onshore and offshore Gamtoos).

Yes Kango Fault (8.4.1), Gamtoos Fault

(8.4.3), Plettenberg Fault (8.4.4)

Offshore fault geometry.

Mmax (segmentation)

Rupture geometry

Seismogenic probability

Seismogenic thickness

GIS_S0079_F4

b and 5b

MEMA/ KLH


241


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SSC Model?


Gamtoos, Kango, and Baviaanskloof can be considered part of the same 480

km long fault system.

p. 884—

The pre-existing Cape Fold Belt fabric has exerted a significant influence on

the development of the Mesozoic South African extensional system, as

evidenced by the following:

The fault arrays are composed of a number of coalesced segments that have a

linear, rather than en-echelon, trend.

The underlying reactivated compressional fault system, probably in

combination with lithospheric constrains such as elastic thickness and

rheology, has resulted in very long fault arrays (>160 km) with high-angle fault

planes (45–60 degrees) and large displacements (16 km).

Near-vertical D–L growth profiles are observed.

Strain is rapidly localised onto the bounding faults, resulting in an absence of

intrabasin faults even during the earliest resolvable syn-rift episode.

Paton & Underhill Role of Crustal Anisotropy in

Modifying the Structural and

Sedimentological Evolution of

Extensional Basins: The Gamtoos

Basin, South Africa

2004 Abstract—

There is no evidence at the resolution of the data of fault segmentation,

isolated depocentres, or intrabasin faults progressively coalescing during the

syn-rift interval.

The evolution of the (Gamtoos) Basin does not conform to current fault growth

models, and it is proposed that its unusual and complex development can be

attributed to the underlying crustal-scale anisotropy.

Yes Gamtoos Fault (8.4.3) segmentation MEMA/ KLH

Paton et al. Applicability of Thin or Thick

Skinned Structural Models in a

Region of Multiple Inversion

Episodes; Southern South Africa

2006 Abstract—

Regional-scale cross sections through the Permian-Triassic Cape Fold Belt

reveal that it comprises two main structural domains: a northern domain

dominated by northward-verging and asymmetric folds; and a southern domain

comprising a series of approximately 8 km wavelength box folds. The genesis

of these box folds is attributed to motion on underlying high-angle (>45)

reverse faults. This variation between north and south in the fold belt is

reflected by a similar variation in extensional geometry of the Mesozoic normal

faults, as revealed by subsurface data.

The normal faults demonstrate a progressive increase in dip from 24 degrees

in the north to 60 degrees in the south.

p. 1940—

The Gamtoos Fault has a very similar geometry to that of the Plettenberg

Fault, and although it also has an E-W trend, the N-S trend is more dominant

Yes Plettenberg Fault (8.4.4.)


GIS_S0073_F8

_ division

between thick

and thin

skinned.

MEMA/ KLH


242


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SSC Model?


at the eastern margin of the basin. In cross section, the fault plane has a planar

geometry to at least 5,000 ms, equivalent to 11,000 m, a depth-converted dip

of 42.5, and a displacement of 16,500 m (Fig. 6B). The offshore fault is a direct

continuation of the Gamtoos Fault, which dissects Section B.

Cape Fold Belt—Given the geometries of the folding—in particular, features

like the syncline to the south of fold A4—it is likely that the principal

décollement is below the Cape Supergroup and within the Pre-Cape Group.

p. 1944—

Observed Mesozoic syn-rift fault throws that increase towards the south (Port

Elizabeth, Gamtoos, and Plettenberg Faults, respectively) may be a

consequence of the south-dipping nature of a mega-detachment.

p. 1945—

The Cape Fold Belt cannot be classified as either a thin-skinned or thick-

skinned tectonic end member as these characterisations do not adequately

describe the features that have been observed. Instead, it is more useful to

describe the deformation as being controlled by a south-dipping mega-

décollement that exhibits aspects of both end members.

Stankiewcz et al. Initial Results from Wide-Angle

Seismic Refraction Lines in the

Southern Cape

2007 Abstract—

The listric geometry of the Kango and Gamtoos Faults can be seen in seismic

refraction to a minimum depth of 15 km (illustrated on Figs. 4 and 6).

Yes Subsurface geometry and seismogenic

thickness of Gamtoos (8.4.3) and

Kango Faults (8.4.1)

MEMA/ KLH

Stankiewicz et al. Crustal Structure of the Southern

Margin of the African Continent:

Results from Geophysical

Experiments

2008 Performed several geophysical studies along a transect in southern Africa

including seismic refraction.

Kango Fault—Low dip, listric at 10–12 km (Figs. 5 and 12).


Geometry

KLH

Thomson Role of Continental Break-up,

Mantle Plume Development and

Fault Reactivation in the Evolution

of the Gamtoos Basin, South

Africa

1999 p. 410

Documents the evolution of rifting within the Gamtoos Basin, assessing the

relative roles of Cape Fold Belt and Agulhas-Falkland Fracture Zone (AFFZ)

influence on the style of rifting and establishing the deformation framework in

which they operated. It also addresses the potential influence of mantle plumes

during both the syn and post-rift evolution of the basin.

The Gamtoos Basin is bounded by St Francis Arch to the west and Recife Arch

to the east.

The geometry of the Cape Fold Belt thrusts can readily explain the geometry of

many of the features seen in the Gamtoos Basin half graben.

Fig. 6—Listric geometry of the offshore Gamtoos Fault.

Fig. 7—Listric geometry not apparent.

Yes Offshore, listric geometry, and

seismogenic probability of the Gamtoos

Fault (8.4.3)

GIS_S0070_F1 MEMA/ KLH


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p. 420—

~N-S extension during Valanginian times resulted in the roll-over of syn-rift

sediments in response to extension on the listric Gamtoos Fault as well as

syn/antithetic normal faulting to accommodate hanging-wall deformation.

The basic geometry of the Cape Fold Belt thrusts controlling listric geometry is

also consistent with the inversion seen along the N-S-trending Gamtoos Fault.

p. 421—

The entire length of the Gamtoos Fault appears to have a listric geometry.

Based on the lack of evidence for shortening, the bend in the Gamtoos Fault is

more likely due to pre-existing changes in the Cape Fold Belt strike than to

rotation in association with the formation of the AFFZ.

p. 423—

Mentions strike-slip motion in the Gamtoos Basin during extension.

pp. 423-425—

Mantle plumes may be responsible for initiation of rifting (Karoo plume) and

uplift and erosion from 65 to 35 Ma (Discovery and Velma plumes).

Viola et al. Brittle Tectonic Evolution Along

the Western Margin of South

Africa: More than 500 Myr of

Continued Reactivation

2011 Abstract—

Western South Africa—The oldest features recognised formed during four

compressional episodes assigned to the Neoproterozoic Pan-African evolution.

This history is expressed by subvertical conjugate fracture sets and fits well the

inferences derived from remote sensing. The greatest compressive direction

rotated from NW-SE to NNE-SSW and finally to almost E-W. A subsequent

ENE-WSW-oriented extensional episode is associated with the local effects of

the opening of the Atlantic Ocean and was followed by a second, ca. E-W

extensional episode, linked to the well-acknowledged Mid-Cretaceous (115–90

Ma) event of margin uplift. A Late Santonian (85–83 Ma) NW-SE compressive

palaeostress deformed the Late Cretaceous sequences and was in turn

followed first by a renewed episode of NE-SW extension, and later by ca. NNE-

SSW Late Maastrichtian (69–65 Ma) shortening.

In situ stress measurements were used to perform slip tendency analysis,

which indicates that, under the currently existing stress conditions, WNW-ESE-

and NNW-SSE-striking faults are critically stressed and are the most likely

reactivated, in agreement with the present seismicity.

Yes Reactivation of faults in western South

Africa.

MEMA

Offshore Structures

Adams & Simmons Relocation of Earthquakes in the

Labrador Sea and Southern

1991 The study relocated 98 earthquakes on an extinct transform margin in the

Labrador Sea. The ridge was active between 85 and 45 Ma.

No Possible analogue for AFZ. KLH


244


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Labrador p. 17—

Listric faults formed during continental breakup at the continent-ocean

transition are being reactivated in the current stress regime.

The magnitudes of earthquakes range from 2.7 to 5.6.

The SE Baffin margin was a transform margin. Eighteen earthquake

magnitudes from 1966 to 1987 range from 4.8 to 2.7.

Ben-Avraham Neotectonic Activity Offshore

Southeast Africa and Its

Implications

1995 Abstract—

Possibly Quaternary basaltic intrusives in the northern, oceanic parts of the

Agulhas Plateau and Mozambique Ridge. Fresh, quenched basaltic glasses

lack any significant alteration, suggesting that their eruption took place in the

last few tens of thousands of years. Renewal of tectonic activity probably took

place along several segments of the Agulhas Fracture Zone. A seismic

reflection profile shows that the fracture zone disturbs the seafloor.

Yes Seismogenic probability and location of

Agulhas Fracture Zone (8.4.2)

GIS_S0086 F1 MEMA/

KLH

Ben-Avraham et al. Neotectonic Activity on

Continental Fragments in the

Southwest Indian Ocean: Agulhas

Plateau and Mozambique Ridge

1995 Abstract—

Discusses evidence for young volcanism on the Agulhas Plateau and

Mozambique Ridge.

The active crustal stretching and tensional stresses implied by this relatively

recent tectonism probably cannot be generated by distantly applied plate-

driving torques, such as ridge push, but appear to require buoyancy-related

forces originating in the underlying upper mantle.

Yes Geometry of the Agulhas Fracture Zone

(8.4.2)

GIS_S0088 F9 MEMA/

KLH

Ben-Avraham et al. Structure and Tectonics of the

Agulhas-Falkland Fracture Zone

1997 In submarine physiography, upper-crustal structure as traced from seismic

reflection profiles, and gravity signature, the Early Cretaceous Agulhas

Fracture Zone possess a distinct fourfold segmentation (Figure 1) that appears

largely inherited from a pattern of Middle to Late Jurassic rifts and partly

oceanic embayments.

Yes Geometry of the Agulhas Fracture Zone

(8.4.2)

GIS_S00080

F1b, F9

MEMA/

KLH

Broad et al. Offshore Mesozoic Basins 2006 p. 553—

The Agulhas-Falkland Fracture Zone (AFFZ) began strike-slip movement in the

Early Cretaceous at the onset of drifting and truncated pre-existing structural

trends such as the Permo-Triassic Cape Fold Belt and the Jurassic to Early

Cretaceous graben and half-graben rift complexes of the Outeniqua Basin. The

latter are regarded as failed rifts, any one of which could have opened up and

become mid-oceanic spreading centers.

The synrift and drift phases are not distinct in the Outeniqua Basin as a result

of transform movement along the AFFZ and associated regional structural

effects.



Fault geometry

MEMA/

KLH

Broad et al. South Africa’s Offshore Mesozoic 2012 Summarises the origin and tectonic history of South Africa’s continental No Seismotectonic Setting (Chap. 4) MEMA


245


Is The Data

Used in the

SSC Model?


Basins margins with particular attention paid to the formation of offshore Mesozoic

basins.

Parsiegla et al. Deep Crustal Structure of the

Sheared South African

Continental Margin: First Results

of the Agulhas-Karoo Geoscience

Transect

2007 p. 404—

A depth-migrated section of the seismic reflection line (AWI-20050100)

illustrates the presence of several faults at the position of the Agulhas-Falkland

Fracture Zone (AFFZ) that can be followed from the basement into the

overlying sedimentary wedge, suggesting reactivation of parts of the AFFZ

postdeposition of the sediments.



Fault geometry

Style of faulting


MEMA/

KLH

Parsiegla et al. The Agulhas Plateau: Structure

and Evolution of a Large Igneous

Province

2008 Abstract—

The Agulhas Plateau is made up of overthickened oceanic crust (mean

thickness 20 km) that formed as part of a larger large igneous province (LIP)

between 100 and 94 ± 5 Ma.

p. 348—

Graben-like structures on the northern Agulhas Plateau were interpreted as

remnant structures caused by extensional forces that acted during the

fragmentation of the AP-NEGR-MR LIP.

p. 349—

Thermal subsidence calculations suggest that major parts of the Agulhas

Plateau have probably formed subaerially.


Fault geometry

Northeastern limit of the AFFZ.

GIS_S0090_F2

_Parsiegla_etal

_2008

MEMA/

KLH

Parsiegla et al. Southern African Continental

Margin: Dynamic Processes of a

Transform Margin

2009 Considers southern Mesozoic basins (e.g., the Pletmos and Gamtoos) as part

of the Outeniqua Basin. The Southern Outeniqua Basin is the E-W elongated

basin along the Agulhas-Falkland Fracture Zone (AFFZ).

Abstract—

Two episodes of crustal extension in the Outeniqua Basin: the breakup of

Africa and Antarctica (~165–155 Ma) and an episode associated with a

transtensional component of the shear motion along the Agulhas-Falkland

Transform (~136 Ma). The second phase affected only the southern portion of

the basin.

Cape Supergroup rocks underlie the basin.

The Diaz Marginal Ridge is attributed to either a transpressional episode along

the Agulhas-Falkland Transform or (more likely) to thermal uplift accompanying

the passage of a spreading ridge to the south.

p. 2—

The Outeniqua Basin (Fig. 3) consists of a set of small fault-bounded sub-

basins in the north and a distinctively deeper sub-basin (the Southern

Outeniqua Basin) in the vicinity of the AFFZ. The cause of this variability, the


Age and activity of offshore faults and

basins—specifically, the Outeniqua

Basin.

MEMA/

KLH


246


Is The Data

Used in the

SSC Model?


amount of stretching, and the structure of the crust underlying the basins and

the AFFZ are not understood.

Ben-Avraham et al. (1993) and Thomson (1999) show how shearing on the

fracture zone caused local deformation in neighboring parts of the Outeniqua

Basin.

p. 12—

McMillan et al. [1997] report evidence for strike-slip faulting in the Southern

Outeniqua Basin.

150–200 m of Cretaceous sediments on top of the Diaz Marginal Ridge

indicate the ridge formed after initial movement on the AFFZ. The ridge likely

formed between 130 and 90 Ma. Preferred cause of uplift is thermal due to the

temperature contrast between the hot oceanic and cold continental crust.

Crustal thickness in the Southern Outeniqua Basin is ~21 km.

Neotectonic activity at the AFFZ was identified [Ben-Avraham, 1995; Parsiegla

et al., 2007] and may be an expression of lithospheric weakness along the

AFFZ to accommodate uplift in Southern Africa.

Quaternary Faulting

Butzer & Helgren Late Cenozoic Evolution of the

Cape Coast Between Knysna and

Cape St. Francis, South Africa

1972 p. 120—

Although documentation for the 60 m shoreline is rudimentary, the authors

found absolutely no evidence for either the local faulting or large-scale

upwarping in the Tsitsikamma Forest suggested by Davies (1971) for most

apparent complications to a universal sequence of shorelines at identical

levels. Above all, the Coastal Platform maintains an almost uniform elevation

from west of George to east of Port Elizabeth through the Tsitsikamma Forest,

and any deformations have been limited to minor warping of restricted extent.

No MEMA

Davidson & Smith Geophysical Survey Report for

Thyspunt Eskom Site Surveys

South Africa

2007 This report summarises a marine geophysical survey conducted by Fugro off

the Thyspunt site in 2006.

Most of the rocky outcrop areas slope to the SE at angles of less than 0.5°.

The sediments in the basins slope at slightly steeper angles between 0.85° to

1.1°. Some areas in the central and southern areas of the central basin have

variable slopes to the SE from 0.32° to 0.92°

Faults and slump features do exist in the survey area but no information as to

when they were last active was obtained.

No Considered in the evaluation of the

seismogenic probability of the Cape St

Francis Fault (8.5).

MEMA


Southern and South-Eastern

Cape Province (Part 1)

1971 pp. 211-212—

Pebbles against a cliff at Plettenberg Bay suggest faulting and not marine

deposits. (Site 340)

No Possible fault scarp near Plettenberg

Bay.

MEMA


247


Is The Data

Used in the

SSC Model?


De Beer Investigation into Evidence for

Neotectonic Deformation Within

Onland Neogene to Quaternary

Deposits Between Alexander Bay

and Port Elizabeth—Desk Study

Report

2004 Notes that reactivation of the Kango Fault occurs along a pre-existing structure

that is the boundary between less competent and more competent crust.

The lineament pattern in the Kango fault includes relict features of the Cape

Orogeny.

Yes Rupture geometry


MEMA/

KLH

De Beer Investigation into Evidence for

Neotectonic Deformation Within

Onland Neogene to Quaternary

Deposits Between Alexander Bay

and Port Elizabeth—South Coast

Report

2005 p. 37—

Evidence of neotectonic reactivation—Two small faults with down-to-the-south

displacement of 0.5 m reported by J. Viljoen in a roadcut east of Swellendam

(Fig. 41). Faults end at an unconformity between unit A (channel deposits cut

in Kirkwood Fm, Middle Cretaceous, pre-drift onset, 126 Ma) and unit B

(terrace gravels cut into unit A). Age of unit A is related to post-African surface

sedimentation; 20 m of incision into Bokkeveld Group rocks has occurred since

deposition of unit A, assuming one quarter of the 80 m incised into the Miocene

planation surface since the end of the Miocene at 5.3 Ma, and thus an

estimated age of ~1.3 Ma. (Note: a 4–5 m/Myr uplift rate, based on CN

analyses, would suggest that terrace could be older.)

Worcester Fault is a reactivated Cape Fold Belt thrust; Mesozoic normal fault

(down to the south); steep normal fault with down to the south throw, likely

most active during Middle Jurassic to Middle Cretaceous; maximum

downthrown of 6 km was reached in syntaxis Cape Fold Belt near Worcester.

Yes Worcester Fault (8.4.5)

Probability of activity

Reccurence

Style of faulting

Future earthquake characteristics

Major structures within the Syntaxis

(8.3.2)

RC/KLH

Goedhart Project 1—Desk Study Report: A

Geological Investigation of

Neotectonic Reactivation along

the Ceres-Kango-Baviaanskloof-

Coega Fault System in the

Southern and Eastern Cape,

South Africa

2004 Notes that the Kango-Baviaanskloof section has the greatest potential for

neotectonic reactivation. Described as 118 km of discontinuous scarp 2–4 m

high. Although dominantly normal, there is the possibility of sinistral and dextral

isolated faults in local step-overs.

Source of driving force is not well constrained; proposed models as follows:

– Isostatic rebound resulting from rapid retreat of the Great Escarpment during

the Cretaceous (and Miocene?).

– Uplift of the Eastern Cape coastal region, in relation to the southward

upwarping associated with the African Superswell and extension of the East

African Rift system.

– Possible rotational extension of the easternmost fault strands resulting from

reactivation of the Agulhas fracture zone. Author favors the isostatic rebound

on the margin of the Willowmore gravity low to explain the faulting along the

Kango.

Notes that the Ceres-Kango-Baviaanskloof-Coega (CKBC) fault was initially


Gamtoos Fault (8.4.3)


Geometry

KLH


248


Is The Data

Used in the

SSC Model?


activated in the Palaeozoic to Cretaceous. Author infers that this zone of

weakness is more likely to be reactivated.

Stratigraphy (evidence of early [Mesozoic] faulting): Enon Formation (fluvial

deposit with TMG quartzite and sand stones) lies on the Jurassic igneous

deposits of the Zuurberg Group. The early Enon Formation rudite beds are

coarse-grained and lie generally to the south of the large boundary faults;

bedding generally dips towards the faults, indicating active growth faults at time

of deposition.

Notes that there is an isostatic gravity anomaly coincident with the entire CKBC

fault system. The anomaly appears to behave irrespective of lithologic

contacts. See Smit (1962).

Aerial photo interpretations indicate “four base-level lowering events.” Based

on topographic position of fluvial terraces (p. 86).

Total length (Kango-Baviaanskloof): 118 km.

Dip: 45° (measured from calcretised fault plane exposed at Buffelsvalley

Farm).

Goedhart Project 1: A Geological

Investigation of Neotectonic

Reactivation along the Ceres-

Kango-Baviaanskloof-Coega Fault

System in the Southern and

Eastern Cape, South Africa

2005 This study is a field report of a neotectonic investigation of the Kango Fault.

Recognises the Kango Fault as the only Quaternary fault in South Africa.

Dip-slip/normal down to the south.

This is the follow-up study to the 2004 desk study of De Beer. The field findings

shortened the total length of the fault to approximately 84 km.

Dip: 45° in bank exposure (site M1.26 river site).

The active Kango Fault is split into two sections: the 45 km long western arm

(10 km east of De Rust at site M1.19 to Toorwaterpoort (hot spring activity at

Toorwaterpoort, site 1.91) and the 41 km long eastern arm (site 1.91 to site

1.133). Acknowledges these as provisional subdivisions.

Scarp heights (not corrected to represent net vertical tectonic slip) range from

1 m to 8.5 m. Scarps are higher on the interfluves surfaces (5–8.5 m) and

lower scarp heights in the lower-lying alluvial valleys (1–4.5 m, but typically 3–

4.5 m). Cumulative events are inferred by the differing scarp heights.

Provisional subdivisions considered as possible rupture segments.

“Palaeosol” (dated to 4,660 ± 40 yr BP. The palaeosol is used as a “maximum

age for reactivation”. The sample was taken from a zone in the outcrop 0.6 x 2

m, not from a single discrete sample. Holocene event ≤4336 BC. (Note:

palaeoseismic trenching shows that this dated unit post-dates the most recent

event [Hanson et al., 2012b]).



Fault geometry

Recurrence/Recency

Mmax

KLH


249


Is The Data

Used in the

SSC Model?


P. 21 discusses a possible “actual age of 5,316 years”. It is unclear whether

this is a calibrated date; nonetheless, this is the date used to determine the slip

rate of 0.66 mm/year.

Site M1.57 is a pre-existing bulldozed trench, <2 m deep roughly parallel to the

Kango Fault trace. The trench exposes liquefaction features dated to 5,530 ±

45 yr BP. A spring is located at this site along the scarp.

Site 1.91 (Toorwaterport): natural exposure showing unfaulted deposits dated

to 13,210 ± 60 yr BP. Acknowledged uncertainty that the deposits could be re-

precipitated after fracturing in a faulting event and thence “healing” the

fractures.

Kango Fault west of De Rust: Six sites were visited between the Touws River

and De Rust. Generally, the findings were that there were no disturbances to

the Quaternary deposits in the vicinity of the fault trace. No age dating or

relative age estimates for the undisturbed Quaternary deposits were provided

by the author. At one site near the Prinsrivier Dam, the author suggests that

recent rock fall could have been triggered by a seismic event.

Goedhart Project 1: A Geological

Investigation of Neotectonic

Reactivation along the Ceres-

Kango-Baviaanskloof-Coega Fault

System in the Southern and

Eastern Cape, South Africa:

Trench Report

2006 Palaeoseismic trench report. Trench was 80 m long x 6 m wide x 2.5 m deep.

All surface deformation occurred within a 32 m wide graben.

Single event—Deformation is well bracketed to have occurred between 12,206

and 8,878 yr BP.

Total length: 85 km.

Dip: 67° (trench exposure).

Report expresses uncertainty that the eastern and western traces of the Kango

Fault could rupture independently. Rupture length: either 85 km or 45 km.

Maximum offset measured was 2 m by projecting the fan slope surface across

the main trace of the fault and the south-bounding graben.

Author notes some large scarps on the eastern segment, which could suggest

segmentation.

Author reports that all the units in the trench below the most recent event

(MRE) horizon are offset by the same amount, thus suggesting only one event

is exposed in the trench. (See Hanson et al., 2012b, for reinterpretation.)

Report estimates a Mmax from M 7.18 to M 7.43. References Partridge (1995),

who estimated a M 8.7.

The oldest dated unit near the floor of the trench is 108 ka, suggesting a

recurrence interval of at least this long. The author goes on to conclude that

the basal units appear to be flat-lying deposits; therefore, there was no PE

YES Kango Fault (8.4.1)


Fault geometry

Recurrence/Recency

Mmax

KLH


250


Is The Data

Used in the

SSC Model?


scarp at the time of the deposition of the 108 ka unit. The author cites the

“Machette Criterion” for scarp erosion rate in the semiarid region of the SW,

which estimates 100 ka to erode a scarp completely. Therefore, the author

concludes that the PE could be as old as 100 ka + 108 ka = 208 ka.

A maximum slip rate of 0.0187 mm/year is estimated.

Using an assumed age of 2 Ma (not well constrained) for the oldest offset

straths across the eastern part of the fault zone, the long-term slip rate is

0.00375 (7.5 m scarp/~2 Ma).

The author notes the thickening of unit 2a in the southern margin of the

graben. This observation infers that there is an antithetic fault not observable in

the trench. This could be interpreted as a penultimate fault (p. 52).

Timing of the MRE is constrained between 8,878 ± 452 ky BP) (E26-S1A) and

12,206 ± 723 kyr BP (B17-S1A). This conclusion may stem from the author’s

unintentional interchanging of sample numbers, referring to sample B17-S1A

also as B7-S1A for many pages. Sample B17-S1A is problematic because it is

stratigraphically higher yet older than underlying units. The author states that

the large scatter in sample B17-S1A suggests the date is not precise, but

should be considered a maximum age of the MRE nonetheless. The author

prefers a MRE bracketed between 10,167 ± 507 kyr BP (F15-S1A) and 10,327

± 755 kyr BP (F27-S1A). There are other ages suggested by doing different

age analysis approaches, such as taking the mean of three similar ages, etc.

The general conclusion is that the MRE occurred ~10 ka and not before ~12

ka.

Author suggests that the basal trench units could correlate to marine oxygen

isotope stage (MIS) 5e.

Report concludes that “since the beds above and below the disconformity are

equally offset by the MRE, there was no other faulting during the 105 ka

erosion period”.

Goedhart Onshore and Offshore

Geohazards for the Thyspunt

Nuclear Power Plant: A Summary

of New Airborne and Marine

Geophysical Data, and Existing

Offshore Seismic Reflection Data

2007 Summarises the geological hazards that could threaten the Thyspunt site

including those identified in geophysical surveys. The results indicate that the

Thyspunt site does is not threatened by a serious or “fatal-flaw” type hazard.


Goedhart et al. Surface Geology and Update of

Onland Geological Hazards for

2008 Summarises the surface geology of the site vicinity (40 km) of the Thyspunt

site. Results to date show that the proposed Thyspunt site is not under threat

No Considered in the evaluation of the

seismogenic probability of the Cape St


251


Is The Data

Used in the

SSC Model?


the 40km Site Vicinity and 8km

Site Area Around the Proposed

Thyspunt Nuclear Power Plant,


from any serious potential geo-hazards. Francis Fault (8.5)

Goedhart Late Quaternary Neotectonic

Reactivation of the Kango Fault,

South Africa: Field Estimate of

Extent and Magnitude of Surface

Rupture

2012 PowerPoint presented at TNP SSHAC 3 Workshop 2.

Summary of previous reports and publications.

References earlier studies indicating evidence for Holocene activity.

Presentation has a focus on rupture length for the Kango Fault.

Discussion of uncertainties in endpoints for reactivated fault.

Eastern boundary of the Kango Fault is suggested to be at the Baviaanskloof

thrust (also the Kilpadbeen boundary) or slightly farther west of the thrust.

Notes possible step-over splays at Skilpadbeen boundary.

Dip: Fault dip at site M1.42 is 65°–75° to the south.

Preferred MRE between 10.6 ka and 10.3 ka.

In all scenarios of rupture segments, sites M1.26 and M1.42 are in the same

segment.

Segmentation model notes unfaulted 13 ka deposits at site M1.91; however,

there is uncertainty as to whether the bedrock fault is under the unfaulted

package of alluvium.

Total length of combined western and eastern arm is ~84 km ± 10 long.

Notes fault dip at site M1.42 was 65°–75° to the south.

Estimates vertical surface offset at M1.42 to be 2.0 m (single event).



Fault geometry

Recurrence

Mmax

KLH

Goedhart & Booth Early Holocene Extensional

Tectonics in the South-Eastern

Cape Fold Belt, South Africa

2009 Examines the Kango Fault in addition to the Baviaanskloof and Coega Faults.

84 km long extensional surface rupture; 10,620 ± 509 years ago, based on

OSL ages.

Total length is 320 km.



Fault geometry

MEMA/

KLH

Goedhart & Cole Nuclear Siting Investigation

Program: Remote Sensing

Assessment of the Length of

Aeromagnetic Lineament SV1,

Thyspunt

2007 The aeromagnetic lineament SV1 is estimated to be 15.4 km long. The

certainty of the presence of the lineament varies along length. There is no

geomorphic evidence of the lineament. The results of the study indicate that

SV1 does not pose a threat to the Thyspunt site.


Goedhart & De

Klerk

A High-Resolution Multi-Electrode

Resistivity Survey to Investigate a

Neotectonic Rupture Along the

Kango Fault, near Oudtshoorn,

Southern Cape Fold Belt, South

2011 Conducted a high-resolution resistivity study over a palaeoseismic trench

across the Kango Fault.

Provides constraints on the geometry of the Kango Fault in the upper 70 m.


Fault geometry

MEMA/

KLH


252


Is The Data

Used in the

SSC Model?


Africa

Green & Bloch The Ceres, South Africa,

Earthquake of September 29,

1969: I. Report on Some

Aftershocks

1971 Possible association of Worcester Fault with Ceres area seismicity and

Groenhof Fault (structural step-over from Worcester Fault to De Hoek Fault)

(Fig. 2).

Yes Worcester Fault Zone (8.4.5)


Association of seismicity with specific

structure.

RC/KLH

Hagedorn Silcretes in the Western Little

Karoo and Their Relation to

Geomorphology and

Palaeoecology

1988 Reports preliminary electric spin resonance (ESR) ages of 7.3 and 9.4 Ma for

silcrete caps on pediment remnants in the eastern Little Karoo.

Yes Worcester Fault (8.4.5)

Age of silcrete to determine recency of

movement on regional normal faults.

RC/KLH


Investigations—Marine Terrace

Studies

2012a Coega Fault—Unfaulted Tg surfaces appear to have been relatively stable for

~2 Myr, based on cosmogenic geochronologic results (Bierman, 2012b).

Marine terrace sequences show no evidence for differential uplift across the

projected trends of Cape St Francis Fault Oyster Bay to St Francis shore-

parallel profiles A-A′ and B-B′.

Yes Timing and recency of regional fault

movement.

Seismogenic probability assessment of

Coega Fault (8.5)

RC/KLH

Hattingh &

Goedhart

Neotectonic Control on Drainage

Evolution in the Algoa Basin,

Southeastern Cape Province

1997 Abstract—

Tectonic tilt in the in the Algoa Basin not only resulted in a unidirectional shift of

approximately 15 km of the Sundays River course since the Late Miocene, but

also accelerated the sediment supply rate to the alluvial basin and increased

the ratio of gravel to fine-grained sediment in the basin of the Bushman’s River.

The drainage pattern and recent incision suggest that some underlying faults

and joints have been reactivated. Ruptured Neogene marine and aeolian

deposits displaying vertical throws of up to 11 m indicate extensional rifting.

This may be related to the Agulhas Fracture Zone.

p. 44—

The reactivation of major Permo-Triassic joints as normal faults in Palaeozoic

strata along the Gamtoos Basin western margin suggests stress release in an

extensional environment rather than the recurrence of compression (Hill,

1988).

p. 46—

the Bushman’s River in the Algoa Basin has a number of entrenched

rectangular “meander bends”. The river pattern mimics the rectangular jointing.

Terraces range from 220 m to 40 m above the present river bed.

p. 50—

Neotectonic faults on the Algoa Basin margin are likely to have occurred where

basin margin Permo-Triassic joint sets have been reactivated.

The combination of fault orientation and distribution, episodic eastward

No Considered evidence for recent fault

reactivation in the Algoa Basin, but did

not use directly in specific fault

characterisations.

MEMA/

KLH


253


Is The Data

Used in the

SSC Model?


migration of the Sundays River, late Pliocene warping of the coastal region,

reactivation of Permo-Triassic joint sets, and the presence of Quaternary

faulting in Palaeozoic rocks surrounding the adjacent Gamtoos Basin (may be

referring to Paul Sauer Fault [Hill, (1988], which is questionably active) strongly

suggests episodic rejuvenation of the Zuurberg fault complex along the NE

boundary of the Algoa Basin. Since strain must pass along existing faults,

neotectonic reactivation of other faults in the Algoa basin is also a probability.

The presence of small reverse faults at the Coega Fault NE of Port Elizabeth

supports the proposal.

p. 51—

The Neogene to Quaternary tectonic activity suggests that the southern part of

the Eastern Cape is experiencing tectonism that has influenced river deposition

as recently as the Holocene. This is related to recent tectonic activity along the

Agulhas Fracture Zone.

Hecker et al. Normal-Faulting Slip Maxima and

Stress-Drop Variability: A

Geological Perspective

2010 The authors present an empirical estimate of maximum slip in continental

normal-faulting earthquakes and present evidence that stress drop in intraplate

extensional environments is dependent on fault maturity. A survey of reported

slip in historical earthquakes globally and in latest Quaternary

palaeoearthquakes in the Western Cordillera of the United States indicates

maximum vertical displacements as large as 6–6.5 m. A difference in the ratio

of maximum-to-mean displacements between data sets of prehistoric and

historical earthquakes, together with constraints on bias in estimates of mean

palaeodisplacement, suggests that applying a correction factor of 1.4 ± 0.3 to

the largest observed displacement along a palaeorupture may provide a

reasonable estimate of the maximum displacement. Adjusting the largest

palaeodisplacements in the authors’ regional data set (∼6 m) by a factor of 1.4

yields a possible upper-bound vertical displacement for the Western Cordillera

of about 8.4 m, although a smaller correction factor may be more appropriate

for the longest ruptures. Because maximum slip is highly localised along strike,

if such large displacements occur, they are extremely rare.

Static stress drop in surface-rupturing earthquakes in the Western Cordillera,

as represented by maximum reported displacement as a fraction of modeled

rupture length, appears to be larger on normal faults with low cumulative

geologic displacement (<2 km) and larger in regions such as the Rocky

Mountains, where immature, low-throw faults are concentrated. This

conclusion is consistent with a growing recognition that structural development

No RC/ KLH


254


Is The Data

Used in the

SSC Model?


influences stress drop and indicates that this influence is significant enough to

be evident among faults within a single intraplate environment.

Mitha Subsurface Neotectonic

Investigation of the Eastern Part

of the Coega Fault Corridor,


2013 Eastern Coega Fault—No apparent step in wave-cut platform. Yes Assessment of seismogenic probability

of the Eastern Coega Fault (8.5).

RC

Muller et al. The Detection of the Klippepunt

Low Angle Strike Fault by a

Medium Sensitivity Aeromagnetic

Survey

1986 Interprets an aeromagnetic survey flown over the Thyspunt site and identifies

steeply south-dipping contacts. One contact is interpreted to be W-NW-

trending strike fault south of Thysbaai.


Norman et al. A Preliminary Assessment of

Regional and Coastal Geology

from Cape St Francis to the

Tsitsikamma River with the View

to the Selection of Candidate

Sites for a Nuclear Power Station

1986 Identifies five sites along the southern African coastline as potential sites for

siting a nuclear power plant and maps the geology.


Norman et al. Final Report on the Geology of

the Area Between Cape St

Francis and the Tsitsikamma

River Mouth, Eskom Eastern

Cape Project—Vol. 1: Geological

Description of the Project Area

1987a Summarises the results of the geological mapping, geophysical surveys and

drilling that were conducted in the area between Cape St. Francis and the

Tsitsikamma River mouth.


Raubenheimer et

al.

Detailed Geology of De Hoek,

Thyspunt and Tony’s Bay. Volume

1: Geological Description

1988 Examines potential sites for nuclear power stations in the eastern Cape. The

study focused on De Hoek, Thyspunt and Tony’s Bay. The study included

structural mapping and diamond drilling.


Roux Offshore Geophysical Data 2011 Seafloor scarps, if tectonic, indicate possible displacements of 10 m (minor

faults in St Francis Bay), 22 m (Plettenberg Fault), and 52 m (Gamtoos Fault).

Yes Gamtoos Fault (8.4.3)

Plettenberg Fault (8.4.4)

Probability of activity, slip rate

GIS_S0084 MEMA/

KLH

Uenzelmann-

Neben et al.

Agulhas Plateau, SW Indian

Ocean: New Evidence for

Excessive Volcanism

1999 Uses seismic reflection lines to determine the structure of the Agulhas Plateau.

Abstract: A large number of extrusion centres were identified. Lava flows dip

away from those extrusion centres and form subparallel-stratified sequences.

We interpret those extrusion centres as the result of excessive volcanism in

course of the separation of the southern Agulhas Plateau from the Maud Rise.

Since the sedimentary layers appear to be little affected by the volcanism, that

episode obviously ceased before onset of sedimentation in Late Cretaceous

times. We have not found evidence for continental fragments within



255


Is The Data

Used in the

SSC Model?


overthickened, predominantly oceanic crust. We therefore propose that the

Agulhas Plateau belongs to the worldwide suite of Large Igneous Provinces of

predominantly oceanic origin.

Uenzelmann-

Neben et al.

Cenozoic Oceanic Circulation

Within the South African Gateway:

Indications from Seismic

Stratigraphy

2007 Discusses the exchange of water between the Indian and Atlantic Oceans off

the southern coast of Africa

Abstract: A compilation of the evolution of the oceanic circulation within the

South African gateway since the early Eocene on the basis of seismic

reflection data is put forward and discussed. The effect of a proto–Antarctic

Bottom Water (AABW) can be found in the southern Cape Basin and south of

South Africa as early as early Eocene–early Oligocene. In the period early

Oligocene–middle Miocene, a current equivalent to Antarctic Intermediate

Water/Agulhas Retroflection leaves its oldest traces identifiable on the eastern

Agulhas Plateau. Indications for the Benguela Current can be found in the

Cape Basin in middle Miocene times. With the onset of North Atlantic Deep

Water in the period middle Miocene–early Pliocene the branch of AABW

flowing through the Agulhas Passage is weakened and finally deflected to the

south in early Pliocene–Holocene times.


Wells &

Coppersmith

New Empirical Relationships

Among Magnitude, Rupture

Length, Rupture Width, Rupture

Area, and Surface Displacement

1994 Uses historical earthquakes to develop empirical relationships between

moment magnitude, surface rupture length, downdip rupture width, and

average surface displacement.



MEMA/

KLH

Wesnousky Displacement and Geometrical

Characteristics of Earthquake

Surface Ruptures: Issues and

Implications for Seismic-Hazard

Analysis and the Process of

Earthquake Rupture

2008 Uses statistics on about three dozen historical earthquakes to compare

observations of surface slip along strike.





256

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Table 3.8. Data Summary Table – Seismicity, Thyspunt PSHA.

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Seismicity

Albarello & d’Amico

Bulletin of the

Seismological

Society of America

91(4), 1694-1703

Detection of space and time

heterogeneity in the completeness

of a seismic catalog by a statistical

approach: an application to the

Italian area.

Keywords: catalogue completeness

2003 Statistical approach investigating statistical fluctuations in the spatial

and temporal distribution covered by a catalogue, illustrated on the

example of the Italian catalogue.

No The approach is assessed to be

a viable option for high-quality,

dense, long-span catalogues

such as the Italian catalogue

used in the study. However, it is

not deemed to be a viable

option for the Thyspunt

catalogue due to the very limited

number of data available, which

preclude a meaningful

interpretation of any statistically

detected heterogeneity.

AM & FS

Albini, P.

Report 2012-0099,

Rev.0, Council for

Geoscience,

Pretoria, South

Africa, 453 pp.

Investigating the past seismicity of

the Eastern Cape Province

Keywords: seismicity, Eastern Cape

2012 Provides an overview of the historical sources available for the Eastern

Cape region, and includes detailed individual studies including newly

assessed IDPs for 15 historical (pre-1900) and 15 early instrumental

(1900-1936) events that have occurred in the region.

Also includes seismic histories at 12 privileged observation points

within the region. Based on the assessment of positive and negative

evidence in the documents pertaining to these locations, the historical

record is assessed to be complete for the period ca. 1820-1936 for

MMI VI-VII.

Yes IDPs from individual studies

used in the determination of

source parameters for these

events.

Provides the primary source of

information for the completeness

assessment of the historical part

of the catalogue in the form of

seismic histories at 12

observation points.

AM & FS

Allen, T.I., Gibson,

G., Brown, A., &

Cull, J.P.

Tectonophysics 390,

5-24

Depth variation of seismic source

scaling relations: implications for

earthquake hazard in southeastern

Australia.

Keywords: seismic source scaling,

magnitude conversion

2004 Inversion of waveform data for 93 good-quality events that occurred in

southeastern Australia from 1993 to 2001 with ML 1.6 to ML 5.0.

Includes a locally derived ML-Mw relation: Mw = 0.64*ML +0.83. The

observed inconsistency between ML and Mw values is tentatively

related to the relatively high values of stress drop for southeastern

Australia.

Results used as an example of

ML-Mw relation from weak-

motion data and SCR regions,

where the slopes observed are

lower than 1.0 and generally of

the order of 0.67.

FS & AM


268

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Allen, T.I., Dhu, T.,

Cummins, P.R., &

Schneider, J.F. .

Bulletin of the

Seismological

Society of America

96(2), 572-585.

Empirical attenuation of ground-

motion spectral amplitudes in

southwestern Western Australia.

Keywords: Magnitude, weak motion

2006 Empirical relation between Mw and Mo from fitting waveform data from

southwestern Western Australia. The data is from 389 recordings of 69

events with Mw between 2.4 to 4.6 that occurred between 2001 and

2005.

The paper includes the following relation:

log10(M0) = 1.16 ML +10.34, which leads to an ML-Mw slope of

1.16/1.5 = 0.77.

Yes Results used as an example of




lower than 1.0 and generally of

the order of 0.67.

FS & AM

Alsaker, A. Kvamme,

L.B., R.A. Hansen,

Dahle, A. &,

Bungum, H.

Bulletin of the

Seismological

Society of America

81(2), 379-398.

The ML scale in Norway. 1991 The paper summarises the development of a locally calibrated local

magnitude scale for Norway. The authors also discuss the issue of

selecting an appropriate reference distance, which they set at 70 km

instead of the 100 km value originally proposed by Richter (1935).

Yes Used in the comparison of

regional attenuation functions.

The attenuation from this study

is very close to the results

obtained by Saunders et al.

(2012) once the difference in

reference distance has been

accounted for.s

FS & AM

Ambraseys, N.N. &

Adams, R.D

Natural Hazards 4,

389-419

Reappraisal of major African

earthquakes, south of 20°N, 1900-

1930

Keywords: Probability of detection,

seismicity, Africa

1991 Reappraised the macroseismic and instrumental data for a number of

larger events located south of 20°N that occurred in the time period

1900-1930. Only events with either macroseismic or instrumental

evidence pointing to a magnitude greater than 5¾ were included in the

study.

Provides background information regarding seismic recording and

likelihood of detection in sub-Saharan Africa during the first half of the

20th century.

The focus is mostly on events associated with East African Rift. The

analysis of the five southern African events appears to rely on the local

studies listed above, without collection of additional intensity data. The

study also includes reappraised instrumental magnitudes (MS) derived

from early instrumental phase readings and seismograms.

The following locations and magnitudes are given for the two events

Yes The background information is

considered in the determination

of the probabilities of detection

for the corresponding period.

Intensity information provided is

very limited and superseded by

the Albini (2012) study for the

two events (1912 Koffiefontein,

1920 Offshore) falling within the

catalogue study region.

Locations and magnitudes

proposed are reviewed in the

light of all the information

available for each event, which

includes data that was not

available to Ambraseys &

Adams.

AM & FS


269

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


falling within the catalogue study region:

1912-02-20 13:03 Fauresmith (Koffiefontein)

macroseismic epicentre 29.8S, 25.1

instrumental epicentre 29.5S, 25.0

[following Gutenberg & Richter (1956)]

…reappraised magnitude MS 6.2, dM=0.3, N=6

…MGR = 6.0, Imax VIII

1920-12-04 05:52 Offshore

macroseismic epicentre not available (offshore)

instrumental epicentre 39.0S, 23.5

[following ISS]

…reappraised magnitude MS 6.4, dM=0.2, N=4

…MGR = 6¼, Imax IV

A third event (31 October 1919,

Swaziland, MS 6.3) was

examined to check whether it

could fall within the catalogue

region, but it was concluded that

this event was a fake resulting

from the mix-up of phases from

two separate events occurring

on oceanic ridges either side of

southern Africa

The locations listed are used as

guidance but not considered

authoritative since additional

information was available for the

three events in question.

The reappraised instrumental

MS values for the 1912

Koffiefontein and 1920 offshore

events are adopted as they are

supported by the analysis of the

IDP data from Albini (2012).

Ambraseys, N.N. &

Adams, R.D.

Tectonophysics 209,

293-296

Reappraisal of major African

earthquakes, south of 20°N, 1900-

1930

Keywords: Early instrumental

seismicity, intensity data, African

seismicity

1992 Summary version of Ambraseys & Adams (1991), source parameters

presented are the same.

No Although more recent,

superseded by the more

detailed version presented in

Ambraseys & Adams (1991).

FS & AM

Ambraseys, N.N.,

Melville, C.P., &

Adams, R.D.

The Seismicity of Egypt, Arabia and

the Red Sea

1994 Detailed descriptive catalogue of historical and instrumental seismicity

for the region covered by northeastern Africa and the Arabian

peninsula.

Also includes some discussion of methodological aspects regarding

the calculation of source parameters from early instrumental data.

Yes Not directly relevant in view of

the distance of the geographic

region covered relative to the

region of interest. Used for

background information

regarding early instrumental

FS & AM


270

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


recording in Africa.

Also mentions the problems

encountered when using the

Sieberg (1932) compilation.

Bakun, W.H., &

Wentworth, C.M.

Bulletin of the

Seismological

Society of America

87(6), 1502-1521

Estimating earthquake location and

magnitude from seismic intensity

data.

Keywords: location, intensity,

magnitude

1997 The method estimates earthquake parameters (location and

magnitude) from seismic intensity data provided in the form .of an IDP

field.

The approach relies on the specification of an intensity prediction

equation (IPE) giving macroseismic intensity as a function of

magnitude and distance.

The paper presents the methodology, and illustrates it with an example

using Californian data.

Yes One of the methods used (as

implemented in the MEEP2

software) for the determination

of location and magnitudes of

the events for which IDP fields

are provided in the Albini (2012)

study.

FS & AM

Bakun, W.H. &

Scotti, O.

Geophysical Journal

International 164,

596-610.

Regional intensity attenuation

models for France and the

estimation of magnitude and

location of historical earthquakes.

Keywords: Intensity, IPE, ground-

motion prediction

2006 Development of regional intensity prediction equations for various

regions of France using the Bakun & Wentworth (1997) approach. This

results in two aggregated regional models (French SCR and Southern

France), with the former giving predictions close to Ambraseys (1985)

NW Europe model.

The French SCR IPE is given by:

IMSK = 4.48 + 1.27Mw – 3.37 log10(∆h)

where ∆h is the hypocentral distance.

Yes Provides the intensity prediction

equation used for the

determination of magnitudes

from intensity point data fields

using the Bakun & Wentworth

(1997) technique implemented

in the MEEP2 software.

Also used in the completeness

analysis to estimate the areas

over which an event could not

have occurred without being felt

with the threshold intensity of

MMI VI at the privileged

observation points of Albini

(2012).

AM & FS

Bakun, W.H.,

Gómez Capera, A.,

& Stucchi, M.

Bulletin of the

Seismological

Society of America

101(6), 2712-2725.

Epistemic uncertainty in the location

and magnitude of earthquakes in

Italy from macroseismic data.

Keywords: location, intensity

2011 Methodology to estimate the epistemic uncertainties related to the

determination of source parameters (location and magnitude) from

seismic intensity data using third-generation macroseismic intensity

analysis techniques.

The methodology combines results from three different analysis

techniques (Bakun & Wentworth, MEEP and BOXER) to obtain a

composite estimate of source parameters (location and magnitude)

and associated uncertainties. The uncertainties are derived from the

Yes All three methods are among the

four methods implemented in

the MEEP2 software. The

method presented by Bakun et

al. (2011) was adapted to use all

four methods implemented in

MEEP2 and to consider event-

specific method weights, since

FS & AM


271

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


composite probability density function obtained from a weighted

combination of the bootstrapped results from the individual methods.

The weights are method-specific and were obtained from a calibration

dataset.

review of the results involving

the IDP developer (Paola Albini)

revealed variable performance

of the methods depending on

the properties and imperfections

of the dataset.

Ballore, F. de

Montessus de

Seismic phenomena of the British

Empire

1896 Overview of known seismicity in the British Empire, including Africa as

a whole. Map indicates 17 known earthquakes for Cape Town, and 3 in

Natal. Text notes rarity of earthquakes at the Cape of Good Hope.

No Information provided insufficient

to identify individual events.

No dates or precise locations

provided.

AM & FS

Beauval, C.

PhD Thesis,

Universite Joseph

Fourier, Grenoble,

France

Analysis of uncertainties in

probabilistic seismic hazard

assessment: the example of

France.

Keywords: Catalogue processing,

probabilistic seismic hazard, France

2003 The thesis investigates the uncertainties involved in the development

of PSHA inputs.

In particular, it includes an overview of available techniques for

catalogue processing, illustrated with the example of France.

Yes Provided an overview of the

options available for the

Thyspunt catalogue analysis.

AM & FS

Beauval C., Yepes,

H., Bakun, W.H.,

Egred, J., Alvarado,

A., & Singaucho, J.-

C.

Geophysical Journal

International 181(3),

1613-1633.

Locations and magnitudes of

historical earthquakes in the Sierra

of Ecuador (1587–1996).

2010 Study determining locations and magnitudes of historical (pre-1976)

earthquakes in the Sierra region of Ecuador from intensity data, using

the Bakun & Wentworth (1997) technique.

No Provided an example application

of the Bakun & Wentworth

(1997) method, as well as

insights of the problems that can

be encountered when using

sparse datasets. Not used

directly as the example is from a

different geographic region and

tectonic environment.

AM & FS

Bethmann, F.,

Deichmann, N., &

Mai, P.M..

Bulletin of the

Seismological

Scaling relations of local magnitude

versus moment magnitude for

sequences of similar earthquakes in

Switzerland

2011 Explores the issue of ML-Mw scaling using empirical data from

Switzerland and theoretical considerations. Find that a slope of 1 is

well supported for Mw 3.0 to 5.0, but that this scaling breaks down at

smaller magnitudes, where the scaling is given by ML ~ 1.5 Mw.

Yes Used to support the imposed 1:1

ML-Mw scaling at larger

magnitudes, and to inform the

choice of the transition

magnitudes in the ML-Mw

scaling model.

AM & FS


272

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Society of America

101(2), 515-534.

Bondár, I., Myers,

S.C., Engdahl, E.R.,

& E. Bergman

Geophysical Journal

International 156,

483-496.

Epicentre accuracy based on

seismic network criteria.

Keywords: focal depth, location,

crustal phases

2004 The paper discusses location quality criteria, for which

recommendations are provided. For depth, the requirement is to have

at least one station within 30km epicentral distance.

Used to support the statement

that the South African

instrumental network can only

very rarely yield reliable depth

estimates using routine phases,

since the condition of having a

nearby station is rarely met by

events recorded by the SANSN.

AM & FS

Bowers, D.

Journal of

Geophysical

Research 102(B5),

9843-9857.

The October 30, 1994, seismic

disturbance in South Africa:

Earthquake or large rock burst?

Keywords: Focal mechanism, focal

depth, mining-related event

1997 Bowers (1997) used broad-band waveform data from the Global

Seismographic Network (GSN) stations to invert for moment tensor

and depth of the event. Inversion of the relative amplitudes of body and

surface waves at regional and teleseismic and polarities (for clear first

P onset) yielded a normal-type focal mechanism with strike=190°,

dip=45° and slip=-70°, and a scalar moment of 2.4E+16Nm. The fitting

of synthetic and observed seismograms gave the best result for the

depth of 2.3km.

Yes The full waveform method used

yield a normal type faulting and

a focal depth of 2.3km. Despite,

the reliable method used, the

result was not relevant to the

SSC model since the event is

mining related.

However, the paper provides

useful insights into the

limitations of depth

determination algorithms when

used in conjunction with sparse

data.

Although this is a mining-related

event, the focal mechanism

information was included in the

regional review since the event,

although mining-related, took

place in the form of slip on a

geological fault.

AM & FS

Brandt, M.B.C.

Report CGS 1997-

Implementation of the SEISAN

earthquake analysis software for

the SUN to analyze the data

1997 Report on the installation of the earthquake analysis program SEISAN

at CGS, including checks to ensure continuity of the practices followed

(in particular for magnitude determination). The paper shows good

Yes The program is used for routine

earthquake location at CGS,

including local magnitude

AM & FS


273

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


0263, Council for

Geoscience,

Pretoria, South

Africa

obtained through the South African

National Seismograph Network.

Keywords: earthquake analysis

continuity for a sample of values.

determination, hence the paper

was used to document the

practice followed for local

magnitude determination prior to

recalibration.

Brandt, M.B.C.

MSc Thesis,

University of Bergen.

A review of the reservoir induced

seismicity at the Katse Dam,

Kingdom of Lesotho, November

1995 to March 1999.

Keywords: induced seismicity, dam

2000 Location of microearthquakes induced by the Katse Dam in Lesotho.

The largest event had an ML of 3.0.

No Used to check the magnitudes

of .reservoir-induced events in

the Lesotho Highlands region,

which need to be removed from

the catalogue prior to recurrence

calculations.

AM & FS

Brandt, M.B.C.

Worshop

Presentation, TNSP

Workshop 1, April

2011.

Regional moment tensors, moment

magnitude, completeness and

national network expansion.

Keywords: Catalogue,

completeness analysis, SANSN

2011 Presentation about various aspects of the SANSN, focusing on recent

analyses using digital waveforms, as well as planned development.

In particular, the presentation included a completeness analysis of the

whole network.

Yes The magnitude of completeness

found using the maximum

curvature approach Mc ~ 1.9

corroborates the values found

from the analysis of the modern

instrumental subset of the

Thyspunt catalogue.

AM & FS

Brandt, M.B.C.,

Bejaichund, M.,

Kgaswane, E.M.,

Hattingh, E., & D.L.

Roblin

Seismological Series

37, Council for

Geoscience, South

Africa, 32 pp.

Seismic history of South Africa. 2005 The catalogue includes seismic events (historical and instrumental

data) in South Africa up to 1970, updating the Fernandez & Guzman

(1979) study, in particular updating it to include new events identified

from De Klerk & Read (1988). All magnitudes are given in terms of ML,

which are mostly obtained from conversions for larger events.

Applicability of and consistency between the conversion relations used

is not studied. A significant proportion of the events have ML values

determined from the epicentral intensity I0, and the intensity values

listed for events with instrumental magnitude determinations mostly

rely on the conversion relation being applied in reverse.

Yes Starting point for the pre-1970

portion of the catalogue.

Parameters were reviewed in

the light of additional information

gathered as part of the Thyspunt

project, as well as examination

of primary sources. Locations

were kept except where new

data allowed reappraisal. The

magnitudes listed were

systematically reappraised to

obtain uniform Mw values.

AM & FS

Brandt, M.B.C. &

Saunders, I.

New regional moment tensors in

South Africa

Keywords: South Africa, Moment

2011 Time domain surface wave waveform inversion technique was used to

derive moment tensor solutions, moment magnitude and focal depth

for 2 mine-related and 1 tectonic events. The mining events studied

Yes

The study provided local Mw

values used in the calibration of

the ML-Mw relation.

AM &FS


274

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Seismological

Research Letters

82(1), 69-80.

tensor, focal depth, tectonic event,

mining events, focal mechanism.

are: the 25th September 1997 Far West Rand and the 5th December

1998 Far West Rand earthquakes. The tectonic event studied is the

1999-02-04 Fauresmith earthquake, in the Koffiefontein area. This

latter event is located in the CK zone.

The focal depths from waveform fitting obtained were:

The 25th September 1997 Far West Rand event: 2km.

The 5th December 1998 Far West Rand event: 1km.

The 04th February 1999 Fauresmith event 11km.

The focal mechanisms derived from the moment tensor inversion were:

The 25th September 1997 Far West Rand event: normal-type faulting

(strike1=354°, dip1=49° and rake1=-86°, and strile2=167°, dip2=41°

and rake2=-95°). The seismic moment and moment magnitude

obtained were 1.55E+22dyne-cm and 4.1, respectively.

The 5th December 1998 Far West Rand event: normal-type with

strike1=296°, dip1=88° and rake1=144°, and strile2=28°, dip2=54° and

rake2=3°. The seismic moment and moment magnitude obtained were

1.36E+22dyne-cm and 4.1, respectively.

The 04th February 1999 Fauresmith event: normal-oblique type with

two nodal plane having (strike1=170°, dip1=70°, and rake1=-25°, and

strike2=269°, dip2=66° and rake2=-165°) . The first motion polarities

confirmed the moment tensor fault plane solution which gives the

following solution: strike=164°, dip=70° and rake=-53°. The seismic

moment and moment magnitude obtained were 5.60E+21dyne-cm and

3.8, respectively.

The focal depth and focal

mechanism solution for the

tectonic event were used for the

assessment of the future

earthquake characteristics in the

CK seismic source zone. These

data are among the few focal

depths available in the area. The

depth of the tectonic event is

11km.

The focal mechanism of the

tectonic event informs the style

of faulting in the CK source

zone for the future earthquake

characteristics. Beside the fact

that the focal plane solution was

obtained using moment tensor

inversion (good method and

relevant method), the solution is

among the few focal plane

solution available for South

Africa.

Brazier, R.A., Miao,

Q. Nyblade, A.A.,

Ayele, A., & C.A.

Langston

Bulletin of the

Seismological

Society of America

Local magnitude scale for the

Ethiopian Plateau.

2008 Study documenting the development of a local magnitude scale for the

Ethiopian Plateau. Used as an example of locally calibrated

attenutation function from Africa.

No Included in the comparison of

regional attenuation functions

from Africa and various SCR

regions.

FS&AM


275

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


98(5), 2341-2348.

Burton, P.W.,

McGonigle, R.,

Neilson, G., &

Musson, R.M.W.

Earthquake

Engineering in

Britain, Telford,

London, 91-110.

Macroseismic focal depth and

intensity attenuation for British

earthquakes

1985 Paper documenting a method to estimate earthquake depth using

macroseismic information. The method is the same as implemented in

the MACDEP software, which is described in Musson (1996).

Yes Method was tested using

MACDEP, however the data

was insufficient for conclusive

values of depth to be

determined. The tests showed,

however, that none of the

macroseismic data showed

indications of resulting from a

deeper event.

FS&AM

Chapman, C.H.,

Jen-Yi, C., & Lyness,

D.G.

In: Dornboos, D.J.

(ed.), Seismological

algorithms,

Academic Press,

London, p. 47-74.

The WKBJ seismogram algorithm. 1988 Ray-tracing program which computes synthetic seismogram. For

earthquake location, it helps with the identification of the additional

phases needed to improve location, and in particular depth

determination.

Yes Used in earthquake analysis

program SEISAN WKBJ

program help phases to

constrain focal depth.

AM & FS

Chow, R.A.C,

Fairhead, J.D.,

Henderson, N.B., &

Marshall, P.D.

Geophysical Journal

f the Royal

Astronomical Society

63, 735-745

Magnitude and Q determinations in

southern Africa using Lg wave

amplitudes.

1980 Regional study for magnitude relation and Q. Describes the

methodology used for the determination of the Bulawayo magnitude

MBUL. Comparison of the regional attenuation function with that of

Saunders et al. (2012) provides the basis for the ML* = MBUL relation

used in the magnitude uniformisation.

No Used in comparison of regional

attenuation functions as part of

the magnitude recalibration

exercise, and thus in the

magnitude conversion.

AM &FS

Crotwell, H.P.,

Owens, T.J., &

Ritsema, J. (1999).

Seismological

The TauP Toolkit: Flexible seismic

travel-time and ray-path utilities

1999 Describes the TauP software used to guide the identification of depth

phases for the depth determinations using the Ma & Atkinson (2006)

method.

Yes The software provides expected

arrival times for the various

seismic phases. These are then

compared to the observed

AM &FS


276

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Research Letters 70,

154-160.

arrival times.

Cua, G., Wald, D.J.,

Allen, T.I., Garcia,

D., Worden, C.B.,

Gerstenberger, M.,

Lin, K., & Marano, K.

GEM Technical

report 2010-4, 67pp.

“Best Practices” for using

macroseismic intensity and ground

motion intensity conversion

equations for hazard and loss

models in GEM1.

2010 Report providing an overview of available intensity prediction equations

(IPEs) available for various tectonic environments.

Yes Used to guide the selection of

the IPE adopted for the

determination of source

parameters from macroseismic

intensity.

AM & FS

De Klerk, W.J., &

Reed, J. du S.

Report, Albany

Museum,

Grahamstown,

South Africa.

An account of historical seismic

activity in southern Africa with

emphasis on the southern and

eastern Cape.

1988 Collection of newspaper clippings and a few additional documents

gleaned in the collections of the Cory Library in Grahamstown. Events

listed in this study were incorporated in the Brandt et al. (2005)

catalogue

Yes Used in the Albini (2012) study

and as a check on events that

were not included therein. Some

interpretation errors noticed for

dates (corrected).

AM & FS

Deichmann, N.

Bulletin of the

Seismological

Society of America

96(4A), 1267-1277.

Local magnitude, a moment

revisited.

2006 Provides theoretical background on the calculation of local magnitudes,

and argues that in principle, ML=Mw. over the whole range of seismic

moments for which ML can be determined. However, he notes that at

small magnitudes, deviations from this rule are often observed, due to

imperfections in the determination of ML.

Yes Used to support the imposed 1:1

ML-Mw scaling at larger

magnitudes, and explain the

deviations observed at small

magnitudes.

AM & FS

Drouet, S., Chevrot,

S., Cotton, F., &

Souriau, A.

Bulletin of the

Seismological

Society of America

98(1), 198-219.

Simultaneous inversion of source

spectra, attenuation parameters

and site responses: application to

the data of the French

accelerometric network.

2008 Describes the derivation of source parameters for France by inversion

of data from small-to-moderate events. In particular, this includes the

following ML-Mw relations:

Mw = -0.27(+/- 0.19) +0.95 (+/-0.05) MLDG

Mw = -0.02(+/- 0.17) +0.93 (+/-0.05) MReNaSS

Data comes from the Alps and Pyrenees regions, i.e. not from the

more active part of France rather than the French-SCR region.

Results used as an example of




lower than 1.0. MLDG tends to

take somewhat different values

from ML determinations in

neighbouring countries.

AM & FS


277

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Dziewonski, A. M.,

Ekström, G.,

Woodhouse, J.H. &

Zwart, G.

Physics of the Earth

and Planetary

Interiors 48, 5–17.

Centroid-moment tensor solutions

for October–December 1986

Keywords: Centroid moment tensor,

focal mechanism and focal depth

1987 In this paper, the Centroid moment tensor solution of the 1986-10-05

event in the SA-Lesotho border region is given. For the event, the

estimated centroid depth is 15km, the moment is 1.29E+17dyne-cm,

Mw is 5.3, the fault solution is pure normal fault with two nodal planes

having strike=168, dip=37 and rake=-90, and strike=348°, dip=53° and

rake =-90°. The seismic moment, moment magnitude and depth

obtained were 1.29E+17N-m, 5.3 and 15.0km, respectively.

Provides the Mw value of 5.3 for

the 1986-10-05 event. The focal

mechanism informs the style-of-

faulting in the CK region. The

depth value is less informative

as this is the fixed centroid

depth used by Harvard in CMT

solutions for shallow crustal

earthquakes.

AM & FS

Dziewonski, A. M.,

Ekström, G.,

Woodhouse, J.H. &

Zwart, G.

Physics of the Earth

and Planetary

Interiors 67, 211–

220.

Centroid-moment tensor solutions

for July–September 1990

Keywords: Centroid moment tensor,

focal mechanism and focal depth

1991 In this paper, the Centroid moment tensor solution of the 1990-09-26

mining event South Africa is listed. For the event, the estimated

centroid depth is 28.3km, the moment is 3.58E+16dyne-cm, Mw is 5.3,

the fault solution is pure normal oblique fault with two nodal planes

having strike=11, dip=45 and rake=-61, and strike=153°, dip=52° and

rake =-115°. The seismic moment, moment magnitude and depth

obtained were 3.58E+16N-m, Mw=5.0 and 28.3km, respectively.

Yes Information on depth is not used

since the event is not tectonic,

but it .provides a good example

of the algorithmic issues

encountered when leaving depth

unconstrained.

The focal mechanism was

included in the review of focal

mechanisms, since although

mining-related, the event

mechanism is consistent with

slippage on a geological fault

and hence includes information

about the regional stress field.

The Mw values was included in

the set of ML-Mw pairs from

mining events considered in the

development of the ML-Mw

conversion relation.

AM & FS

Ebel, J.

Seismological

Research Letters

80(6), 1062-1068.

Analysis of aftershock and

foreshock activity in stable

continental regions: Implications for

aftershock forecasting and the

hazard of strong earthquakes

2009 Determines Omori-law parameters for foreshock-aftershock sequences

in SCRs, covering multiple regions. The data include the Ceres

sequence and several other African earthquakes.

Finds that these parameters are in good agreement with each other, as

well as with the parameters determined for Southern California that are

No Illlustrates the fact that the

Omori law parameters needed

to calibrate the Reasenberg

(1985) algorithm are not likely to

be the source of the difficulty in

AM & FS


278

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Keywords: stable continental

region, foreshock, aftershock,

hazard

often used as default for the Reasenberg (1985) algorithm. Finds that

these parameters are in good agreement with each other, as well as

with the parameters determined for Southern California that are often

used as default for the Reasenberg (1985) algorithm.

calibration, as they appear to be

relatively stable from region to

region.

Edwards, B.,

Rietbrock, A.,

Bommer, J.J., &

Baptie, B. (2008).

Bulletin of the

Seismological

Society of America

98(4), 1915-1935.

The acquisition of source, path, and

site effects from microearthquake

recordings using Q tomography:

Application to the United Kingdom.

2008 Study determining source parameters for UK earthquakes based on

the inversion of weak-motion data. The paper includes the following

ML-Mw relation:

Mw = 0.71 ML +0.58





lower than 1.0, and generally

around 0.67.

AM & FS

EHB Bulletin

Online resource at

www.isc.ac.uk

Reanalysis of ISC data

Keywords: earthquake, location,

focal depth

Bulletin containing reanalysed parameters for events from the ISC

bulletin, using the methodology described in Engdahl et al. (1998).

The 1986-10-05 Matatiele earthquake was reanalysed and the depth

obtained was 11.7±0.7km.

The 1989-09-29 event located at the South Africa and Leshoto border

was also reanalysed. The solution gives a focal depth of 7.7km, for

which the uncertainty value is not provided.

Yes The depth values were included

in the compilation of South

African values considered in the

development of the depth

distribution.

Locations were reviewed where

available, but rarely provided the

best estimate since the

improvements to travel-time

curves work mostly for

teleseismic data and the

relaxation of the fixed depth

assumption worsens the quality

of the epicentral location in

cases such as this where the

constraints are not very strong.

AM & FS

Engdahl, E.R., Van

der Hilst, R., &

Buland, R.

Bulletin of the

Global teleseismic earthquake

relocation with improved travel

times and procedures for depth

determination.

1998 Reference documenting the reanalysis of events in the ISC bulletin to

generate the EHB bulletin,

using an improved travel-time model and allowing the depth to vary

freely.

Yes Although generally considered

superiorat the global scale to the

ISC locations because of the

reanalysis, this is one of the

cases where the EHB reanalysis

AM & FS


279

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Seismological

Society of America

88(3), 722-743.

does not really improve matters.

See discussion of EHB bulletin

for details.

Fairhead, J.D. &

Girdler, R.W.

Geophysical Journal

24(3), 271-301.

Seismicity of Africa

Keywords: Seismicity, Ceres and

Focal mechanism,

1971 In this study the fault plane solution of the Ceres earthquake is listed

among other solutions for events in Africa, mostly from the East African

Rift region.

To derive the fault plane solution, teleseismic first-motion polarities of P

and PKP phases were used. The solution obtained indicates a strike-

slip style-of-faulting with two nodal planes having the following strike

and dip: (1) 131° and 82°SW, and (2) 42° and 82°N. The plane (1) was

considered as the fault plane which coincides with the distribution (with

strike=120°) of the associated aftershocks associated (Green & Bloch,

1971). The event is located in the SYN zone.

Yes The method of first motion

polarity used is not very reliable

in general. But the information

on focal mechanism for this

Ceres event is consistent with

solutions obtained in the area.

This study was included in the

regional compilation of focal

mechanisms and used to inform

the style-of-faulting of the SYN

zone.

AM & FS

Fairhead, J.D. &

Stuart, G.W

Palmason, G.

(Editor), Continental

and Oceanic Rifts,

American

Geophysical Union

Geodynamic Series

8, 41–61.

The seismicity of the East African

rift system and comparison with

other continental rifts

Keywords: Earthquake, focal

mechanism, Koffiefontein,

1982 The focus of the paper is mainly on the East African Rift. The fault

plane solution of the 1st July 1976 Koffiefontein earthquake is

investigated among other African events. This event is located in the

CK zone.

First motion polarities of P phases were used to determine a fault plane

solution of normal-type characterized by E-W oriented tensional stress.

The two nodal planes obtained had the following values: (1) strike=2°

and dip=70° and (2) strike=18° and dip=20°.

Yes Results used to inform the style-

of-faulting assessment for the

CK zone.

AM & FS

Fan, G. & Wallace,

T.

Seismological

Research Letters

66(5), 13-18.

Focal mechanism of a recent event

in South Africa: A study using a

sparse very broadband network

Keywords: focal mechanism,

earthquakes, South Africa

1995 Focal mechanism of the October 30, 1994 event (mb = 5.7) near the

northwestern border of Orange Free State in South Africa is obtained

using waveform fitting. The depth of the event is 12km and the style of

fault is normal with strike=345, dip=14 and rake=-105. Although the

event was a mining event, the focal depth obtained is not consistent

with a mining related event (Bowers, 1997).

No The team did not use the

information on focal depth and

focal mechanism since the event

is not tectonic, and the

interpretation as such is

contradicted by observations in

the underground workings.

AM & FS

Fernández, L. M.

In: Van Wyk, W.L. &

Geophysical implication of the

1969-1971 Ceres seismic sequence

1974 Analysis of the 1969 Ceres mainshock and aftershock sequence using

local data. Only lists magnitude determinations, but no epicentral

coordinates. This information was included in the reappraisal the

Yes The Goetz Observatory (1972)

magnitude determinations are in

general preferred, as the

AM&FS


280

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


L.E. Kent (Eds). The

earthquake of 29

September 1969 in

the south-western

Cape Province,

South Africa.


4, Geological Survey

of South Africa,

Pretoria, South

Africa.

magnitudes of events in the Ceres sequence. The magnitudes are

listed as MS and Mb,, the former being in fact an ML value since it is

calculated from regional data.

Provides the ML value of 6.3 for the 1969 Ceres earthquake that is

used in the ML-Mw calibration checks. This value was derived using

the Rhodesian velocity tables of the time, which are very similar in

terms of attenuation to the recalibrated Saunders et al. (2012) results.

Therefore this value was considered directly equivalent to ML*,

similarly to early Bulawayo values.

analysis was based on a larger

number of recordings.

Fernández, L. M.

CGS Report 1993-

0038, Council for

Geoscience,

Pretoria, South

Africa.

The practice of evaluating local

Richter magnitude in South Africa.

1993 Summarises the early practices followed at CGS for the determination

of local magnitudes, since the inception of the SANSN. This effectively

covers ML determinations up to the introduction of SEISAN in 1997.

Yes Used in the recalibration of listed

ML values to be consistent with

the attenuation function

developed by Saunders et al.

(2012).

AM&FS

Fernández, L.M.. &

Guzmán, J.A.


10, Geological

Survey of South

Africa, 22pp.

Seismic history of Southern Africa.

Keywords: catalogue, intensity,

magnitude

1979 First catalogue systematically listing times, epicentral coordinates and

magnitudes for events in southern Africa up to 1970, covering South

Africa and neighbouring countries (Namibia, Botswana, Zimbabwe,

Mozambique). Reappraises previous South African studies as well as

including additional information gathered from archival records and

seismological sources. Wherever possible, epicentral locations are

given

Alternative instrumental magnitude determinations on other scales are

not included.

No Superseded by Brandt et al.

(2005) update. This version

used for checks.

FS & AM

Finsen, W.S.

Circular No. 110,

Union Observatory,

Johannesburg.

The geographical distribution of

some South African earthquakes.

Keywords: catalogue, magnitude

1950 Summary of the information gathered at the Union Observatory in

Johannesburg, predominantly based on macroseismic information

gathered from newspaper clippings or reports sent by members of the

public to the observatory. Some instrumental information included. Aso

includes a compilation of earthquake reports in historical sources.

Whenever possible provides coordinates for epicentral locations and

locations of intensity observations, but no magnitudes. The catalogue

incorporates the earlier study by Wood (1913).

Yes Included in the Fernandez &

Guzman (1979) and Brandt et

al. (2005) catalogues. The

original source was consulted to

in the review of source

parameters of the events

coming from this reference.

AM & FS


281

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Foster, A.N., and

Jackson, J.A

Geophysical Journal

International 134,

422-448.

Source parameters of Large African

earthquake: implications for crustal

rheology and regional kinematics

Keywords: Source parameters,

African earthquake, crustal

rheology

1995 Using analogue body-waveform data from the WWSSN stations and

digital data from the Global Digital Seismograph Network (GSN), P-

and SH-waves inversion and waveform fitting methods were used to

determine the focal mechanism, focal depth, moment tensor and

moment magnitude of the 29th September 1969 Ceres event. Two

pure strike-slip possible solutions were obtained: (1) strike=305°,

dip=87° and rake=3° and (2) strike=215°, dip=87° and rake=177°. A

seismic moment of 3.9E+18Nm, moment magnitude of Mw 6.4 and

depth of 5km were calculated.

Yes The focal depth and focal

mechanism obtained for this

event are of high quality since

the waveform inversion method

was used, and these information

was relevant since the event is

located in the SYN zone

AM & FS

Frankel, A.

Bulletin of the

Seismological

Society of America

84(2), 462-465.

Implications of felt area-magnitude

relations for earthquake scaling and

the average frequency of

perceptible ground motion

1994 Description of the methodology used in the determination of magnitude

in the MEEP method. The same approach is also used for the centroid

and pairwise methods. The method relies on relating the felt area

(isoseismal III) with physical properties of the source, which are region-

dependent.

Yes Used for the determination of

magnitudes for the MEEP,

centroid and pairwise methods

as implemented in the MEEP2

software. Calibration was done

in such a way as to be

consistent with the

macroseismic data available

from the instrumental period, as

well as the Bakun & Scotti

(2006) IPE.

FS & AM

Gane, P.G. & Oliver,

H.O.

Transactions of the

Geological Society

of South Africa 56,

21-33, Plates III-IV.

South African earthquakes - 1949

to December 1952

Keywords: catalogue,

completeness, detection

1953 Present the catalogue of events recorded by the Geological Survey

network 1949-1952, as well as a description of this network, including

instrument characteristics.

These data contribute to the completeness analysis through an

examination of the events successfully located by the network (e.g.

northern Botswana event of 1952, for which the South African network

location and magnitudes are very close to the teleseismic

determinations), as well as those for which the South African

recordings on their own are inconclusive.



al. (2005) catalogues. The

information regarding reporting

stations (checked against the

corresponding bulletins) was

used to recalibrate the ML

values provided in a manner

consistent with the Saunders et

al. (2012) attenuation function.

This information is also used in

the assessment of the

probabilities of detection for the

FS & AM


282

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


relevant period.

Gardner, J.K. &

Knopoff, L.

Bulletin of the

Seismological

Society of the

America 64(9),

1363-1367.

Is the sequence of earthquakes in

Southern California, with

aftershocks removed, Poissonian?

Keywords: Aftershocks,

declustering, catalogue

1974 Window-based declustering algorithm originally developed for

Southern California.

Long-established and widely-used declustering method, shown to

produce good results for many regions, as well as global catalogues.

Shown to provide similar results to rate-thinning approaches for sparse

catalogues (e.g. CEUS SSC)

Yes Examination of individual

clusters and overall performance

with Thyspunt catalogue shows

a good performance of this

algorithm, which is therefore

adopted for declustering.

FS & AM

Gasperini, P.,

Bernardini, F.,

Valensise, G., &

Boschi, E.

Bulletin of the

Seismological

Society of America

89(1), 94-110.

Defining seismogenic sources from

historical earthquakes felt reports

Keywords: intensity, location

1999 Determination of earthquake parameter based on spatial distribution of

IDPs. The method is a barycentre method that relies on the three

highest levels of intensity.

The paper also includes some further refinements, such as

determination of finite-fault properties. These are not considered here

as the data available would be insufficient for calibration.

Yes Method used for location using

intensity data, in the form


software (centroid method).

FS & AM

Goertz-Allmann,

B.P., Edwards, B.,

Bethmann, F.,

Deichmann, N.,

Clinton, J., Fäh, D.,

& Giardini, D.

(2011).

Bulletin of the

Seismological

Society of America

101(6), 3088-3095.

A new empirical magnitude scaling

relation for Switzerland.

2011 This paper describes the development of a new ML-Mw scale for

Switzerland, using Mw values determined through a variety of

methods. Due to a breakdown of the ML ~ Mw scaling relationship at

low magnitudes, the relation has three branches (linear,

quadratic,linear):

ML < 2 Mw = 0.594 ML + 0.985

2 ≤ ML ≤ 4 Mw = 1.327 + 0.253 ML + 0.085 ML2

ML > 4 Mw = ML -0.3

Yes This study provides the basic

form of the ML-Mw relation

developed. The main difference

with the Thyspunt case is that

there is Swiss data to constrain

the quadratic transition, whereas

in the South African case there

is onl data to control the linear

segments.

FS & AM

Goetz Observatory

Technical Report,

Goetz Observatory,

A seismological study of

earthquakes in the southwest Cape

Province 1969-1970.

1972 This study, compiled by the Goetz Observatory in Bulawayo

(Zimbabwe), is the authoritative local reference for source parameters

of the Ceres sequence, as it includes a very careful review of all

available recordings from South Africa, Namibia and Zimbabwe. Origin

Yes Used for source parameters of

the Ceres sequence, and to

inform source parameter

reappraisal as well as probability

AM & FS


283

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Meteorological

Department,

Bulawayo, February

1972, 24pp.

Keywords: catalogue, magnitude,

Ceres

times and magnitudes are provided for all events studied, alongside

epicentral coordinates whenever these could be determined.

The study also provides minimum values of magnitude that could be

determined using Zimbabwean records. It also comments on the

quality of the NEIC determinations, which are found to be poorer than

those from local data, in particular due to biases introduced by

recordings at the Pretoria station.

of detection asssessments.

Green, W.E. &

McGarr, A.

Bulletin of the

Seismological

Society of America

62(3), 869-871.

A comparison of the focal

mechanism and aftershock

distribution of the Ceres, South

Africa earthquake of September 29,

1969

Keywords: focal mechanism,

aftershocks, Ceres

1972 The fault plane solution was determined from the first motion P-wave

polarities of long-period seismograms of the Ceres (1969-09-29)

recorded by 42 World-Wide Standardized Seismographic Network

(WWSSN) stations. The derived focal mechanism showed that the

nodal plane identified as fault plane was of strike N 39 ° W to N 43° W,

associated with a pure strike-slip mechanism.

The information on focal mechanism is relevant since the event was

located in the SYN zone.

Yes The use of first-motion polarities

only limits the quality of the focal

mechanism solution, which is

however broadly consistent with

the seismicity observed during

the aftershock sequence. This

informatiom was used to inform

future earthquake characteristics

in the SYN zone.

AM & FS

Green, W.E. & Bloch

S.

Bulletin of the

Seismological

Society of America

61(4), 851-859.

The Ceres, South Africa earthquake

of September 29, 1969. I. Report on

some aftershocks.

Keywords: duplex, imbricates,

tectonic events

2004 Using the temporary local network after the September 29, 1969 Ceres

earthquake, aftershocks were recorded and located. Most events were

located in the Ceres region.

The solution yields a maximum aftershock depth of 9 km with most

aftershocks prior to 1970-04-14 event (the main aftershock) shallower

than 6.5 km.

The paper also provides the best-constrained epicentral coordinates

for the Ceres mainshock and two larger aftershocks.

Yes The quality of the information on

the type of faulting and depth is

very good since a very local

network was used for location.

Unfortunately, the coordinates of

the majority of the aftershocks

are only provided in graphical

form.

The locations for the three

identifiable events are the ones

included in the catalogue, since

these are the best-constrained

estimates. Note that the

coordinates listed in the text of

the paper had to be corrected to

obtain a location matching the

figure shown.

AM & FS

Greenhalgh, S.A., &

Parham, R.T.

The Richter earthquake magnitude

scale in Southern Australia.

Describes the development of a locally calibrated ML scale for

southern Australia. The corresponding attenuation function was

Yes Used for a comparison of

regional attenuation functions as

FS & AM


284

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


(1986).

Australian Journal of

Earth Sciences

33(4), 519-528.

included in the comparison of the newly derived locally calibrated

attenuation function of Saunders et al. (2012) with published

attenuation functions from other SCR regions.

part of the ML recalibration

exercise.

Grünthal, G.

Proceedings 3rd

International

Symposium on the

Analysis of

Seismicity and

Seismic Risk.

Czechoslovak

Academy of

Science, Prague, 19-

25.

The up-dated earthquake catalogue

for the German Democratic

Republic and adjacent areas—

Statistical data characteristics and

conclusions for hazard assessment

Keywords: catalogue, hazard

assessment

1985 Includes independently determined magnitude-dependent space and

time windows for window –based declustering developed for Central

Europe.

Windows are almost identical to the Gardner & Knopoff (1974)

windows and in consequence declustering results are extremely

similar.

No Not used as an alternative

declustering approach given the

assessment that this would not

really be a genuine alternative

(same type of approach, i.e.

window-based, and identical

imported calibration).

Reliance nevertheless high as

results strongly support

universal/transportable nature of

Gardner & Knopoff (1974)

windows.

FS & AM

Grünthal, G.,

Wahlströhm, R., &

Stromeyer, D.

Journal of

Seismology 13(4),

517-541.

The unified catalogue of

earthquakes in central, northern,

and northwestern Europe (CENEC)

– updated and expanded to the last

millenium.

2009 Describes the development of a seismicity catalogue for central,

northern, and northwestern Europe, and includes the following ML-Mw

relation:

Mw = 0.0376 ML2 +0.646 ML + 0.53

Also includes a lot of discussion on the issue of magnitude

uniformisation, flagging up differences in ML determination practices in

various countries, which can lead to discrepancies between magnitude

estimates for the same event by agenciesfrom neighbouring countries.

Yes Supports the quadratic form of

the transition in the ML-Mw

calibration.

More generally, used in the

review of ML-Mw relations from

similar tectonic environments

and/or underlying datasets

FS & AM

Gutenberg, B., &

Richter, C.F.

Princeton University

Press.

Seismicity of the Earth and

associated phenomena.

1956 Global catalogue of seismicity based on reanalysis of the ISS/BAAS

bulletin data, for which locations are reappraised and MGR

magnitudes. Includes three events of interest: 1912-02-20 Koffiefontein

(MGR = 6.0), 1920-12-04 Offshore (MGR = 6¼), and 1932-12-31 Off

Cape St Lucia (MGR 6¾).

For 1912-02-20 13:03 Fauresmith (Koffiefontein), the instrumental

epicentre 29.5S, 25.0 is adopted.

For the 1920-12-04 Offshore event, the ISS epicentre (39.0S, 23.5E) is

preferred to Gutenberg & Richter’s solution (39.0S, 21.0E) as it is more

consistent with both macroseismic data and the instrumental recording

at Cape Town.

Yes Parameters for 1912 and 1920

events reviewed by Ambraseys

& Adams (1991).

Details of MGR calculation have

remained unknown, generally

considered to be equivalent to

MS or MS – 0.2. For 1912 and

1920, values superseded by MS

values recalculated by

Ambraseys & Adams (1991).; for

1932 the value was reviewed in

FS & AM


285

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


For the 1932-12-31 event, the location is almost identical with the ISS

location, but the magnitude is higher than that suggested by the

macroseismic data.

the light of the magnitudes

determined for intensity data.

Hainzl, S.,

Scherbaum, F., &

Beauval, C.

Bulletin of the

Seismological

Society of the

America 96(1), 313-

320.

Estimating background activity

based on interevent-time

distribution

Keywords: main hock, aftershock,

classification,

2006 Stochastic point-process simulations to classify events as main shocks

or aftershock and obtain non-parametric estimates of the background

seismicity rate based on the inter-event time distribution.

The method is not conditioned on magnitude, therefore the event

designated as main shock in a cluster is not necessarily the largest of

the cluster. While this does not affect the performance of the method

when applied to large datasets, this characteristic is likely to lead to

issues in the case of a very sparse catalogue as considered here.

Additionally, the method subdivides the data in subsets (magnitude

bins). Given the very limited number of data points in the catalogue

under consideration, this subdivision process hampers the

determination of stable estimates.

No Method cannot be applied here

due to data limitations (dataset

is too small to allow subdivisions

that would satisfy stability

criteria); the assessment of the

method itself as high-quality is

not affected.

FS & AM

Hanks, T., &

Kanamori, H.

Journal of

Geophysical

Research 84, 2348–

2350.

A moment magnitude scale. 1979 Paper defining the moment magnitude scale. The original definition is

used throughout for conversions between seismic moment and

moment magnitude.

Yes Note that all moment

magnitudes obtained from the

original definitions are noted Mw

in the catalogue work and are

thus identical to the M of some

authors.

AM & FS

Henderson, N.B.

Rhodesian

Meteorological

Service,

Meteorological

Notes, Series A, No.

42.

Earthquake magnitude

determination based on short

period crustal waves.

1974 Reference for the local travel-time tables used by the Bulawayo

network prior to recalibration for alignment with the NEIC mb values,

reproduced in Chow et al. (1980). This provides information about the

determination of the MBUL values in the catalogue (from the 1960s

and 1970s), and the basis for the conversion adopted for these values.

Yes Used to support the equivalence

between MBUL and ML* (South

African ML

AM & FS

Hutton, L.K., &

Boore, D.M.

The ML scale in Southern

California.

1987 Reformulation of the original definition of local magnitude by Richter

(1935) to use a reference distance of 17 km instead of the 100 km

reference distance originally proposed.

Yes Used to recalibrate the ML

values calculated using SEISAN

to be consistent with the new

AM & FS


286

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Bulletin of the

Seismological

Society of America

77(6), 2074-2094.

This formulation is the default formulation implemented in SEISAN and

was used for the routine determination of ML in South Africa from 1997

onwards.

local calibration of Saunders et

al. (2012).

IASPEI

Dated 9 September

2011. URL:

www.iaspei.org./com

missions/CSOI/Sum

mary_WG-

Recommendations_

20110909.pdf [last

accessed March

2012].

Summary of Magnitude Working

Group recommendations on

standard procedures for

determining earthquake magnitudes

from digital data.

2011 Document summarizing the IASPEI recommendations regarding

magnitude determinations, which provides guidelines for current best

practice, as well as some insights into historical practices. Includes a

section about local magnitude, which explicitly allows deviations from

the original definition such as the use of vertical amplitudes.

Yes Used in the assessment of the

quality and consistency of the

instrumental magnitudes

available, many of which are

from the 1960s and 1970s when

determination practices were still

quite variable.

AM & FS

Jensen, B.L.

MSc Thesis,

Memphis State

University.

Source parameters and

seismotectonics of three

earthquakes in the stable

continental interior of Africa

Keywords: source parameters,

seismotectonics, stable continental

region, microstructures, tectonic

transport,

1991 Using waveform inversion and modelling of long period P- and SH-

waves, the focal mechanism, focal depth, seismic moment and

moment magnitude of the 01-07-1976 Koffiefontein earthquake are

determined. The result of the inversion showed that the mechanism

was a pure normal fault with strike=308°, dip=22° and rake=-86°. The

focal depth, seismic moment and moment magnitude were 5.5km,

2.66E+24 dyne-cm and 5.8 respectively.

The event was located in the CK zone.

Yes Provides the Mw value of 5.8 for

the 1976 Koffiefontein event.

Depth value included in the

dataset considered as part of

the development of the depth

distribution. Focal mechanism

informed the style-of-faulting for

the CK zone.

AM & FS

Johnston, A.C.,

Coppersmith, K.J.,

Kanter, L.R., & C.A.

Cornell

Final Report

submitted to Electric

Power Research

Institute (EPRI).

The Earthquakes of Stable

Continental Regions

Keywords: earthquakes, stable

continental region, seismic source

1994 Compilation of a catalogue of earthquakes having occurred in Stable

Continental Regions (SCRs) and analysis of their source

characteristics. Also includes discussion of some methodological

issues, including uniformisation of magnitudes (further developed in the

Johnston 1996a, 1996b papers) and assessment of catalogue

completeness.

In particular, presents the method involving equivalent periods of

completeness (based on probability of detection) implemented in

EPRI94 and later in the CEUS SSC study.

No Catalogue listings cross-

checked with available

information.

Magnitude conversion relations

reviewed, but not used directly

as they were superseded by

those in the Johnston (1996a,

1996b) papers.

Provides the methodological

basis for recurrence calculations

FS & AM


287

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


using equivalent periods of

completeness (simplified in the

Thyspunt study to avoid

subdivision of already very

limited datasets).

The regional completeness

periods for Africa and Antarctica

were considered alongside other

information in the assessment of

the probabilities of detection.

Johnston, A.C.

Geophysical Journal

International 124,

381-414.

Seismic moment assessment of

earthquakes in stable continental

regions – I. Instrumental seismicity.

1996a Summarises magnitude conversion relations developed for SCR

environments, which are updates of those presented in Johnston et al.

(1994). Used to inform selection of conversions for uniformisation of

magnitudes.

Superseded the Johnston et al.

(1994) relations. Used for

conversion from mb..

FS & AM

Johnston, A.C.

Geophysical Journal

International 125,

639-678.

Seismic moment assessment of

earthquakes in stable continental

regions – II. Historical seismicity.

1996b Summarises methodological aspects and equations to obtain

magnitude values from macroseismic intensity data. The equations

include equations for areas corresponding to individual intensity levels,

which are used alongside local data to guide the calibration of the

macroseismic intensity analysis methods implemented in MEEP2.

The equations are updates of those presented in Johnston et al.

(1994), and can be considered mutually consistent as they are

developed from a single dataset. The paper also includes an example

application to the 1969 Ceres earthquake.

Used for magnitude

determinations from Imax and

isoseismals, and to guide the

calibration of the macroseismic

analysis methods implemented

in the MEEP2 software.

FS & AM

Kim, W. Y.,

Wahlström, R., &

Uski, M.

Tectonophysics

166(1-3), 151-161.

Regional spectral scaling relations

of source parameters for

earthquakes in the Baltic shield.

1989 Determination of source spectra through Fourier inversion of small-to-

moderate earthquakes from the Fennoscandian shield. Find the

following relation:

Log(M0) = 16.93 + 1.01 ML

This results in a Mw:ML scaling ratio of 1.01/1.5 ~ 0.67.





lower than 1.0, and generally

around 0.67.

FS & AM

Knopoff, L. &

Gardner, G.K.

Geophysical Journal

28, 311-313.

Higher seismic activity during local

night on the raw worldwide

earthquake catalog

Keywords: seismicity, catalogue

1972 Study of statistics of seismicity leading to Gardner & Knopoff (1974)

study.

No Study superseded by Gardner &

Knopoff (1974)

FS & AM


288

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Geophysical Journal

28, 311-313.

Kövesligethy, R. von

Gerlands Beiträge

zur Geophysik 8,

363-366.

Seismischer Stärkegrad und

Intensität der Beben.

1907 Provides the original formula used to describe the attenuation of

intensity with distance implemented in the MEEP methodology to

control the spacing of isoseismals. The same formula can be used to

determine macroseismic depth.

Yes Used via its implementation in

the MEEP2 and MACDEP

software.

FS & AM

Krige, L.J

Transactions of the

Geological Society

of South Africa 39,

429-40.

The Swaziland and Fauresmith

Earthquakes of January 1936.

1936 Monograph summarising instrumental and macroseismic information

about the 1936-01-12 Swaziland (outside the catalogue region) and

1936-01-16 Fauresmith (Koffiefontein region of CK zone) events.

Used to reappraise the source parameters of the 1936-01-16

Fauresmith event.

Yes Included in Finsen (1950),

Fernandez & Guzman (1979)

and Brandt et al. (2005)

catalogues.

Not included in Midzi et al.

(2012) isoseismal data for

calibration of intensity methods

as there are no independent

instrumental estimates.

FS & AM

Krige, L.J, & Maree,

B.D.

Bulletin No. 20,

Geological Survey of

South Africa, 14pp

[first published in

Afrikaans, 1948].

Earthquakes in South Africa. 1951 Krige & Maree (1951) compilation of individual studies of 11 events

having occurred in South Africa between 1938 and 1944.

Used to reappraise the source parameters of the events listed falling

within the catalogue region.

Yes Included in Finsen (1950),

Fernandez & Guzman (1979)

and Brandt et al. (2005)

catalogues.

FS & AM

Krige, L.J., & Venter,

F.A.

Transactions of the

Geological Society

of South Africa 36,

101-112.

The Zululand Earthquake of the

31st December 1932.

1933 Monograph about the 1932-12-31 Off Cape St Lucia earthquake,

containing both macroseismic and instrumental information.

Used for the reappraisal of source parameters for this event.

Yes Included in, and superseded by,

individual event study in Albini

(2012) in terms of macroseismic

data.

FS & AM

Krüger, F.,

Reichman, S., &

Scherbaum, F.

Moment tensor solution for the

29.9.1969 Ceres earthquake.

2011 In this investigation of the Ceres earthquake, moment tensor inversion

was done using scanned and digitized seismograms from a set of

WWSSN stations operational in 1969. For the estimate of the solution,

Yes Provides the best estimate Mw

magnitude (6.2) for the Ceres

event. The uncertainty of 0.2

AM & FS


289

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


SSHAC Level 3

Workshop 1, Cape

Town.

Keywords: moment tensor, Ceres

earthquake

body- and surface waves were used. The best double solution

obtained yielded a strike-slip (SSE-WNW) fault with strike=305°,

dip=78° and rake=1.2°, with a centroid depth=15km. The moment

magnitude was determined to be Mw = 6.2 +/- 0.2 Examination of the

waveforms indicated the absence of depth phases, pointing to a depth

shallower than 20 km for the Ceres event.

magnitude units encompasses

other Mw values proposed for

this event.

The focal mechanism obtained

was rated high quality and used

to inform the style-of-faulting

assessed for the SYN source

zone as part of the future

earthquake characteristics in

this zone.

The observation regarding depth

phases was used to inform the


distribution adopted.

Langston, C.A.,

Brazier, R., Nyblade,

A.A., & Owens, T.J.

Bulletin of the

Seismological

Society of America

88(3), 712-721.

Local magnitude scale and

seismicity rate for Tanzania, East

Africa.

1998 Study documenting the development of a local magnitude scale for

Tanzania. The corresponding attenuation function was used in the

comparison of the attenuation function determined by Saunders et al.

(2012) with other attenuation functions in sub-Saharan Africa.

Used in comparison of regional

attenuation considered as part

of ML recalibration.

FS & AM

Luen, B. & Stark,

P.B.

Geophysical Journal

International 189,

691-700.

Poisson tests of declustered

catalogues

Keywords: catalogue, declustering

2012 Statistical study using Southern Californian catalogue. The authors

investigate the performance of various declustering techniques in

terms of producing a spatially inhomogeneous, temporally

homogeneous Poisson process (SITHP).

The authors find that none of the techniques examined (including

Gardner & Knopoff, 1974 and Reasenberg, 1985) satisfy this

hypothesis. Previous results to the contrary are attributed to

deficiencies in the statistical tests used.

Results are somewhat improved by relaxing the statistical criterion and

replacing it by one of “conditionally exchangeable times”.

Yes

(indirectly)

The dependence on the

conclusion of this article is low

despite an undoubtedly very

rigorous mathematical analysis,

because the authors of the

paper do not seem to consider

the practical aspects of the

application (and by their own

admission are unfamiliar with

the actual objectives of

catalogue declustering). As a

result, many of the points

highlighted as statistical

FS & AM


290

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


weaknesses are in fact

properties desirable in seismic

hazard applications (e.g., a

relative insensitivity to

fluctuations in the long-term

rate, as well as to short-term

fluctuations on the order of

weeks). The Poissonian process

providing their null hypothesis,

which places a strong emphasis

on spatial correlations, also

bears little resemblance to the

model used in seismic hazard

analysis , which focuses

essentially on the temporal

distribution of events within a

zone, regardless of their location

within the zone, the spatial

windows in declustering

algorithms mainly serving the

purpose of avoiding

misassociation of independent

events overlapping in time when

larger zones are considered.

While there is no reliance on the

conclusions of the study, the raw

data presented informs the

assessment of the comparison

of the Gardner & Knopoff (1974)

and Reasenberg (1985)

techniques by providing a

second application example in

addition to Van Stiphout et al.

(2012).

Ma, S., & Atkinson, Focal depths for small to moderate 2006 Method to determine focal depth of regional earthquakes Yes The method was used to AM & FS


291

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


G.M.

Bulletin of the

Seismological

Society of America

96(2), 609-623.

earthquakes (mN ≥2.8) in Western

Quebec, Southern Ontario, and

Northern New York

Keywords: focal depth, regional

events, depth phases

using travel time differences between sPg, sPmP and sPn, and their

respective corresponding phases Pg, PmP and Pn. These travel-time

differences are less sensitive to epicentral distance than to depth, and

increase linearly with depth. Focal depth can be thus be de-coupled

from the epicentral solution and obtained through a waveform fitting

method. Ma & Atkinson (2006) applied this method to a set of Eastern

North American events, and found that a single station can be

sufficient to constrain the event depth, as long as the depth phases can

be read clearly. The latter is a function of the source-to-site distance,

with sPg typically well developed at distances of up to ~100 km, sPmP

typically well developed in the range 200-300 km, and sPn sometimes

being observable for the larger events of the dataset. The method is

most commonly applied with the PmP phase, since the sensitivity of

the results to shallow structure (velocity and attenuation) has been

found to be smaller for this phase. Also, Ma & Atkinson (2006) showed

that for the Canadian Shield, the waveforms are quite simple for

distances between 1.8° to 2.8° and 4.1° to 4.8°. At those distances,

sPg and Pg disappear and the first phase is a very weak Pn, followed

by PmP and sPmP.

determine 9 additional focal

depth values based on the

sPmP phase, using recordings

from the South African Seismic

Experiment (SASE). This

contributed to the development

of the depth distribution

adopted.

Ma, S., & Eaton,

D.W.

. Geophysical

Journal International

185, 871-889. 223

Combining double-difference

relocation with regional depth-

phase modelling to improve

hypocentre accuracy

2011 Extension of the Ma & Atkinson (2006) method. The method presented

here computes focal depth using regional depth phases and relocate

earthquake using a modified double difference method where depth

previously is fixed.

No The method could not be used

for the Thyspunt project as it

needs a good azimuthal

coverage and more recording

stations than were available.

AM & FS

Maasha, N. &

Molnar, P.

Journal of

Geophysical

Research 77(29),

5731-5743.

Earthquake fault parameters and

tectonics in Africa

Keywords: source parameters,

earthquake, Africa

1972 Provides fault plane solutions of 11 earthquakes in Africa, including the

1969 Ceres earthquake, for which a strike-slip style-of-faulting is

indicated.

The mechanism and seismic moment were determined using first

motions polarities, and P-wave spectra, respectively. For P-wave

spectra, the Brune model (Brune, 1970) was used for the calculation of

seismic moment and moment magnitude. The result showed that the

Ceres event mechanism was strike-slip type with two nodal planes: (1)

Yes The method used is not the best

since only first-motion polarities

were used for the mechanism,

and only P-waves were used in

the magnitude determination.

However, the solution is

consistent with others developed

for this event, hence this

information was used to inform

AM & FS


292

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


strike=44° and dip=82° and (2) strike=133° and dip 81°. Seismic

moment of 2.0E+25 dynes-cm and moment magnitude of Mw 6.4 was

calculated.

the style-of-fauting in the SYN

source zone, as well as the

determination of the Mw value

for Ceres and its uncertainty.

Maclear, T.

South African

Commercial

Advertiser, 24th

November 1835

Letter to the editor 1835 Letter from the Astronomer Royal based at the Cape of Good Hope

Observatory, describing a Cape Town earthquake that occurred on 11

November 1835.

Yes The earthquake described had

already been included in the

Brandt et al. (2005) catalogue.

This document mainly

contributes to the assessment of

the probability of detection

values assigned to the region

surrounding Cape Town, as an

early example of earthquake

monitoring by a scientific

institution.

AM & FS

Mangongolo A.

CGS Unpublished

investigation

Focal mechanism data 2012 In an effort to extend the limited dataset of focal plane solutions, six

events were investigated using the waveform data from the SASE

temporary array: the 1998-04-24 Augrabies event in the NAM zone

(Event 1), the 1998-06-22 Three Sister event in the KAR zone (Event

2), the 1998-09-06 Lesotho earthquake in the CK zone (Event 3), the

1998-10-05 Fraserberg event in the CAR zone (Event 4), the 1999-02-

04 Koffiefontein event in the CK zone (Event 5) and the 1999-07-03

Koffiefontein event in the CK zone (Event 6).

Event 1:

The 24th April 1998 Augrabies earthquake was located at 28.214°S

and 20.367°E. To derive the focal mechanism, first-motion P-wave

polarities from the SASE stations were used. Using FOCMEC, the

solution obtained is strike=138°, dip=90° and rake=38°. While FPFIT

gives the following solution: strike=132°, dip=80° and rake=18°. Both

solutions obtained yield a strike-slip fault-type. The solution was of

relevant since the solution is amongst the few we have for event in the

NAM zone.

Event 2:

Yes The solutions obtained were not

of excellent quality since only

polarities were used and the

azimuthal coverage was not

good for some events.

Event 1 was used for the future


NAM seismic zone.

Event 2 and 4 were used for the


in the KAR seismic zone.

Event 3, 5 and 6 located in the

CK zone were used for the


in the CK zone.

AM & FS


293

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


This event was located at the coordinate 31.877°S 23.356°E. To derive

the focal solution, first-motion P-wave polarities from the SASE

stations, were used The fault-type mechanism shows an oblique-slip

with strike=19°, dip=41° and rake=-121°. This solution is poor since

most of the stations used are situated north of the event.

The quality for this solution is not very good since only polarities were

used and the azimuthal coverage was not the best. But the solution

was of good relevance since the solution is amongst the few we have

for event in the KAR zone.

Event 3:

The location of this event is at the coordinate 30.255°S and 27.976°E.

First-motion P-wave polarities of waveforms recorded at the SASE

stations, were used to obtain the focal mechanism solution for this

event. The fault-type mechanism shows a normal-type fault with

strike=148°, dip=48° and rake=-67°. The solution also looks poor since

only stations located north of the event were used for the fault plane

solution. Although the quality is not very good, the relevance is good

since the event is located in the CK zone and the mechanism is

consistent with other mechanisms in the Lesotho area.

Event 4:

The 5th October 1998 Fraserburg earthquake was located at 30.972°S

and 22.347°E. First-motion P-wave polarities as recorded at SASE

stations were used to derive the focal mechanism solution. Two

computer programs, FOCMEC and FPFIT were used to determine the

solution. Using FOCMEC, the solution obtained was strike=9°, dip=67°

and rake=-19°, while FPFIT gives the following solution: strike=345°,

dip=76° and rake=-26°. Both solutions obtained yield a strike-slip fault-

type.

The quality was not very good since only polarity data were used. But

the information was relevant because this solution is among the few

solutions we have in the CAR zone.

Event 5:

The 4th February 1999 Fauresmith earthquake belongs to the

Koffiefontein earthquake cluster and was located at 29.76°S and

25.70°E.


294

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


First-motion P-wave polarities as recorded at SASE stations were used

to derive the focal mechanism solution. The solution obtained was

strike=98°, dip=78° and rake=-121°. This solution obtained yield a

normal-oblique fault-type.

The quality was not very good since only polarity data were used.

Although the quality is poor, the relevance was high since the solution

is among the few solutions we have in the CK zone.

Event 6:

This event belongs to the Koffiefontein earthquake cluster and was

located at 29.501°S and 25.171°E.

First-motion P-wave polarities as recorded at SASE stations were used

to derive the focal mechanism solution. The solution obtained was

strike=68°, dip=58° and rake=-174°. This solution obtained yield a


The quality was not very good since only polarity data were used, but

the relevance was good because this solution is among the few

solutions we have in the CK zone.

Mangongolo A.

CGS Unpublished

investigation

Focal depth This was an effort to obtain more focal depth using the regional depth

phases method (RDPM) after Ma & Atkinson (2006). The regional

depth phases used is the sPmP or the S-wave that travels upward to

the surface, converts to a P-wave, then reflect at the Moho and travels

upward to the station and the PmP phase associated. Using known

focal mechanism solutions, focal depths are obtained through

waveform fitting method.

In the investigation, 9 events were used which occurred in South Africa

and recorded by the SASE temporary array. The depth for the 9 events

are:

7.3±2.3 km for 1998-04-24 Augrabies event located in the NAM zone

6.3±0.3 km for the 1998-06-22 Three Sisters events located in the

CAR zone

14.8±1.5 km for the 1998-07-05 Lesotho event located in the CK zone

18.6±3.0 km for the 1998-09-06 Lesotho in the CK zone.

5.6±0.3 km for the 1998-10-05 Fraserburg event located in the KAR

Yes The team used this information

to determine the range of

seismogenic focal depths to be

considered in the SSC model.

AM & FS


295

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


zone

6.3±0.9 km for the 1999-01-07 Koffiefontein event located in the CK

zone.

8.1±1.5 km for the 1999-02-04 Koffeifontein event located in the CK

zone.

7.5±1.4 km for the 1999-06-21 Koffeifontein event located in the CK

zone.

7.5±2.2 km for the 1999-07-03 Koffiefontein event located in the CK

zone.

The results obtained showed that the depth range found is between

5.6±0.3 to 18.6±3.0 km.

The quality of the information is good because the quality of the data

was checked prior to application of the depth phase method.

Miao, Q., &

Langston, C.A.

Bulletin of the

Seismological

Society of America

97(6), 2137-2151.

Empirical distance attenuation and

the local-magnitude scale for the

Central United States.

2007 Present an example of regional attenuation for the Central United

States.

Used for the comparison of the

regional attenuation developed

by Saunders et al. (2012) for the

recalibration of the ML scale.

AM & FS

Miao, Q., &

Langston, C.A.

Seismological

Research Letters

79(2), 446-456.

Comparative study of distance

attenuation in the Central United

States and Western India.

2008 Presents two examples of regional attenuation from SCR environments

in CUS and Western India. The CUS model is that presented in Miao &

Langston (2007).

Yes Used for the comparison of the

regional attenuation developed

by Saunders et al. (2012) for the

recalibration of the ML scale.

AM & FS

Midzi, V., Hlatiwayo,

D.J., Chapola, L.S.,

Kebede, F., Atakan,

K., Lombe, D.K.,

Turyomurugyendo,

G., & Tugume, F.A.

Annali di Geofisica

Seismic hazard assessment in

Eastern and Southern Africa.

1999 Probabilistic seismic hazard study for Southern and Eastern Africa

undertaken as part of the Global Seismic Hazard Assessment Program

(GSHAP) project. The catalogue was developed to uniformly use the

MS scale.

No Used for checks but not

incorporated directly since the

parameters for the region of

interest were developed based

on South African primary

sources and the magnitudes had

been converted to MS.

AM & FS


296

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


42(6), 1067-1083.

Midzi V., Saunders,

I., Brandt, M.B.C., &

Molea, T.

Seismological

Research Letters

81(3), 460-466.

1-D velocity model for use by the

SANSN in earthquake location.

Keywords: velocity structure,

SANSN

2011 Velocity model for South Africa derived from travel time of phase

arrivals for recent events recorded by the SANSN on digital

instruments. The paper also reviews velocity models previously used in

the region.

Yes Used for location of earthquake

events, and checks of individual

phase readings when reviewing

conflicting instrumental

solutions.

AM & FS

Midzi, V., Zulu, S.B.,

Flint, N., Prasad, K.,

Strasser, F.O.,

Albini, P., &

Bommer, J.J.

Report 2012-0019,

Rev.0, Council for

Geoscience,

Pretoria, South

Africa, 493 pp.

Database of intensity data for South

Africa.

Keywords: Intensity, IDPs

2012 Database of macroseismic intensity observations from events with

instrumental determinations of source parameters compiled for the

Thyspunt project.

The instrumental determinations represent independent estimates of

the source parameters. These data can therefore be used for checking

the consistency of the calibration of the macroseismic analysis

methods with the local data. The data have, however, been found

insufficient to fully constrain a local relationship as in other studies

employing the Bakun & Wentworth (1997) method (see Scotti (2012)

presentation.

Yes Used in the development and

checking of the calibration

functions for the macroseismic

analysis methods implemented

in the MEEP2 software, that

were used for the determination

of source parameters for

historical earthquakes.

AM & FS

Morton, P.

Cape Monthly

Magazine 2, 253-

256.

Notes on the earthquake. 1857 Description of the effects of the 1857-08-14 earthquake in the Western

Cape. Considered in the review of the source parameters for this

event, and for completeness considerations as the report originates

from the Cape of Good Hope Observatory.



al. (2005) catalogues.

AM & FS

Musson, R.M.W.

Technical Report

WL/94/28, British

Geological Survey,

59pp.

The BGS Sub-Saharan African

earthquake catalogue.

1994 Regional catalogue of earthquakes compiled from various local and

global data sources. The South African portion of the catalogue is

based on the same primary sources

No Not used directly, incorporated

into the GSHAP catalogue of

Midzi et al. (1999)

AM & FS

Musson, R.M.W.

Annali di Geofisica

29(5), 1041-1047.

Determination of parameters of

historical British earthquakes.

1996 Includes a description of the depth determination technique

implemented in MACDEP. Illustrates determination of source

parameters from macroseismic intensity data using examples from the

UK.

Used to guide calibration and

interpretation of intensity

analysis methods

FS & AM


297

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Musson, R.M.W.

Open Report

OR/09/045, British

Geological Survey,

16pp.

MEEP 2.0 User Guide. Earth

Hazards and Systems Programme

2009 User manual of the MEEP2 software used to determine source

parameters from macroseismic intensity data.

Yes Used to guide the application of

the different methods


software

AM & FS

Musson, R.M.W., &

Jiménez, M.J.

NERIES Technical

Report NA4-D3,

41pp.

Macroseismic estimation of

earthquake parameters.

2008 Report presenting a comparison of various techniques to determine

source parameters from macroseismic intensity data, including MEEP,

Bakun & Wentworth and Boxer Illustrates their application with

examples from Europe, in particular Italy.

Yes The techniques reviewed

(except for the Greek technique

under development) were used

as implemented in the MEEP2

software.

FS & AM

Nguuri, T.K., Gore,

J.,James, D.E.,

Webb, S.J., Wright,

C., Zengeni, T.G.,

Gwavava, O.,

Snoke, J.A., &

Kaapvaal Seismic

Group

Geophysical

Research Letters

28(13), 2501-2504.

Crustal structure beneath southern

Africa and its implications for the

formation and evolution of the

Kaapvaal and Zimbabwe cratons

Keywords: crustal structure, Moho

depth

2001 Derived crustal thickness of Southern Africa using receiver functions.

The paper also includes a description of the temporary array deployed

as part of the South African Seismic Experiment (SASE), which

provided waveform data for the assessments of additional depth values

and focal mechanisms.

Yes Used in review of crustal

thickness, and to provide an

overview of the SASE.temporary

array.

AM & FS

Nowack, R.L., &

Boore, D.M.

Unpublished

manuscript, cited in

Somerville et al.

(1987).

Body wave modeling of the Ceres,

South Africa earthquake of

September 29, 1969

Keywords: moment tensor, focal

mechanism, focal depth

1986 Using waveform modeling, moment tensor and focal depth were

determined for the 29 September 1969 Ceres event.. The solution

yields a strike-slip fault.

The mechanism is broadly consistent with other solutions for this

event.

No Unpublished solution, paper

retracted by the authors

following review comment

highlighting technical problem in

their analysis (D. Boore,

personal communication)

AM & FS

Nuttli, O.W. Seismic wave attenuation and 1973


298

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Journal of

Geophysical

Research 78(5),

876-885.

magnitude relations for eastern

North America.

Oliver, H.O.

Transactions of the

Geological Society

of South Africa 59,

123-129.

South African earthquakes –

January 1953 to December 1955

Keywords: South African

earthquakes, catalogue,

completeness

1956 Presents the catalogue of events recorded by the Geological Survey

network 1953-1955, including locations, magnitudes and felt reports.

Also includes a listing of events recorded in the wider region.

Yes Main primary source of

catalogue data for the years

concerned (supplemented by

the relevant seismological

bulletins)

Same usage for completeness

analysis as the Gane & Oliver

(1953) data.

FS & AM

Oliver, H.O.

Unpublished

earthquake

catalogue, included

in Fernández &

Guzmán (1979).

Unpublished earthquake catalogue 1970 Additional source parameters compiled from analysis of the Geological

Survey network 1956-1968, using the same techniques as Oliver

(1956)



al. (2005) catalogues. Cross-

checked against the

corresponding seismological

bulletins.

FS & AM

Reasenberg, P.

Journal of

Geophysical

Research 90, 5479-

5495.

Second-order moment of central

Californian seismicity, 1969-1982.

Keywords: seismicity, second-order

moment, California

1985 Cluster-link based technique developed to investigate physical

processes linking mainshocks and dependent events in central

California.

Focus of the study is more on physical processes, than on seismic

hazard applications. Nevertheless, Reasenberg (1985) finds that the

declustered catalogue is Poissonian in space and time. The technique

subsequently became widely used for seismic hazard applications,

probably due to the widespread availability of the code.

This result is contradicted by more recent analyses using an extended

catalogue for the same region (which in theory should have similar

calibration parameters), as shown in Figure 1 of Van Stiphout et al.

(2012).. The cumulative number of events curve of the declustered

catalogue clearly still features short-term noise (vertical steps), and

overall the technique seems to keep more events in the declustered

No The overall assessment of this

technique is that this technique,

while founded on sound physical

bases, suffers from a strong

sensitivity to its calibration

parameters, which may lead to

declustered catalogues that are

non-Poissonian in nature

through retention of events that

are flagged as dependent by

other techniques. This pattern of

behaviour is expected to

detrimentally affect the

estimation of recurrence rates

FS & AM


299

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


catalogue than other approaches leading to smoothly increasing

cumulative number of events curves. Similar results can also be found

in Luen & Stark (2012), again for a Californian catalogue.

The analysis by Tibi et al. (2011) also points to a high sensitivity of this

method to its multiple calibration parameters, in particular those

characterising the catalogue (magnitude threshold, uncertainty

estimate). The Ebel (2009) study points to the fact that the calibration

of the Omori-law parameters is less likely to be an issue.

(bias towards small events). The

difficulty of reproducing

Reasenberg’s conclusions even

when using Californian data also

leaves little hope of a stable

calibration with the sparse

catalogue considered here,

which is further more affected by

significant uncertainties. The

Reasenberg technique is

therefore not applied here.

Reasenberg, P.A., &

Oppenheimer, D.

USGS Open-File

Report 85-739,

United States

Geological Survey.

224

FPFIT, FPPLOT, and FPPAGE :

Fortran computer programs for

calculating and displaying

earthquake fault plane solutions.

Keywords: polarities, focal

mechanism

1985 Computer programs used to obtain focal mechanism based on

polarities.

Yes Used for some events having at

least 4 readings

AM & FS

Richter, C.F.

Bulletin of the

Seismological

Society of America

25, 1-32.

An instrumental earthquake scale. 1935 Original definition of the Richter local magnitude. This definition was

used for early magnitude determinations

Yes Used to obtain recalibrated ML

values consistent with the local

attenuation function determined

by Saunders et al. (2012).

AM & FS

Richter, C.F. (1958).

W.H. Freeman, San

Francisco, 768 pp.

Elementary Seismology. 1958 Classic seismology textbook. Contains the travel-time tables used for

ML determinations up to the introduction of SEISAN and the Hutton &

Boore (1987) formulation.

Yes Used to obtain recalibrated ML

values consistent with the local

attenuation function determined

by Saunders et al. (2012).

AM & FS

Rietbrock, A., &

Drouet, S.

CGS Report 2012-

0008, Council for

Determination of stochastic

simulation parameters for South

Africa based on weak-motion

recordings from the South African

National Seismic Network

2012 Study performing inversions of South African weak-motion data using

two different techniques, specifically for the Thyspunt project. The input

data set is a selection of the digital data recorded in the time span

2006-2011 selected using quality criteria.

In particular, this provides M0 estimates that are used to constrain the

Yes M0 values from both techniques

very close.

Magnitude range covered by the

dataset generally below the

magnitude range of interest for

AM & FS


300

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Geoscience,

Pretoria.

low-magnitude part of the ML-Mw relation. the catalogue development.

Saunders, I., Brandt,

M., Steyn, J., Roblin,

D., & Kijko, A.

Seismological

Research Letters

79(2), 203-210.

The South African National

Seismograph Network

Keywords: catalogue, probability of

detection

2008 Presents an overview of the South African Seismic Network, which is

used to inform the assessment of probabilities of detection for the

relevant period.

Yes The instrumental catalogue for

the project is mainly composed

of events located by this network

AM & FS

Saunders, I. CGS unpublished investigation 2012 In an effort to add more focal plane solutions, 7 events were

investigated: the 2007-03-11 Leeu-Gamka event in the KAR zone

(Event 1), the 2010-11-21 Augrabies event in the NAM zone (Event 2),

the 2010-12-25 Augrabies in the NAM zone (Event 3), the 2010-12-25

at 23h28’ in Augrabies event in the NAM zone (Event 4), the 2010-12-

28 Augrabies event in the NAM (Event 5), the 2011-01-04 Augrabies

event in the NAM zone (Event 6) and the 2011-12-18 Augrabies event

in the NAM (Event 7).

Event 1:

The location of this event is 32.834°S and 22.081°E. First-motion P-

wave polarities as recorded by the South Africa National Seismological

Network (SANSN) were used to derive the focal mechanism. Two

computer programs FOCMEC and FPFIT were also used to determine

the solution (Figure 6.8.26). Using FOCMEC, the solution obtained is

strike=103°, dip=68° and rake=151°, while FPFIT gave the following

solution: strike=212°, dip=61° and rake=28°. Both solutions obtained

yield a strike-slip fault-type.

Event 2:

The 21st November 2010 Augrabies earthquake occurred at 28.684°S

and 20.393°E. Using first-motion P-wave polarities as recorded by the

SANSN, the focal mechanism solution was obtained. Two computer

programs FOCMEC and FPFIT were used to derive the solution

(Figure 6.8.27). Using FOCMEC, the solution obtained is strike=21°,

dip=52° and rake=18°, while FPFIT gave the following solution:

strike=37°, dip=61° and rake=28°. Both solutions obtained yield a

Yes The styles of faulting for these

events were used for the future


NAM and the KAR seismic

zones.

AM & FS


301

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


strike-slip fault-type.

Event 3:

This event occurred at 28.795°S and 20.507°E. Using first-motion P-

wave polarities as recorded by the SANSN stations, the focal

mechanism solution was obtained. Two computer programs FOCMEC

and FPFIT were used to derive the solution (Figure 6.8.28). Using

FOCMEC, the solution obtained is strike=16°, dip=53° and rake=17°,

while FPFIT gave the following solution: strike=26°, dip=56° and

rake=23°. Both solutions obtained yield a strike-slip fault-type.

Event 4:

The location of this event is 28.718°S and 20.414°E. Using first-motion

P-wave polarities as recorded by the SANSN stations, the focal






Event 5:

This event was located at 28.833°S and 20.519°E. For the routine

location, first-motion P-wave polarities as recorded by the SANSN

stations helped to derive the focal mechanism solution (Figure 6.8.30)

using two computer programs: FOCMEC and FPFIT. With FOCMEC,

the solution obtained is strike=10°, dip=52° and rake=16°, while FPFIT

gave the following solution: strike=26°, dip=56° and rake=23°. Both

solutions obtained yield a strike-slip fault-type.

Event 6:

This event was located at 28.781°S and 20.491°E. Using first-motion

P-wave polarities as recorded by the SANSN stations, the focal






Event 7:

The 18th December 2011 Augrabies earthquake was located at


302

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


28.687°S and 20.423°E.

Using first-motion P phase polarities as recorded by the SANSN

stations, the focal mechanism solution was obtained. Two computer

programs, FOCMEC and FPFIT were used to derive the solution

(Figure 6.8.32). Using FOCMEC, the solution obtained is strike=9°,

dip=35° and rake=18°, while FPFIT gave the following solution:

strike=2°, dip=46° and rake=10°. Both solutions obtained yield a strike-

slip fault-type.

The quality of the information on focal mechanism is not very good

because only polarity data were used. But the relevance is good since

the fault parameters are among the few we have in the NAM and KAR

zone


M., Steyn, J., Roblin,

D., & Kijko, A.

Seismological

Research Letters

79(2), 203-210.

The South African National

Seismograph Network


detection

2008 Presents an overview of the South African Seismic Network (SANSN),

which is used to inform the assessment of probabilities of detection for

the relevant period.

Yes The instrumental catalogue for

the project is mainly composed

of events located by this network

AM & FS


M., Molea, T.,

Akromah, L., &

Sutherland, B.

South African

Journal of Geology

113(4), 369-380.

Seismicity of southern Africa during

2006 with special reference to the

Mw 7 Machaze earthquake.

Keywords: Machaze earthquake,

catalogue

2010 Reappraisal of 2006 seismicity following routine analysis. Focuses

strongly on the 2006 Mw 7.0 Machaze event in Mozambique and its

aftershock sequence. The reappraisal of the waveforms yields a

number of additional events at small magnitudes (below the ML 3.0

threshold used for the catalogue)..

Yes Event located in source zones

close to Thyspunt are included.

AM & FS

Saunders, I.,

Ottemöller, L.,

Brandt, M.B.C, &

Fourie, C.J.S.

Journal of

Seismology, in

Calibration of an ML scale for South

Africa using tectonic earthquake

data recorded by the South African

National Seismograph Network:

2006 to 2009.

2012 First local calibration for the local magnitude scale, using a selection of

recent (2006-2009) digital high-quality recordings from tectonic events

recorded at a minimum of 5 stations.

Also reviews previous local magnitude determination practices, which

used calibrations developed for California.

Yes All previously determined ML

values were recalibrated using

this calibration, which provides

similar attenuation to early travel

time tables used in Bulawayo.

FS & AM


303

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


press.

Scherbaum, F.

Presentation at

TNSP GMC Working

Meeting 4, London,

October 2012.

Does the Mw-ML scaling provide

constraints on the average stress

drop?

2012 Presentation investigating theoretical aspects of Mw-ML scaling, in

particular the break in scaling between small and large magnitudes.

Relates this to the kappa filter, and finds a theoretical slope of 0.67 for

the small-magnitude case.

Yes Used to support the form of the

ML-Mw relation.

FS & AM

Schorlemmer, D., &

Woessner, J.

Bulletin of the

Seismological

Society of America

98(5), 2103-2117.

Probability of detecting an

earthquake.

Keywords: detection, magnitude,

location

2008 Present a statistical method to assess probability of detection at a

network of stations, based on single-station calibrations using data

from previous events. These single-station detection thresholds are

then combined to map magnitude of detection across the region.

One advantage of this approach is that it works equally well with

sparse networks. However, the approach requires a large amount of

calibration data (currently not readily available). Application in South

Africa is further hampered by the frequent updating and reshuffling of

the network, i.e. few stations have been in the same location with the

same instrumentation, which combined with the low level of seismicity

limits the availability of sufficient data for a robust calibration of the

approach.

No The approach was assessed as

being too sophisticated for

meaningful implementation with

the data currently available.

Even if it were attainable, the

final result of the approach (a

map of magnitude of detection)

being of far higher spatial

resolution than any other

completeness assessment

possible, would eventually be

averaged spatially for the final

assessment of probability of

detection. In the light of these

considerations, the spirit of the

approach has been retained to

inform the determination of the

probability of detection values,

albeit in a more quantitative

manner due to the limitations of

the data.

FS & AM

Schweitzer, J., &

Lee, W.H.K.

Chapter 88 in:

International

Old seismic bulletins to 1920: A

collective heritage from early

seismologists

2003 Global overview of early (pre-1920) seismological stations and

surviving seismological bulletins. Lists locations and instrumentation of

the stations. Used to inform probability of detection assessments for

completeness determination.

Johannesburg station not

included. Used to assess

relative station density in the

South African region compared

to the global distribution of

FS & AM


304

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Handbook of

Earthquake and

Engineering

Seismology (Lee,

W.H.K., H.

Kanamori, P.C.

Jennings & C.

Kisslinger, Eds.),

IASPEI/Academic

Press, Burlington,

Massachusetts,

USA.

stations.

Scotti, O.

Presentation at

TNSP WS2,

Stellenbosch, 15-21

January 2012.

Inferring geometrical spreading

from the attenuation of

macroseismic intensity with

distance.

2012 Presentation at WS2, dealing with the issue of selecting an IPE

appropriate for the region, the local data being insufficient to allow a

bespoke calibration. In particular, presents the Bakun & Scotti (2006)

French SCR model in the context of global SCRs, showing a good

agreement with data from India and Australia. The geometrical

spreading coefficient (beta = 1.27) is found consistent with

independent determinations from neighbouring regions. Also includes

tests using South African data from events with instrumental

determinations of source parameters.

Used to support the choice of

the Bakun & Scotti (2006)

French SCR model as the IPE

used for the determination of

source parameters from

intensity data.

FS & AM

Shearer, P.M. &

Stark, P.B.

Proceedings of US

National Academy of

Sciences 109, 717–

721.

Global risk of big earthquakes has

not recently increased.

Keywords: earthquake, global risk,

catalogue, declustering

2012 Study of large-magnitude (Mw ≥7.0) global seismicity using ISC and

NEIC data with Mw determinations.

Dataset biased towards active and subduction events due to its global

nature.

Moderate quality reflects the fact that objective of study is not the

testing of declustering techniques and that the data is mostly from

different tectonic regimes than that of interest.

Find that catalogue declustered using a simple windowing technique is

consistent with a Poisson hypothesis, whereas original non-

declustered catalogue was not.

Yes Used to support the well-

behaved nature of the Gardner

& Knopoff (1975) algorithm in

terms of yielding a Poissonian

catalogue, even when using a

global dataset, rather than a

Californian one.

FS & AM

Shudofsky, G.N

Geophysical Journal

Source mechanism and focal

depths of East African earthquakes

using Rayleigh-wave inversion and

1985 In this study, Rayleigh-wave waveform inversion and body-wave

waveform modelling for some African earthquakes are presented. The

list includes three earthquakes in South Africa:

Yes The focal depth and fault

parameters obtained were of

good quality since a waveform

AM & FS


305

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


of the Royal

Astronomical Society

83, 563-614.

body-wave modelling

Keywords: source mechanism,

focal depth, Rayleigh-wave

inversion, modelling

The 1969-09-29 Ceres and its 1970-04-14 aftershock, and

the 1971-07-01 Koffiefontein earthquakes.

The inversion yields a strike-slip focal-mechanism (strike=310°,

dip=82° and slip=180°) and focal depth = 30km for Ceres, a strike-slip

mechanism (strike=334, dip=74 and slip=160) and focal depth = 10km

for the Ceres aftershock, and normal-oblique faulting (strike=300,

dip=63 and slip=219) and depth = 6km for Koffiefontein.

inversion method was used. The

results were used to inform the

development of a depth

distribution, as well as the style-

of-faulting of the CK and SYN

zones.

Sieberg, A.

. In: Gutenberg, B.

(ed.), Handbuch der

Geophysik, Vol. 4,

Bornträger, Berlin,

Germany.

Erdbebengeographie

1932 Global compilation of earthquake listings and associated macroseismic

information by region. Contains several tables listing South African

earthquakes, as well as a composite map of felt areas. This information

was considered in both the catalogue work and the development of the

macroseismic database, but not used due to quality problems.

No Found to contain gross location

errors and fake events. This

reference is generally

considered problematic by

historical seismologists due to

the fact that primary sources are

not referenced. Superseded by

the Albini (2012) study for the

historical part, and redundant

with South African observatory

records for the instrumental part.

AM & FS

Singh, M., &

Hattingh, E.

Natural Hazards

50(2), 403-408.

Short communication: Collection of

isoseismal maps for South Africa.

2009 Collection of isoseismal maps for South African events, compiled from

published and unpublished

No Superseded by Midzi et al.

(2012)

AM & FS

Smith, M.R.G.

Report 1999-0139,

Council for

Geoscience,

Pretoria, 19 pp. 225

A catalogue of relocated seismic

events around the Koeberg site.

1999 Provides some reanalyses of a number of events in the Western and

Northern Cape, performed using the original waveforms and the

SEISAN software. Difference with original analysis is that S-wave

arrival times are considered in addition to P-wave arrival times, which

in some cases improves the location.

Yes Included in the review of

possible solutions for the events

concerned.

AM & FS

Snoke, J. A.,

Munsey, J.W.,

Teague, A.G., &

A program for focal mechanism

determination by combined use of

polarity and SV-P amplitude ratio

1984 FOCMEC computer programs used to obtain focal mechanism based

on polarities and amplitude of S-waves.

Yes Used for some events (when

data were sufficient for a

determination) to determine

AM & FS


306

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Bollinger, G.A.

Earthquake Notes

55, 15.

data. focal mechanism

Somerville, P.,

McLaren, J.P.,

LeFevre, L.V.,

Burger, R.W., &

Helmberger, D.V.

Bulletin of the

Seismological

Society of America

77(2), 322-346.

Comparison of source scaling

relations of eastern and western

North American earthquakes.

1987 Study of source properties of ENA earthquakes, compared to those of

the Western US. The paper also includes some discussion of other

SCR.

Lists the Nowack & Boore focal mechanism solution for the 1969 Ceres

earthquake.

Included in EPRI94 (Johnston et al., 1994) SCR study.

No Nowack & Boore solution was

never published following

decision of the authors to retract

the paper after one reviewer

pointed out a problem with the

inversion process (personal

communication from D. Boore).

AM & FS

Storchak D.A.

Personal communication

2009 Reanalysis of the ISC solution for the 1969 Ceres and 1976

Koffiefontein events, including sensitivity tests.

For the Ceres event, a solution with free depth could not be obtained,

however a fixed depth of ~10km agreed well with the obsevations.

For the Koffiefontein event, a focal depth between 7 to 11km was

determined. This is shallower than the original ISC estimate.

Yes Included in the compilation of

focal depth values used in the


distribution.

AM & FS

Stucchi, M., Albini,

P., Mirto, C., &

Rebez, A.

Annali di Geofisica

47(2-3), 659-673.

Assessing the completeness of

Italian historical earthquake data.

Keywords: completeness, historical

earthquake, Italian.

2009 Presents an overview of the historical approach to assessing

completeness, which considers the availability and likelihood of

survival of earthquake reports, in the light of both positive and negative

evidence. The approach is illustrated with the example of the Italian

catalogue.

Yes This approach was implemented

in the Thyspunt study via the

historical assessment of

completeness in Albini (2012),

which was later incorporated in

the determination of the

probabilities of detection.

FS & AM

Szeliga, W., Hough,

S., Martin, S., &

Bilham, R.

Bulletin of the

Seismological

Intensity, magnitude, location, and

attenuation in India for felt

earthquakes since 1762.

2010 Study applying the Bakun & Wentworth (1997) method to macro

seismic data from India. The resulting IPE is extremely similar to the

Bakun & Scotti (2006) French SCR IPE. Also discuss some practical

aspects of the implementation of the Bakun & Wentworth method.

Yes Used in the review of published

IPEs, in particular to support the

portability of the Bakun & Scotti

(2006) French SCR IPE to other

regions

FS & AM


307

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Society of America

100(2), 570-584.

Theron, J.N. (1974).

In: Van Wyk, W.L. &

L.E. Kent (Eds.). The

earhquake of 29

September 1969 in

the south-western

Cape Province,

South Africa.


4, Geological Survey

of South Africa.

The seismic history of the south-

western Cape province.

1974 First listing of events compiled specifically for the Western Cape

region, including 50 events that occurred between 1620 and 1971, for

which a description of the felt effects could be found.

Descriptions of felt effects accompanied by maximum intensity values

deduced from available information. Magnitude values also listed,

mostly derived from intensity values.

Locations are provided only in the form of geographical place names;

no epicentral coordinates are provided.



al. (2005) catalogues. Detailed

information listed in Theron

(1974) was used in the review of

source parameters for the

events listed, also to retrieve the

original intensity values

assigned by Theron to assess

magnitudes from these, rather

than converted ML values.

FS & AM

Tibi, R., Blanco, J., &

Fatehi, A. Tibi, R.,

Blanco, J., & Fatehi,

A.

Seismological

Research Letters

82(4), 509-518.

An alternative and efficient cluster-

link approach for declustering of

catalogues

Keywords: catalogue, declustering

2011 Develop an extension to the Reasenberg (1985) cluster-link technique

in which the time links are based on a simple magnitude-dependent

function, instead of the Poissonian assumption.

Discuss the limitations of the Reasenberg (1985) approach, in

particularity its sensitivity to calibration parameters such as the upper

bound on the interaction time window.

While their discussion of the calibration issues associated with the

Reasenberg (1985) algorithm is useful, most of the limitations in terms

of applying the method to a sparse catalogue remain. In particular, the

method remains sensitive to catalogue-specific parameters such as the

minimum cut-off magnitude, as well as location errors in terms of

epicentral location and depth (which are significant in the case of the

Thyspunt catalogue)

The example applications shown (Slovenia and Middle East) are

interesting because they correspond to much sparser catalogues than

other applications based on Californian data. The authors include a

residual analysis which supports their claim that their proposed

approach leads to a closer fit with the Poissonian assumptions.

However, this appears to be contradicted by the results shown in

Figure 5 and 7, where the closest (visual) match to the Poissonian

Yes While the technique is not

assessed to be a viable

declustering option for the

Thyspunt catalogue, the

discussion and results

presented in this paper inform

the selection of the Gardner &

Knopoff (1974) algorithm as sole

declustering alternative.

FS & AM


308

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


curve appears to be for the original (non-declustered) catalogue.

Udías, A., &

Stauder, W.

Seismological

Research Letters

67(3), 10-19.

The Jesuit Contribution to

Seismology.

1996 Overview of the history of seismograph stations installed in Jesuit

observatories, including the station at Antananarivo (TAN) in

Madagascar.

Yes Used to obtain the date of

establishment of the TAN station

FS & AM

Uhrhammer, R.A.

Earthquake Notes

57, 21.

Characteristics of northern and

central California seismicity

1986 Alternative magnitude-dependent windows for a window-based

approached using Central and Northern Californian data.

Windows are very different from Gardner & Knopoff (1974) windows,

despite the good agreement of the latter with the windows

independently determined for another region by Grünthal (1985).

Tested as a declustering option but rejected as the results showed

poor performance.

No Visual examination of results

individual clusters and overall

performance with Thyspunt

catalogue shows unsatisfactory

performance (many obvious

dependent events such as

immediate aftershocks not

removed).

Therefore, this approach is not

considered further as the

calibration is assessed to be

inappropriate for South Africa.

FS & AM

USNRC

NUREG-2115, US

Nuclear Regulatory

Commission,

Washington D.C.

Central and Eastern United States

Seismic Source Characterization for

Nuclear Facilities


detection

2012 Includes application of Veneziano & Van Dyck (1985) and Gardner &

Knopoff (1974) technique to CEUS SSC catalogue

Presents the application of the probability of detection approach to

completeness to the CEUS SSC catalogue.

Resulting numbers of independent events given by both approaches

are very similar, which supports the finding that the Gardner & Knopoff

(1974) windows can be applied outside of Southern California and

provide a good estimate of long-term Poissonian rate.

The full approach involves a data-driven assessment of the probability

of detection approach using a maximum-likelihood approach. This was

replaced here by a more qualitative assessment of the average

probability of detection for each source zone.

Also provides methodology for magnitude uniformisation, Mmax

calculation and recurrence calculations.

Yes Report as a whole used as a

methodological guide for

catalogue analysis and

recurrence calculations.

methods were implemented

where possible, but

implementation of the more

sophisticated methods was often

hampered by the paucity of data

available.

FS & AM

USGS NEIC USGS PDE catalogue 2011 The information on the 18th December 2011 Augrabies earthquake, for

which USGS used waveform inversion used to determine a moment

Yes The styles of faulting for these

events were used to

AM & FS


309

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


tensor solution. Seismic moment, moment magnitude and focal

mechanism were then obtained. To estimate the centroid focal depth,

synthetic seismograms were compared to the observed seismograms.

The result showed that the mechanism was of strike-slip type faulting

(strike1=254°, dip1=78° and rake1=-21°, and strile2=349°, dip2=70°

and rake2=167°). The seismic moment, moment magnitude and focal

depth obtained were 4.10E+16dyne-cm, 4.3 and 10km, respectively.

The information was of very good quality and relevance since ISC used

moment tensor inversion and the solution was consistent with the

mechanism in the Augrabies area.

characterize future earthquake

in the NAM zone, and provides

the Mw value of 4.3 for the

2011-12-18 Augrabies event.

Van Stiphout, T.,

Schorlemmer, D., &

Wiemer, S.

doi:10:5078/corssa-

52382934. Available

at

http://www.corssa.or

g.

Seismicity declustering. Community

Online Ressource for Statistical

Seismicity Analysis

Keywords: Catalogue, declustering

2012 Critical review of declustering techniques, including an application

example to a large, high-quality catalogue.

The comparison presented in their figure 1 showing that the

Reasenberg technique does not produce a Poissonian declustered

catalogue (wheras the Gardner & Knopoff algorithm and other

approaches do) strongly weighed against the use of this technique.

The results also support the good agreement between Gardner &

Knopoff (1974) declustering and rate-thinning techniques (in this case,

Zheng et al., 2002).

Yes Used to compare the various

options available for

declustering. The example

shown is for California, where

data is plentiful. The relative

performance of the techniques

in this case was combined with

considerations regarding the

feasibility of achieving a stable

calibration with sparse data.

FS & AM

Veneziano, D. & Van

Dyck, J.

in Seismic Hazard

Methodology for

Nuclear Facilities in

the Eastern U.S.,

Volume 2, Appendix

A-4, EPRI/SOG

Draft 85-1.

Statistical discrimination of

aftershocks and their contribution to

seismic hazard

1985 Declustering technique based on rate-thinning applied to CEUS

catalogue in EPRI94 study and later applied in USNRC (2012) CEUS

SSC study.

Specifically developed for seismic hazard application, in particular the

calculation of long-term Poissonian rates

Shown in CEUS SSC (2012) to give very similar results to the Gardner

& Knopoff (1974).

No Not used here as the very

sparse nature of the catalogue

might lead to calibration issues

and/or numerical stability issues,

whereas results from the more

plentiful (but still sparse) CEUS

SSC catalogue show that the

results are similar to applying

the windowing approach.

FS & AM

Wahlström, R. Magnitude-scaling of earthquakes 1979 Describes the development of a magnitude scale for Fennoscandia, Yes Precedent for correcting local FS & AM


310

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Geophysica 16(1),

51-70. 226

in Fennoscandia. including corrections to the local magnitude values determined using

the original Richter (1935) calibration.

magnitudes calculated using the

Richter (1935) calibration

Wagner, G.S. &

Langston, C.A.

Geophysical Journal

94(3), 503-518.

East African earthquake body wave

inversion with implications for

continental structure and

deformation

Keywords:East African earthquake,

body-wave inversion, continental

structure, deformation

1988 5 African earthquakes including the 1969-09-29 Ceres were

investigated.

Waveform inversion and waveform fitting method were used to

determine the mechanism and focal depth of this event. Long-period

WWSSN seismograms (recorded on 75cm film chips) were digitized.

Both P-wave and SH-wave were used to obtain the focal solution

(Figure 6.8.5). The two solutions derived using P-waves and SH-waves

showed a nearly pure strike-slip fault: (1) strike of 124° and dip of 88°

and (2) a strike of 217° and a dip of 89°. The focal depth determined

was 4km.

The information were of very good quality and relevance because of

the method used and the location of the event (SYN zone)

Yes The team used the results for

the earthquake characteristics in

the SYN zone, and the


distribution.

AM & FS

Wamboldt, L.R.

MSc thesis, Queen’s

University, Ontario,

Canada, 199 pp.

An Automated Approach for the

Determination of the Seismic

Moment Tensor in Mining

Environments.

Keywords: moment tensor,

inversion methods

2011 Compilation of methods used in moment tensor in earthquake

seismology in general, with application to mining seismology.

Yes. Used to inform the prioritisation

of focal mechanism solutions in

case of many solutions.

AM & FS

Weichert, D.H.

(1980).

Bulletin of the

Seismological

Society of America

70(4), 1337-1346.

Estimation of the earthquake

recurrence parameters for unequal

observation periods for different

magnitudes.

1980 Original formulation of the maximum-likelihood method used for the

recurrence calculations. The method relies on maximising the

likelihood of observing given counts of earthquakes in magnitude bins

over bin-dependent periods of completeness.

Yes Adapted to use equivalent

periods of completeness

following CEUS practice.

Calculation remains the same.

FS & AM

Wiemer, S.

Seismological

Research Letters,

72, 373-382.

A software package to analyze

seismicity: ZMAP


completeness, declustering,

2001 Software used for Gardner & Knopoff (1974), Grünthal (1986) and

Uhrhammer (1986) declustering algorithms

Reasenberg (1985) algorithm also included in the software but not

used due to difficulty in determining a reliable calibration

Yes Software used for declustering,

completeness assessment using

maximum curvature method and

determination of regional b-

value used as prior in

FS & AM


311

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


recurrence calculations Software used for completeness assessment instrumental subset of

the data available digitally, (i.e since 1997) using maximum curvature

method, as well as determination of regional b-value used as prior in


This analysis indicated Mc ~2.0 from 1997, Mc ~ 1.9 from 2003, and

Mc 1.8 from 2007. These results are consistent with those found by

Brandt (2011) for the whole network.


Wiemer, S., & Wyss,

M.

Bulletin of the

Seismological

Society of America

90(3), 859-869.

Minimum magnitude of complete

reporting in earthquake catalogs:

examples from Alaska, the Western

United States, and Japan

Keywords: magnitude, catalogue,

completeness

2000 Presents the maximum curvature approach used to determine the

magnitude of completeness for the more recent instrumental data

(1997-2011)

Yes The results were used to inform


values assigned for the relevant

period.

FS & AM

Willemann, R.J.

Seismological

Research Letters

70(3), 313-321.

Regional Thresholds of the ISC

Bulletin


completeness, magnitude

1999 Provides a study of regional variations of the completeness threshold

of the ISC bulletin.

Gives a value of mb = 4.3 for the African region; this is used, along

with other information, to set the completeness threshold at Mw 4.5

from the establishment of the WWSSN in 1964

Yes Informs completeness in terms

of probability of detection by

modern instrumental global

networks.

FS & AM

Woessner, J., &

Wiemer, S.

Bulletin of the

Seismological

Society of America

95(2), 684-698.

Assessing the quality of earthquake

catalogues: estimating the

magnitude of completeness and its

uncertainty

Keywords: catalogue, magnitude,

completeness

2005 Discusses pros and cons of the various approaches for statistical

determination of the magnitude of completeness linked to the

maximum curvature approach.

This information was used to inform the determination of the magnitude

of completeness for the more recent instrumental data (1997-2011)

Yes The results were used to inform


values assigned for the relevant

period.

FS & AM

Wood, H.E.

Bulletin of the

Seismological

Society of America

11, 113-120.

On the occurrence of earthquakes

in South Africa.

1913 Summary of the information gathered at the Union Observatory in

Johannesburg, predominantly based on macroseismic information

gathered from newspaper clippings or reports sent by members of the

public to the observatory.

Yes Includes isoseismal maps for

three events.

Incorporated into Finsen (1950)

and subsequent catalogues/

AM & FS


312

Author6 Title

Year


Is the data

used in the

SSC

model?

(yes, no)


Wright, C,. &

Fernández, L. M.

Lee, W.H.K., H.

Kanamori & P.C.

Jennings (Eds),

International

Handbook of

Earthquake and

Engineering

Seismology.

International

Geophysics 81(B),

1433-1434.

Chapter 79.48: South Africa

Keywords: seismic monitoring,

detection, seismicity

2003 Presents an overview of the history of seismic monitoring in South

Africa, which is used to inform the assessment of probabilities of

detection for the relevant period.

Yes A few slight inconsistencies with

archive materials have been

corrected in this assessment,

hence the level of reliance is

assessed as moderate.

FS & AM

Zhuang, J., Ogata,

Y., & Vere-Jones, D.

Journal of the

American Statistical

Association. 97, 369-

380.

Stochastic declustering of space-

time earthquake occurrences

Keywords: declustering, earthquake

occurrence, catalogue

2002 Stochastic technique to identify declustering events using a thinning

operation for Poissonian point processes.

Similar in nature to the Veneziano & Van Dyck (1985) approach.

Shown by Van Stiphout et al. (2012) to give a good agreement with the

Gardner & Knopoff (1974) results for the same catalogue.

No Not used here due to insufficient

data for a meaningful calibration.

Illustrates the good agreement

between the simple windowing

method of Gardner & Knopoff

(1974) with more sophisticated

declustering methods designed

specifically for seismic hazard

applications.

FS & AM



313

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326

4. Data Evaluation Tables

Although Data Summary tables are developed for every data set considered, Data Evaluation

tables are reserved for only those data that were actually relied upon in the development of the

SSC model. Therefore, the tables are designed to document the aspects of the SSC model that

were informed by the particular data set and the judgments by the TI Team expert evaluators of

the degree of reliance placed on the data and the quality of the data. The Data Evaluation

tables include the following information:

• Naming of the table according to whether it applies to a seismic source zone,

fault, source, the entire SSC model, or a particular methodology used in the

development of the SSC model

• Author

• Title

• Year

• Relevant Information (relative to the four criteria for identifying seismic sources)

• Use for SSC: Quality and Reliance ratings for each of the following:

o Fault or Seismic Source Characteristics

� Seismogenic Probability

� Seismic Source or Fault Geometry

� Recurrence/Recency & Slip Rate/Recurrence Intervals

� Mmax

o Future Earthquake Characteristics

� Rupture Geometry (strike, dip)

� Style of Faulting

� Seismogenic Thickness

The “relevant information” field of the table is the location where the evaluator includes the

specific information in the data set that relates to the four criteria for identifying seismic sources.

For example, if a particular paper provides information that has been used to define the

boundaries of a seismic source zone, that would be indicated here. In addition to defining the

manner in which the data were used, the Data Evaluation tables also document the evaluator

expert’s perceptions of the quality of the data for the objectives of SSC (with a rating of 1 to 5)

and the degree of reliance placed on the data in assessing each of the characteristics (rating of

1 to 5). This information provides important insights to readers of the report such that they gain

an understanding of which data are perceived to have the highest quality and that were relied

upon most heavily by the TI Team.


327

Table 4.1. Data Evaluation Table 6.4. Focal Depth

Author Title Year Relevant Information7

Use for SSC (Quality8/Reliance9)

Fault or Seismic Source Characteristics Future Earthquake Characteristics

Probability of

Activity

Seismic Source or

Fault Geometry

Recurrence/Recency &

Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

Brandt, M.B.C.

& Saunders, I.

New regional moment

tensors in South Africa

2011 Style of faulting and Seismogenic

thickness

Time domain surface wave waveform

inversion technique was used to

derive moment tensor solutions,

moment magnitude and focal depth for

2 mine-related and 1 tectonic events.

The mining events studied are: the

25th September 1997 Far West Rand

and the 5th December 1998 Far West

Rand earthquakes. The tectonic event

studied is the 1999-02-04 Fauresmith,

in the Koffiefontein area.

The focal depth from waveform fitting

obtained were:

The 25th September 1997 Far west

rand event: 2km.

The 5th December 1998 Far West

Rand event: 1km.

The 04th February 1999 Fauresmith

event 11km.

The quality of this information is Q5

since the authors used the waveform

fitting. Depth is R5 since the events is

located in our source zones and was

used in the assessments.

. Q4:R5

The focal depth

solution for the

tectonic event

was used for the

assessment of

the future

earthquake

characteristics

in the CK

seismic source

zone. These

data were really

relevant since it

is among the

few focal depths

we had in the

area.

7 Sort by the criteria for identifying the seismic source: probability of activity, source/fault geometry, recurrence, Mmax, or future earthquake characteristics (rupture geometry, style of faulting, and seismogenic thickness).

8 Quality refers to the degree to which these particular data relate to and provide insights to the SSC model and can be used in its development . Quality (Q1=low; Q5=high)

Reliance is the degree to which the data provide direct support and justification for particular elements/parameters of the SSC Mode. Reliance (R1=low, U5= high)


328




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

Bowers, D.

The October 30, 1994,

seismic disturbance in South

Africa: Earthquake or large

rock burst?

1997 Seismogenic depth

Bowers (1997) used broad-band

waveform data from the Global

Seismographic Network (GSN)

stations to invert for moment tensor

and depth of the event. Inversion of

the relative amplitudes of body and

surface waves at regional and

teleseismic and polarities (for clear

first P onset) yielded a normal-type

focal mechanism with strike=190°,

dip=45° and slip=-70°, and a scalar

moment of 2.4E+16Nm. The fitting of

synthetic and observed seismograms

gave the best result for the depth of

2.3km.

The information on focal depth are of

quality Q5 since the full waveform

inversion method was used. This

information was not very relevant R2

since the event was not tectonic but

mine-related. And the event itself was

not located in a particular source zone.

Q5:R2

The information

on focal depth

was not used by

the team for the

source

characterization

Dziewonski, A.

M., Ekström,

G.,

Woodhouse,

Centroid-moment tensor

solutions for October–

December 1986

1987 Seismogenic depth.

In this paper, the Centroid moment

tensor solution of the 1986-10-05

Q5:R5

Information on

depth was used


329




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

J.H. & Zwart,

G.

event in Lesotho is given. For the

event, the estimated centroid depth is

15km, the moment is 1.29E+17dyne-

cm, Mw is 5.3, the fault solution is

pure normal fault with two nodal

planes having strike=168, dip=37 and

rake=-90, and strike=348°, dip=53°

and rake =-90°. The seismic moment,

moment magnitude and depth

obtained were 1.29E+17N-m, 5.3 and

15.0km, respectively.


since the authors used the centroid

moment tensor inversion to obtain the

style of fault and focal depth. The focal

depth is also relevant Q5 since the

event is located in the CK zone.

to identify

seismogenic

thickness for the

CK zone.

Dziewonski, A.

M., Ekström,

G.,

Woodhouse,

J.H. & Zwart,

G.


solutions for July–September

1990




mining event South Africa is listed. For

the event, the estimated centroid

depth is 28.3km, the moment is

3.58E+16dyne-cm, Mw is 5.3, the fault

solution is pure normal oblique fault

with two nodal planes having

strike=11, dip=45 and rake=-61, and

strike=153°, dip=52° and rake =-115°.

The seismic moment, moment

magnitude and depth obtained were

3.58E+16N-m, Mw=5.0 and 28.3km,

respectively.

The quality of this information on the

Q1:R1

Information on

depth not used

since the event

is not tectonic.


330




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

focal plane solutions is Q5 since the

authors used both the centroid

moment tensor inversion but the result

itself was not very relevant R1 since

the event is mining related. The depth

information for this event mining

related event seems deeper than

expected. This depth was given quality

Q1 and relevant R1

EHB Bulletin

Reanalysis of ISC data 1971 Seismogenic depth

The 1986-10-05 Matatiele earthquake

was reanalysed and the depth

obtained was 11.7±0.7km.

The 1989-09-29 event located at the

South Africa and Leshoto border was

also reanalysed. The solution gives a

focal depth of 7.7km.

Q4: R5

The team used

the information

on the focal

depths for the

future

earthquake

characteristics

in the CK zone.

Fan, G. &

Wallace, T.

Focal mechanism of a recent

event in South Africa: A

study using a sparse very

broadband network


Focal mechanism of the October 30,

1994 event (mb = 5.7) near the

northwestern border of Orange Free

State in South Africa is obtained using

waveform fitting. The depth of the

event is 12km and the style of fault is

normal with strike=345, dip=14 and

rake=-105. Although the event was a

mining event, the focal depth obtained

is not consistent with a mining related

.

Q1:R1

The team did

not use the

information on

focal depth

since the event

is not tectonic,

and the

interpretation as

such is

contradicted by


331




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

event (Bowers, 1997). The focal depth

being consistent with mining event, the

quality for the depth and the relevance

are Q1 and R1, respectively.

observations in

the underground

workings.

Foster, A.N.,

and Jackson,

J.A

Source parameters of Large

African earthquake:

implications for crustal

rheology and regional

kinematics

1998 Seismogenic thickness.

The 29-09-1969 Ceres earthquake:

Using analogue body-waveform data

from the WWSSN stations and digital

data from the Global Digital

Seismograph Network (GSN), P- and

SH-waves inversion and waveform

fitting methods were used to

determine the focal mechanism, focal

depth, moment tensor and moment

magnitude of the 29th September

1969 Ceres event. Two pure strike-slip

possible solutions were obtained: (1)

strike=305°, dip=87° and rake=3° and

(2) strike=215°, dip=87° and

rake=177°. A seismic moment of

3.9E+18Nm, moment magnitude of

Mw 6.4 and depth of 5km were

calculated.

The focal depth obtained for this event

is of quality Q5 since the waveform

inversion method was used, and the

relevance is R5 since the event is


Q5: R5

The focal depth

was used to

estimate the

seismogenic

depth range for

the SYN zone.

Green, W.E. &

Bloch S.

The Ceres, South Africa

earthquake of September 29,

1969. I. Report on some


Using the temporary local network

Q4: R5

The information


332




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

aftershocks.

after the September 29, 1969 Ceres

earthquake, aftershocks were

recorded and located. Most events

were located in the Ceres region.

The solution yields a maximum

aftershock depth of 9 km with most

aftershocks prior to 1970-04-14 event

(the main aftershock) shallower than

6.5 km.

The quality of the information on the

type of faulting is Q5 since very local

network was used for location and the

relevance is R5 since the event was


was used for

future

earthquake

characteristics

in the SYN

zone.

Jensen, B.L.






Using waveform inversion and

modeling of long period P- and SH-

waves, the focal mechanism, focal

depth, seismic moment and moment

magnitude of the 01-07-1976

Koffiefontein earthquake are

determined. The result of the inversion

showed that the mechanism was a

pure normal fault with strike=308°,

dip=22° and rake=-86°. The focal


magnitude were 5.5km, 2.66E+24

dyne-cm and 5.8 respectively.


focal depth is Q5 since the waveform

inversion and fitting were used, and

the relevance is R5 since the event

was located in the CK zone.

Q5: R5

The team also

used the focal

depth

information to

constrain the

seismogenic

depth in the CK

zone.


333




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

Krüger, F.,

Reichman, S.,

& Scherbaum,

F.

Moment tensor solution for

the 29.9.1969 Ceres

earthquake. SSHAC Level 3

Workshop 1, Cape Town.


In this investigation of the Ceres

earthquake, moment tensor inversion

was done using scanned and digitized

seismograms from a set of WWSSN

stations operational in 1969. For the

estimate of the solution, body- and

surface waves were used. The best

double solution obtained yielded a

strike-slip (SSE-WNW) fault with

strike=305°, dip=78° and rake=1.2°

(Figure 6.8.7), with a centroid

depth=15km.

The waveform fitting was used to

obtain focal depth. This event was

rated Q5:R5.

. Q5:R5

The Team also

used the

information on

the focal depth

was used to

constrain the

seismogenic

depth in the

SYN zone.

Mangongolo A.

CGS Unpublished

investigation on focal depth


This was an effort to obtain more focal

depth using the regional depth phases

method (RDPM) after Ma & Atkinson

(2006). The regional depth phases

used is the sPmP or the S-wave that

travels upward to the surface, converts

to a P-wave, then reflect at the Moho

and travels upward to the station and

the PmP phase associated. Using

known focal mechanism solutions,

focal depths are obtained through

waveform fitting method.

In the investigation, 9 events were

used which occurred in South Africa

and recorded by the Kaapvaal craton

seismic experiment. The depth for the

9 events are:

Q5: R4 Q5:R5

The team used

these

information to

determine the

range of

seismogenic

focal depths to

characterize the

seismic zone.


334




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

7.3±2.3 km for 1998-04-24 Augrabies

event located in the NAM zone

6.3±0.3 km for the 1998-06-22 Three

Sisters events located in the CAR

zone

14.8±1.5 km for the 1998-07-05

Lesotho event located in the CK zone

18.6±3.0 km for the 1998-09-06

Lesotho in the CK zone.

5.6±0.3 km for the 1998-10-05

Fraserburg event located in the KAR

zone

6.3±0.9 km for the 1999-01-07

Koffiefontein event located in the CK

zone.

8.1±1.5 km for the 1999-02-04

Koffeifontein event located in the CK

zone.

7.5±1.4 km for the 1999-06-21

Koffeifontein event located in the CK

zone.

7.5±2.2 km for the 1999-07-03

Koffiefontein event located in the CK

zone.

The results obtained showed that the

depth range found is between 5.6±0.3

to 18.6±3.0 km.

The quality Q5 was attributed to the

depth found because the depth phase

method was applied using good

quality data. And relevance R5 was

also attributed to these depth since

they are among the few depth we

have.


335




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

Saunders, I.,

Brandt, M.,

Molea, T.,

Akromah, L., &

Sutherland, B.

Seismicity of southern Africa

during 2006 with special

reference to the Mw 7

Machaze earthquake.


In this investigation, seimicity of

Southern Africa from January to

December 2006 is analyzed. For the

routine location, focal depth are fixed

to: (1) 0 km for explosion, (2) 2km for

mining related events, (3) 5km for

local and regional tectonic events and

(4) 10 km for distant events (Saunders

et al., 2010).

Quality Q1 and relevance R1 were

given to the depths obtained since

they have been fixed.

Q1:R1

The team did

not use these

focal depths to

characterize

future

earthquakes.

Shudofsky,

G.N.


depths of East African

earthquakes using Rayleigh-

wave inversion and body-

wave modeling


In this study, Rayleigh-wave waveform

inversion and body-wave waveform

modeling for some African

earthquakes are presented. The list

includes two earthquakes in South

Africa:

The 1969-09-29 Ceres and its 1970-

04-14 aftershock, and

the 1971-07-01 Koffiefontein

earthquakes.

The inversion yields a strike-slip focal-

mechanism (strike=310°, dip=82° and

slip=180°) and focal depth = 30km for

Ceres, a strike-slip mechanism

(strike=334, dip=74 and slip=160) and

focal depth = 10km for the Ceres

aftershock, and normal-oblique

faulting (strike=300, dip=63 and

slip=219) and depth = 6km for

Q5: R5

The Team used

the information

on focal depth to

determine the

seismogenic

depth in the

SYN and the CK

zones.


336




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

Koffiefontein.

Quality Q5 and R4 were also given to

the depth obtained, because of

waveform fitting was used and the

locations of the two events in our

source zones.

Storchak D.A. Personal communication 2009 Seismogenic depth.

The September 29, 1969 Ceres event

was reanalyzed. A solution with free

depth could not be obtained. A fixed

depth of ~10km.

agreed well with the results.

The July 01, 1976 Koffeifontein

earthquake was also reanalyzed. The

solution yield a focal depth between 7

to 11km.

.

Q3:R3

USGS NEIC USGS PDE catalogue 2011 Seismogenic depth

The information on the 18th December

2011 Augrabies earthquake located at

28.687°S and 20.423°E, was retrieved

from the ISC bulletin.

USGS used waveform inversion used

to determine the moment tensor

solution for this event. Seismic

moment, moment magnitude and focal

mechanism were then obtained. To

estimate the centroid focal depth,

synthetic seismograms were


seismograms. The result showed that

Q5:R5

The Team used

the information

on focal depth to

determine the

seismogenic

depth in the

NAM zone.


337




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

the mechanism was of strike-slip type

faulting (strike1=254°, dip1=78° and

rake1=-21°, and strile2=349°,

dip2=70° and rake2=167°) (Figure

6.8.33). The seismic moment, moment

magnitude and focal depth obtained

were 4.10E+16dyne-cm, 4.3 and

10km, respectively.

Quality Q5 and R5 were also given to

the depth obtained since the waveform

fitting was used and the event is

located in NAM seismic zone.

Wagner, G.S.

& Langston,

C.A.

East African earthquake

body wave inversion with

implications for continental

structure and deformation


5 African earthquakes including the

1969-09-29 Ceres were investigated.

Waveform inversion and waveform

fitting method were used to determine

the mechanism and focal depth of this

event. Long-period WWSSN

seismograms (recorded on 75cm film

chips) were digitized. Both P-wave

and SH-wave were used to obtain the

focal solution (Figure 6.8.5). The two

solutions derived using P-waves and

SH-waves showed a nearly pure

strike-slip fault: (1) strike of 124° and

dip of 88° and (2) a strike of 217° and

a dip of 89°. The focal depth

determined was 4km.

Q5 and R5 were attributed to the focal

depth solution because of the method

used and the location of the event

(SYN zone).

. Q5: R5

The team used

the focal depth

solution to

determine the

seismogenic

depth range in

the SYN zone.


338




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness



339

References



Brandt, M.B.C. & Saunders, I. (2011). New regional moment tensors in South Africa.


Dziewonski, A. M., Ekström, G., Woodhause, J.H., & Zwart, G. (1987). Centroid-moment tensor

solutions for October-December 1986. Physics of the Earth and Planetary Interiors 48, 5–17.

Dziewonski, A. M., Ekström, G., Woodhause, J.H., & Zwart, G. (1991). Centroid-moment tensor

solutions for July-September 1990. Physics of the Earth and Planetary Interiors 67, 211-220.

Fan, G. & Wallace, T. (1995). Focal Mechanism of a Recent Event in South Africa: A study

using a Sparse Very Broadband Network. Seismological Research Letters 66(5), 13-18.



422-448.

Green, R.W.E, & Bloch, S. (1971). The Ceres, South Africa, earthquake of September 29, 1969.

I. Report on some aftershocks. Bulletin of the Seismological Society of America 61(4), 851-859.


continental interior of Africa. MSc thesis, Memphis State University, 106 pp.

Krüger, F., Reichman, S., & Scherbaum, F. (2011). Moment tensor solution for the 29.9.1969

Ceres earthquake. SSHAC Level 3 Workshop 1, Cape Town.

Saunders, I., Brandt M., Molea T., Akromah L. & Sutherland B. (2010). Seismicity of southern

Africa during 2006 with special reference to the Mw 7 Machaze earthquake. South African

Journal of Geology 113(4), 369-380.


Rayleigh-wave inversion and body-wave modelling. Geophysical Journal the Royal

Astronomical Society 83(3), 563-614.



340

Storchak, D. (2009). E-mail communication to M. Grobbelaar, dated 12 March 2009.

USGS (2011) http://earthquake.usgs.gov/earthquakes/eqarchives/epic/

Wagner, G.S. & Langston, C.A. (1988). East African earthquake body wave inversion with

implications for continental structure and deformation. Geophysical Journal, 94(3), 503-518.


341

Table 4.2. Data Evaluation Table 6.5. Focal Mechanism Solutions.




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

Brandt, M.B.C.

& Saunders, I.

New regional moment

tensors in South Africa

2011 Style of faulting

Time domain surface wave waveform

inversion technique was used to

derive moment tensor solutions,

moment magnitude and focal depth for

2 mine-related and 1 tectonic events.

The mining events studied are: the

25th September 1997 Far West Rand

and the 5th December 1998 Far West

Rand earthquakes. The tectonic event

studied is the 1999-02-04 Fauresmith,

in the Koffiefontein area.

The focal mechanisms derived from

the moment tensor inversion were:

The 25th September 1997 Far west

rand event: normal-type faulting

(strike1=354°, dip1=49° and rake1=-

86°, and strile2=167°, dip2=41° and

rake2=-95°). The seismic moment,

moment magnitude and focal depth

obtained were 1.55E+22dyne-cm, 4.1

and 2km, respectively.

The 5th December 1998 Far West

Rand event: normal-type with

strike1=296°, dip1=88° and

rake1=144°, and strile2=28°, dip2=54°

and rake2=3°. The seismic moment,



and 1km, respectively.

Q5: R5

The Team

used the

mechanis

m of the

tectonic

event to

assess

the style

of faulting

in the CK

source

zone for

the future

earthquak

e

characteri

stics.

Beside

the fact

that the

focal

plane

solution

was

obtained

using

moment

tensor

inversion

10

Sort by the criteria for identifying the seismic source: probability of activity, source/fault geometry, recurrence, Mmax, or future earthquake characteristics (rupture geometry, style of faulting, and seismogenic thickness). 11

Quality refers to the degree to which these particular data relate to and provide insights to the SSC model and can be used in its development . Quality (Q1=low; Q5=high) Reliance is the degree to which the data provide direct support and justification for particular elements/parameters of the SSC Mode. Reliance (R1=low, U5= high)


342




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness


event: normal-oblique type with two

nodal plane having (strike1=170°,

dip1=70°, and rake1=-25°, and

strike2=269°, dip2=66° and rake2=-

165°) . The first motion polarities

confirmed the moment tensor fault

plane solution which gives the

following solution: strike=164°, dip=70°

and rake=-53°. The seismic moment,



and 11km, respectively..


since the authors used both the

waveform inversion and polarities.

Information on moment tensor and

type of faulting is R5 since the events

is located in our source zones.

(good

method

and

relevant

method),

the

solution is

among

the few

focal

plane

solution

we have

in South

Africa.

The team

did not

use the

solution

for the

two

mining

events.

Bowers, D.

The October 30, 1994,

seismic disturbance in South

Africa: Earthquake or large

rock burst?


Bowers (1997) used broad-band

waveform data from the Global

Seismographic Network (GSN)

stations to invert for moment tensor

and depth of the event. Inversion of

the relative amplitudes of body and

surface waves at regional and

teleseismic and polarities (for clear

first P onset) yielded a normal-type

focal mechanism with strike=190°,

dip=45° and slip=-70°, and a scalar

Q5: R2

The Team

did not

use the

informatio

n for the

source

characteri

zation.


343




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

moment of 2.4E+16Nm. The fitting of

synthetic and observed seismograms

gave the best result for the depth of

2.3km.

The information on focal mechanism is

of quality Q5 since the full waveform

inversion method was used. But this

information was but not very relevant

R2 since the event was not tectonic

but mine-related. And the event itself

was not located in a particular source

zone.

Dziewonski, A.

M., Ekström,

G.,

Woodhouse,

J.H. & Zwart,

G.


solutions for October–

December 1986




event in Lesotho is given. For the

event, the estimated centroid depth is

15km, the moment is 1.29E+17dyne-

cm, Mw is 5.3, the fault solution is

pure normal fault with two nodal

planes having strike=168, dip=37 and

rake=-90, and strike=348°, dip=53°

and rake =-90°. The seismic moment,

moment magnitude and depth

obtained were 1.29E+17N-m, 5.3 and

15.0km, respectively.


since the authors used the centroid

moment tensor inversion to obtain the

style of fault. The focal mechanism is

also relevant Q5 since the event is

located in the CK zone.

Q5: R5

The team

used the

informatio

n on the

style of

fault to

identify

the range

of strike,

dip and

rake in

the CK

zone for

the future

earthquak

e

characteri

stics.


344




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

Dziewonski, A.

M., Ekström,

G.,

Woodhouse,

J.H. & Zwart,

G.


solutions for July–September

1990




mining event South Africa is listed. For

the event, the estimated centroid

depth is 28.3km, the moment is

3.58E+16dyne-cm, Mw is 5.3, the fault

solution is pure normal oblique fault

with two nodal planes having

strike=11, dip=45 and rake=-61, and

strike=153°, dip=52° and rake =-115°.

The seismic moment, moment

magnitude and depth obtained were

3.58E+16N-m, Mw=5.0 and 28.3km,

respectively.

The quality of this information on the

focal plane solutions is Q5 since the

authors used both the centroid

moment tensor inversion but the result

itself was not very relevant R1 since

the event is mining related.

Q1: R1

Although

of good

quality,

the focal

mechanis

m

informatio

n from

this event

was not

used for

the future

earthquak

e

characteri

stics.

Fairhead, J.D.

& Girdler,

R.W.

Seismicity of Africa 1971 Style of faulting

In this study the fault plane solution of

the Ceres earthquake is listed.

To derive the fault plane solution,

teleseismic first-motion polarities of P

and PKP phases were used. The

solution obtained indicates a strike-slip

style-of-faulting with two nodal planes

having the following strike and dip: (1)

131° and 82°SW, and (2) 42° and

82°N. The plane (1) was considered

as the fault plane which coincides with

Q4: R5

The team

used this

informatio

n for the

future

earthquak

e

characteri

stics in

the SYN

zone.


345




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

the distribution (with strike=120°) of

the associated aftershocks associated

(Green & Bloch, 1971). The event is


The quality of the information is Q4

since only first-motion polarities were

used. But the focal plane solution is

very relevant since the event is


Fairhead, J.D.

& Stuart, G.W.

The seismicity of the East

African rift system and

comparison with other

continental rifts


The fault plane solution of the 1st July

1976 Koffiefontein earthquake is

investigated among others. The event

is located in the CK zone.

First motion polarities of P phases

were used to determine a fault plane

solution of normal-type characterized

by E-W oriented tensional stress. The

two nodal planes obtained had the

following values: (1) strike=2° and

dip=70° and (2) strike=18° and

dip=20°.

These fault parameters are of quality

Q4 since only polarities and no

amplitude of phases were used for the

inversion. But these information were

relevant R5 since the event is located

in the CK zone.

Q4: R5

The team

used the

informatio

n to

determine

the range

of fault

parameter

s in the

CK for the

future

earthquak

e

characteri

stics.

Fan, G. &

Wallace, T.

Focal mechanism of a recent

event in South Africa: A

study using a sparse very

broadband network


Focal mechanism of the October 30,

1994 event (mb = 5.7) near the

.

Q5: R1

The team

did not


346




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

northwestern border of Orange Free

State in South Africa is obtained using

waveform fitting. The depth of the

event is 12km and the style of fault is

normal with strike=345, dip=14 and

rake=-105. Although the event was a

mining event, the focal depth obtained

is not consistent with a mining related

event (Bowers, 1997). The quality of

the fault plane solution is Q4 and the

relevance of R1 since the earthquake

is a mining related event. The focal

depth being consistent with mining

event, the quality for the depth and the

relevance are Q1 and R1,

respectively.

use the

event for

seismic

source

characteri

zation

since it is

a mining

event

Foster, A.N.,

and Jackson,

J.A

Source parameters of Large

African earthquake:

implications for crustal

rheology and regional

kinematics


The 29-09-1969 Ceres earthquake:

Using analogue body-waveform data

from the WWSSN stations and digital

data from the Global Digital

Seismograph Network (GSN), P- and

SH-waves inversion and waveform

fitting methods were used to

determine the focal mechanism, focal

depth, moment tensor and moment

magnitude of the 29th September

1969 Ceres event. Two pure strike-slip

possible solutions were obtained: (1)

strike=305°, dip=87° and rake=3° and

(2) strike=215°, dip=87° and

rake=177°. A seismic moment of

Q5: R5

The team

used the

focal

plane

parameter

s to

estimate

the range

of the

fault

parameter

s (strike,

dip and

rake) for

future

earthquak


347




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

3.9E+18Nm, moment magnitude of

Mw 6.4 and depth of 5km were

calculated.

The focal solution obtained for this

event is of quality Q5 since the

waveform inversion method was used,

and the relevance is R5 since the

event is located in the SYN zone.

e

characteri

stics in

the SYN

zone.

Green, W.E. &

McGarr, A.

A comparison of the focal

mechanism and aftershock

distribution of the Ceres,

South Africa earthquake of

September 29, 1969

1972 Style of faulting.

The fault plane solution was

determined from the first motion P-

wave polarities of long-period

seismograms of the Ceres (1969-09-

29) recorded by 42 World-Wide

Standardized Seismographic Network

(WWSSN) stations. The derived focal

mechanism showed that the nodal

plane identified as fault plane was of

strike N 39 ° W to N 43° W (Figure

6.8.2). And the fault type was a pure

strike-slip.


type of faulting is Q4 since only

polarities were used and the relevance

is R5 since the event was located in

the SYN zone.

Q4: R5

The

informatio

n was

used for

future

earthquak

e

characteri

stics in

the SYN

zone.

Jensen, B.L.






Using waveform inversion and

modeling of long period P- and SH-

waves, the focal mechanism, focal

Q5: R5

The team

used the

focal


348




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness


magnitude of the 01-07-1976

Koffiefontein earthquake are

determined. The result of the inversion

showed that the mechanism was a

pure normal fault with strike=308°,

dip=22° and rake=-86°. The focal


magnitude were 5.5km, 2.66E+24

dyne-cm and 5.8 respectively.


type of faulting and the focal depth are

Q5 since the waveform inversion and

fitting were used, and the relevance is

R5 since the event was located in the

CK zone.

plane

parameter

s to

estimate

the range

of the

fault

parameter

s (strike,

dip and

rake) for

future

earthquak

e

characteri

stics in

the CK

zone.

Krüger, F.,

Reichman, S.,

& Scherbaum,

F.

Moment tensor solution for

the 29.9.1969 Ceres

earthquake. SSHAC Level 3

Workshop 1, Cape Town.

2011 Style of Faulting

In this investigation of the Ceres

earthquake, moment tensor inversion

was done using scanned and digitized

seismograms from a set of WWSSN

stations operational in 1969. For the

estimate of the solution, body- and

surface waves were used. The best

double solution obtained yielded a

strike-slip (SSE-WNW) fault with

strike=305°, dip=78° and rake=1.2°

(Figure 6.8.7), with a centroid

depth=15km.

The focal mechanism obtained was

rated high quality and relevant. In fact,

the method used moment tensor

Q5:R5

The Team

used the

mechanis

m of this

Ceres

event to

assess

the style

of faulting

in the

SYN

source

zone for

future

earthquak


349




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

inversion and waveform fitting to

obtain focal mechanism and focal

depth. The focal solution obtained was

consistent with the mechanism

expected (strike-slip) in the SYN zone.

e

characteri

stics in

this zone.

Maasha, N. &

Molnar, P.

Earthquake fault parameters

and tectonics in Africa


Fault plane solution of 11 earthquakes

in Africa. It includes the 1969-09-29

Ceres earthquake showing a strike-

slip style of fault.

The mechanism and seismic moment

were determined using first motions

polarities, and P-wave spectra,

respectively. For P-wave spectra, the

Brune model (Brune, 1970) was used

for the calculation of seismic moment

and moment magnitude as listed in

EPRI94. The result showed that the

Ceres event mechanism was strike-

slip type with two nodal planes: (1)

strike=44° and dip=82° and (2)

strike=133° and dip 81° (Figure 6.8.3).

Seismic moment of 2.0E+25 dynes-cm

and moment magnitude of Mw 6.4 was

calculated.

The quality Q4 and the relevance R5

is attributed to the mechanism

obtained. Q4 can be explained by the

fact that only polarities were used and

R5 is attributed because the solution

obtained shows strike-slip mechanism

Q5: R3

The team

used the

fault

plane

parameter

s for the

future

earthquak

e

characteri

stics in

the SYN

zone.


350




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

expected in the SYN zone, which is

one of our seismic zone.

Mangongolo A.

CGS Unpublished

investigation


In an effort to add more focal plane

solution, six events were investigated:

the 1998-04-24 Augrabies event in

the Nam zone (Event 1), the 1998-06-

22 Three Sister event in the KAR zone

(Event 2), the 1998-09-06 Lesotho

earthquake in the CK zone (Event 3),

the 1998-10-05 Fraserberg event in

the CAR zone (Event 4), the 1999-02-

04 Koffiefontein event in the CK zone

(Event 5) and the 1999-07-03

Koffiefontein event in the CK zone

(Event 6).

Event 1:

The 24th April 1998 Augrabies

earthquake was located at 28.214°S

and 20.367°E. To derive the focal

mechanism, first-motion P-wave

polarities from the SASE stations were

used. Using FOCMEC, the solution

obtained is strike=138°, dip=90° and

rake=38°. While FPFIT gives the


and rake=18°. Both solutions obtained

yield a strike-slip fault-type. This

solution was of quality Q3 since only

polarities were used and the azimuthal

Q3:R4

Event 1

was used

for the

future

earthquak

e

characteri

stics in

the NAM

seismic

zone.

Event 2

and 4

were

used for

the future

earthquak

e

characteri

stics in

the KAR

seismic

zone.

Event 3, 5

and 6

located in

the CK


351




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

coverage was not the best. But the

solution was of relevant R4 since the

solution is amongst the few we have

for event in the NAM zone.

Event 2:

This event was located at the

coordinate 31.877°S 23.356°E. To

derive the focal solution, first-motion

P-wave polarities from the SASE

stations, were used The fault-type

mechanism shows an oblique-slip with

strike=19°, dip=41° and rake=-121°.

This solution is poor since most of the

stations used are situated north of the

event.

The quality for this solution is Q3 since

only polarities were used and the

azimuthal coverage was not the best.

But the solution was of relevant R4

since the solution is amongst the few

we have for event in the CAR zone.

Event 3:

The location of this event is at the

coordinate 30.255°S and 27.976°E.

First-motion P-wave polarities of

waveforms recorded at the SASE

stations, were used to obtain the focal

mechanism solution for this event. The

fault-type mechanism shows a normal-

type fault with strike=148°, dip=48°

and rake=-67°. The solution also looks

poor since only stations located north

of the event were used for the fault

plane solution. So quality Q2 was

allocated to it. Although the quality is

Q3, the relevance is R4 since the

zone was

used for

the future

earthquak

e

characteri

stics in

the CK

zone.


352




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

event is located in the CK zone and

the mechanism is consistent with other

mechanisms in the Lesotho area.

Event 4:

The 5th October 1998 Fraserburg


and 22.347°E. First-motion P-wave

polarities as recorded at SASE

stations were used to derive the focal

mechanism solution. Two computer

programs, FOCMEC and FPFIT were

used to determine the solution. Using

FOCMEC, the solution obtained was

strike=9°, dip=67° and rake=-19°,

while FPFIT gives the following

solution: strike=345°, dip=76° and

rake=-26°. Both solutions obtained


The quality Q3 was attributed to this

solution because only polarity data

were used. The relevance R4 was

given to the solution because this

solution is among the few solutions we

have in the CAR zone.

Event 5:


earthquake belongs to the

Koffiefontein earthquake cluster and

was located at 29.76°S and 25.70°E.

First-motion P-wave polarities as

recorded at SASE stations were used

to derive the focal mechanism

solution. The solution obtained was

strike=98°, dip=78° and rake=-121°.

This solution obtained yield a normal-

oblique fault-type.


353




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

Quality Q3 was allocated to it since

only polarity data were used. Although

the quality is Q3, the relevance is R4

since the solution is among the few

solutions we have in the CK zone.

Event 6:

This event belongs to the Koffiefontein

earthquake cluster and was located at

29.501°S and 25.171°E.

First-motion P-wave polarities as

recorded at SASE stations were used

to derive the focal mechanism solution

(Figure 6.8.25). The solution obtained

was strike=68°, dip=58° and rake=-

174°. This solution obtained yield a


Quality Q3 was attributed to this

solution since only polarity data were

used. And relevance R4 was given to

this solution because this solution is

among the few solutions we have in

the CK zone.

Saunders, I CGS unpublished

investigation


In an effort to add more focal plane

solution, 7 events were investigated:

the 2007-03-11 Leeu-Gamka event in

the KAR zone (Event 1), the 2010-11-

21 Augrabies event in the NAM zone

(Event 2), the 2010-12-25 Augrabies

in the NAM zone (Event 3), the 2010-

12-25 at 23h28’ in Augrabies event in

the NAM zone (Event 4), the 2010-12-

28 Augrabies event in the NAM (Event

5), the 2011-01-04 Augrabies event in

the NAM zone (Event 6) and the 2011-

Q5: R4 Q5: R5 Q3:R4

The styles

of faulting

for these

events

were

used for

the future

earthquak

e

characteri

stics in


354




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

12-18 Augrabies event in the NAM

(Event 7).

Event 1:

The location of this event is 32.834°S

and 22.081°E. First-motion P-wave

polarities as recorded by the South

Africa National Seismological Network

(SANSN) were used to derive the focal

mechanism. Two computer programs

FOCMEC and FPFIT were also used

to determine the solution (Figure

6.8.26). Using FOCMEC, the solution


rake=151°, while FPFIT gave the




Event 2:

The 21st November 2010 Augrabies

earthquake occurred at 28.684°S and

20.393°E. Using first-motion P-wave

polarities as recorded by the SANSN,

the focal mechanism solution was

obtained. Two computer programs

FOCMEC and FPFIT were used to

derive the solution (Figure 6.8.27).

Using FOCMEC, the solution obtained

is strike=21°, dip=52° and rake=18°,

while FPFIT gave the following


rake=28°. Both solutions obtained


Event 3:

This event occurred at 28.795°S and

20.507°E. Using first-motion P-wave

the NAM

and the

KAR

seismic

zones.


355




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

polarities as recorded by the SANSN

stations, the focal mechanism solution

was obtained. Two computer

programs FOCMEC and FPFIT were

used to derive the solution (Figure







Event 4:

The location of this event is 28.718°S

and 20.414°E. Using first-motion P-

wave polarities as recorded by the

SANSN stations, the focal mechanism

solution was obtained. Two computer









Event 5:

This event was located at 28.833°S

and 20.519°E. For the routine location,

first-motion P-wave polarities as

recorded by the SANSN stations

helped to derive the focal mechanism

solution (Figure 6.8.30) using two

computer programs: FOCMEC and

FPFIT. With FOCMEC, the solution




356




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness




Event 6:

This event was located at 28.781°S

and 20.491°E. Using first-motion P-

wave polarities as recorded by the

SANSN stations, the focal mechanism

solution was obtained. Two computer









Event 7:

The 18th December 2011 Augrabies


and 20.423°E.

Using first-motion P phase polarities

as recorded by the SANSN stations,

the focal mechanism solution was

obtained. Two computer programs,

FOCMEC and FPFIT were used to

derive the solution (Figure 6.8.32).

Using FOCMEC, the solution obtained

is strike=9°, dip=35° and rake=18°,

while FPFIT gave the following


rake=10°. Both solutions obtained


The quality of the information on focal

mechanism is Q3 because only

polarity data were used. And the


357




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

relevance is R4 since the fault

parameters are among the few we

have in the NAM and KAR zone.

USGS NEIC USGS PDE catalogue 2011 Style of faulting and seismogenic

depth

The information on the 18th December

2011 Augrabies earthquake located at

28.687°S and 20.423°E, was retrieved

from the ISC bulletin.

USGS used waveform inversion used

to determine the moment tensor

solution for this event. Seismic

moment, moment magnitude and focal

mechanism were then obtained. To

estimate the centroid focal depth,

synthetic seismograms were


seismograms. The result showed that

the mechanism was of strike-slip type

faulting (strike1=254°, dip1=78° and

rake1=-21°, and strile2=349°,

dip2=70° and rake2=167°) (Figure

6.8.33). The seismic moment, moment

magnitude and focal depth obtained

were 4.10E+16dyne-cm, 4.3 and

10km, respectively.

Quality Q5 was attributed to this

solution since ISC used moment

tensor inversion. And the relevance

given to this solution is R5 because

the solution is consistent with the

mechanism in the Augrabies area.

Q5: R5

The styles

of faulting

for these

events

were

used to

characteri

ze future

earthquak

e in the

NAM

zone.

Shudofsky,

G.N.


depths of East African


Q5: R5

.


358




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

earthquakes using Rayleigh-

wave inversion and body-

wave modeling

In this study, Rayleigh-wave waveform

inversion and body-wave waveform

modeling for some African

earthquakes are presented. The list

includes two earthquakes in South

Africa:

The 1969-09-29 Ceres and its 1970-

04-14 aftershock, and

the 1971-07-01 Koffiefontein

earthquakes.

The inversion yields a strike-slip focal-

mechanism (strike=310°, dip=82° and

slip=180°) and focal depth = 30km for

Ceres, a strike-slip mechanism

(strike=334, dip=74 and slip=160) and

focal depth = 10km for the Ceres

aftershock, and normal-oblique

faulting (strike=300, dip=63 and

slip=219) and depth = 6km for

Koffiefontein.

Quality Q5 and relevance R5 was

given to the fault parameters obtained

since waveform inversion method was

used and the events are located in the

SYN and the CK zones.

The styles

of faulting

for these

events

were

used for

future

earthquak

e

characteri

stics in

the SYN

and CK

zones.

Wagner, G.S.

& Langston,

C.A.

East African earthquake

body wave inversion with

implications for continental

structure and deformation


5 African earthquakes including the

1969-09-29 Ceres were investigated.

Waveform inversion and waveform

fitting method were used to determine

the mechanism and focal depth of this

event. Long-period WWSSN

Q5: R5

The team

used the

focal

plane

parameter

s for the


359




Probability of

Activity

Seismic Source or

Fault Geometry


Slip Rate/RI Mmax

Rupture Geometry

(strike, dip)

Style of

faulting

Seismogenic

Thickness

seismograms (recorded on 75cm film

chips) were digitized. Both P-wave

and SH-wave were used to obtain the

focal solution (Figure 6.8.5). The two

solutions derived using P-waves and

SH-waves showed a nearly pure

strike-slip fault: (1) strike of 124° and

dip of 88° and (2) a strike of 217° and

a dip of 89°. The focal depth

determined was 4km.

Q5 and R5 were attributed to the focal

plane solution because of the method

used and the location of the event

(SYN zone).

earthquak

e

characteri

stics in

the SYN

zone.



360

References



Brandt, M.B.C. (1997). Implementation of the SEISAN earthquake analysis software for the

SUN to analyze the data obtained through the South African National Seismograph Network.

Report CGS 1997-0263, Council for Geoscience, Pretoria, South Africa.


solutions for October–December 1986. Physics of the Earth and Planetary Interiors 48, 5–17.


solutions for July–September 1990. Physics of the Earth and Planetary Interiors 67, 211–220.

Fairhead, J.D., & Girdler, R.W. (1971). The Seismicity of Africa. Geophysical Journal 24(3),

271-301.

Fairhead, J.D., & Stuart, G.W. (1982). J.D. The seismicity of the East African rift system and

comparison with other continental rifts, In: Palmason, G. (Editor), Continental and Oceanic Rifts,

American Geophysical Union Geodynamic Series 8, 41–61.

Fan, G., & Wallace, T. (1995). Focal mechanism of a recent event in South Africa: A study using

a sparse very broadband network. Seismological Research Letters 66(5), 13-18.



422-448.

Green, W.E., & McGarr, A. (1972). A comparison of the focal mechanism and aftershock

distribution of the Ceres, South Africa earthquake of September 29, 1969. Bulletin of the



continental interior of Africa. MSc Thesis, Memphis State University.



361

Krüger, F., Reichmann, S., & Scherbaum, F. (2011). Moment tensor solution for the 29.9.1969

Ceres earthquake. Presentation at TNSP Workshop 1, April 2011.

Maasha, N., & Molnar, P. (1972). Earthquake fault parameters and tectonics in Africa. Journal

of Geophysical Research 77(29), 5731-5743.


Rayleigh-wave inversion and body-wave modeling. Geophysical Journal of the Royal


USGS (2011) http://earthquake.usgs.gov/earthquakes/eqarchives/epic/

Wagner, G.S., & Langston, C.A. (1988). East African earthquake body wave inversion with

implications for continental structure and deformation. Geophysical Journal 94(3), 503-518.


362

Table 4.3. Data Evaluation Table 6.7. Catalogue Declustering.




Seismogenic Probability

p[S] Fault

Geometry

Recurrence/ Recency & Slip Rate/RI Mmax

Rupture Geometry

(strike, dip) Style of Faulting


Ebel Analysis of aftershock and foreshock activity in stable continental regions: Implications for aftershock forecasting and the hazard of strong earthquakes

2009 Recurrence

• Determines Ohmori-law parameters for foreshock-aftershock sequences in SCRs, covering multiple regions. The data include the Ceres sequence and several other African earthquakes.

• Finds that these parameters are in good agreement with each other, as well as with the parameters determined for Southern California that are often used as default for the Reasenberg (1985) algorithm.

Q5/R1

Gardner & Knopoff

Is the sequence of earthquakes in Southern California, with aftershocks removed, Poissonian?

1974 Recurrence

• Window-based declustering algorithm originally developed for Southern California.

• Long-established and widely-used declustering method, shown to produce good results for many regions, as well as global catalogues.

• Shown to provide similar results to rate-thinning approaches for sparse catalogues (e.g. CEUS SSC)

• Examination of individual clusters and overall performance with Thyspunt catalogue shows a good performance of this algorithm, which is therefore adopted for declustering.

Q4/R5


363





p[S] Fault

Geometry


Rupture Geometry



Grünthal The up-dated earthquake catalogue for the German Democratic Republic and adjacent areas—Statistical data characteristics and conclusions for hazard assessment

1985 Recurrence

• Includes independently determined magnitude-dependent space and time windows for window –based declustering developed for Central Europe.

• Windows are almost identical to the Gardner & Knopoff (1974) windows and in consequence declustering results are extremely similar.

• Not used as an alternative declustering approach given the assessment that this would not really be a genuine alternative (same type of approach, i.e. window-based, and identical imported calibration).

• Reliance nevertheless high as results strongly supports universal/transportable nature of Gardner & Knopoff (1974) windows.

Q4/R4

Hainzl et al. Estimating background activity based on interevent-time distribution

2006 Recurrence

• Stochastic point-process simulations to classify events as mainshocks or aftershock and obtain non-parametric estimates of the background seismicity rate based on the inter-event time distribution.

• Not conditioned on magnitude, therefore the event designated as mainshock in a cluster is not necessarily the largest of the cluster. While this does not affect the performance of the method when applied to large datasets, this characteristic is likely to lead to issues in the case of a very sparse catalogue as considered here.

• Additionally, the method subdivides the data in subsets (magnitude bins). Given the very limited number of datapoints in the catalogue under consideration, this subdivision process hampers the determination of stable estimates.

• Therefore the method is not applied here due to data limitations; the assessment of the method itself as high-quality is not affected.

Q4/R2

Knopoff & Gardner

Higher seismic activity during local night on the raw worldwide earthquake catalog.

1972 Recurrence

• Study of statistics of seismicity leading to Gardner & Knopoff (1974) study

• Quality Q2 due to antiquated nature of data and limited relevance to the topic

• Study superseded by Gardner & Knopoff (1974)

Q2/R1

Luen & Stark Poisson tests of declustered catalogues

2012 Recurrence

• Statistical study using Southern Californian catalogue. The authors investigate the performance of various

Q2/R3


364





p[S] Fault

Geometry


Rupture Geometry



declustering techniques in terms of producing a spatially inhomogeneous, temporally homogeneous Poisson process (SITHP).

• The authors find that none of the techniques examined (including Gardner & Knopoff, 1974 and reasenberg, 1985) satisfy this hypothesis. Previous results to the contrary are attributed to deficiencies in the statistical tests used.

• Results are somewhat improved by relaxing the statistical criterion and replacing it by one of “conditionally exchangeable times”.

• The dependence on the conclusion of this article is low despite an undoubtedly very rigorous mathematical analysis, because the authors of the paper do not seem to consider the practical aspects of the application (and by their own admission are unfamiliar with the actual objectives of catalogue declustering). As a result, many of the points highlighted as statistical weaknesses are in fact properties desirable in seismic hazard applications (e.g., a relative insensitivity to fluctuations in the long-term rate, as well as to short-term fluctuations on the order of weeks). The Poissonian process providing their null hypothesis, which places a strong emphasis on spatial correlations, also bears little resemblance to the model used in seismic hazard analysis , which focuses essentially on the temporal distribution of events within a zone, regardless of their location within the zone, the spatial windows in declustering algorithms mainly serving the purpose of avoiding misassociation of independent events overlapping in time when larger zones are considered.

• While there is no reliance on the conclusions of th study, the raw data presented informs the assessment of the comparison of the Gardner & Knopoff (1974) and Reasenberg (1985) techniques by providing a second application example in addition to Van Stiphout et al. (2012).

Reasenberg Second-order moment of central Californian seismicity, 1969-1982.

1985 Recurrence

• Cluster-link based technique developed to investigate physical processes linking mainshocks and dependent events in central California.

• Focus of the study is more on physical processes, than on seismic hazard applications. Nevertheless, Reasenberg (1985) finds that the declustered catalogue is Poissonian in space and time. The technique subsequently became widely used for seismic hazard applications, probably due to the

Q5/R1


365





p[S] Fault

Geometry


Rupture Geometry



widespread availability of the code.

• This result is contradicted by more recent analyses using an extended catalogue for the same region (which in theory should have similar calibration parameters), as shown in Figure 1 of Van Stiphout et al. (2012), reproduced as figure 6.24 in the Thyspunt PSHA report. The cumulative number of events curve of the declustered catalogue clearly still features short-term noise (vertical steps), and overall the technique seems to keep more events in the declustered catalogue than other approaches leading to smoothly increasing cumulative number of events curves. Similar results can also be found in Luen & Stark (2012), again for a Californian catalogue.

• The analysis by Tibi et al. (2011) also points to a high sensitivity of this method to its multiple calibration parameters, in particular those characterising the catalogue (magnitude threshold, uncertainty estimate). The Ebel (2009) study points to the fact that the calibration of the Omori-law parameters is less likely to be an issue.

• The overall assessment of this technique is that this technique, while founded on sound physical bases, suffers from a strong sensitivity to its calibration parameters, which may lead to declustered catalogues that are non-Poissonian in nature through retention of events that are flagged as dependent by other techniques. This pattern of behaviour is expected to detrimentally affect the estimation of recurrence rates (bias towards small events). The difficulty of reproducing Reasenberg’s conclusions even when using Californian data also leaves little hope of a stable calibration with the sparse catalogue considered here, which is further more affected by significant uncertainties. The Reasenberg technique is therefore not applied here.


366





p[S] Fault

Geometry


Rupture Geometry



Shearer & Stark

Global risk of big earthquakes has not recently increased.

2012 Recurrence

• Study of large-magnitude (Mw ≥7.0) global seismicity using ISC and NEIC data with Mw determinations.

• Dataset biased towards active and subduction events due to its global nature.

• Moderate quality reflects the fact that objective of study is not the testing of declustering techniques and that the data is mostly from different tectonic regimes than that of interest.

• Find that catalogue declustered using a simple windowing technique is consistent with a Poisson hypothesis, whereas original non-declustered catalogue was not.

Q4/R3

Tibi et al. An alternative and efficient cluster-link approach for declustering of catalogues

2011 Recurrence

• Develop an extension to the Reasenberg (1985) cluster-link technique in which the time links are based on a simple magnitude-dependent function, instead of the Poissonian assumption.

• Discuss the limitations of the reasenberg (1985) approach, in particularity its sensitivity to calibration parameters such as the upper bound on the interaction time window.

• While their discussion of the calibration issues associated with the Reasenberg (1985) algorithm is useful, most of the limitations in terms of applying the method to a sparse catalogue remain. In particular, the method remains sensitive to catalogue-specific parameters such as the minimum cut-off magnitude, as well as location errors in terms of epicentral location and depth (which are significant in the case of the Thyspunt catalogue)

• The example applications shown (Slovenia and Middle East) are interesting because they correspond to much sparser catalogues than other applications based on Californian data. The authors include a residual analysis which supports their claim that their proposed approach leads to a closer fit with the Poissonian assumptions. However, this appears to be contradicted by the results shown in Figure 5 and 7, where the closest (visual) match to the Poissonian curve appears to be for the original (non-declustered) catalogue.

• While the technique is not assessed to be a viable declustering option for the Thyspunt catalogue, the discussion and results presented in this paper inform the selection of the Gardner & Knopoff (1974)

Q3/R2


367





p[S] Fault

Geometry


Rupture Geometry



algorithm as sole declustering alternative.

Uhrhammer Characteristics of northern and central California seismicity

1986 Recurrence

• Alternative magnitude-dependent windows for a window-based approached using Central and Northern Californian data.

• Windows are very different from Gardner & Knopoff (1974) windows, despite the good agreement of the latter with the windows independently determined for another region by Grünthal (1985).

• Visual examination of results individual clusters and overall performance with Thyspunt catalogue shows unsatisfactory performance (many obvious dependent events such as immediate aftershocks not removed).

• Therefore, this approach is not considered further as the calibration is assessed to be inappropriate for South Africa.

Q2/R1

USNRC Central and Eastern United States Seismic Source Characterization for Nuclear Facilities

2012 Recurrence

• Includes application of Veneziano & Van Dyck (1985) and Gardner & Knopoff (1974) technique to CEUS SSC catalogue

• Resulting numbers of independent events given by both approaches are very similar, which supports the finding that the Gardner & Knopoff (1974) windows can be applied outside of Southern California and provide a good estimate of long-term Poissonian rate.

Q3/R3

Van Stiphout et al.

Seismicity declustering. Community Online Ressource for Statistical Seismicity Analysis

2012 Recurrence

• Critical review of declustering techniques, including an application example to a large, high-quality catalogue.

• The comparison presented in their figure 1 (reproduced as Figure 6.24 in the Thyspunt PSHA report) showing that the Reasenberg technique does not produce a Poissonian declustered catalogue (wheras the Gardner & Knopoff algorithm and other approaches do) strongly weighed against the use of this technique.

• The results also support the good agreement between Gardner & Knopoff (1974) declustering and rate-thinning techniques (in this case, Zheng et al., 2002).

Q5/R5

Veneziano & Van Dyck

Statistical discrimination of aftershocks and their contribution to seismic hazard

1985 Recurrence

• Declustering technique based on rate-thinning applied to CEUS catalogue in EPRI94 study and later applied in USNRC (2012) CEUS SSC study.

Q5/R4


368





p[S] Fault

Geometry


Rupture Geometry



• Specifically developed for seismic hazard application, in particular the calculation of long-term Poissonian rates

• Shown in CEUS SSC (2012) to give very similar results to the Gardner & Knopoff (1974).

• Not used here as the very sparse nature of the catalogue might lead to calibration issues and/or numerical stability issues, whereas results from the more plentiful (but still sparse) CEUS SSC catalogue show that the results are similar to applying the windowing approach.

Wiemer ZMAP Software 2001 Recurrence

• Software used for Gardner & Knopoff (1974), Grünthal (1986) and Uhrhammer (1986) declustering algorithms

• Reasenberg (1985) algorithm also included in the sofftware but not used due to difficulty in determining a reliable calibration

• Software also used for completeness assessment using maximum curvature method and determination of regional b-value used as prior in recurrence calculations (see Section 6.8. Data evaluation table)

Q5/R5

Zhuang et al. Stochastic declustering of space-time earthquake occurrences

2002 Recurrence

• Stochastic technique to identify declustering events using a thinning operation for Poissonian point processes.

• Similar in nature to the Veneziano & Van Dyck (1985).

• Shown by Van Stiphout et al. (2012) to give a good agreement with the Gardner & Knopoff (1974) results for the same catalogue.

• Not used here for the same reasons related to data limitations.

Q5/R1



369

References

Ebel, J.E. (2009). Analysis of aftershock and foreshock activity in stable continental regions:

Implications for aftershock forecasting and the hazard of strong earthquakes, Seismological


Gardner, J.K., & Knopoff, L. (1974). Is the sequence of earthquakes in Southern California, with

aftershocks removed, Poissonian? Bulletin of the Seismological Society of the America 64(9),

1363-1367.

Grünthal G. (1985). The up-dated earthquake catalogue for the German Democratic Republic

and adjacent areas—Statistical data characteristics and conclusions for hazard assessment,

Proceedings 3rd International Symposium on the Analysis of Seismicity and Seismic Risk,

Czechoslovak Academy of Science, Prague, 19-25.

Hainzl, S., Scherbaum, F., & Beauval, C. (2006). Estimating background activity based on

interevent-time distribution, Bulletin of the Seismological Society of the America 96(1), 313-320.

Knopoff, L., & Gardner, J.K. (1972). Higher seismic activity during local night on the raw

worldwide earthquake catalog, GeophysicalJournal 28, 311-313.

Luen, B., & Stark, P.B. (2012). Poisson tests of declustered catalogues, Geophysical Journal


Reasenberg, P. (1985). Second-order moment of central Californian seismicity, 1969-1982,

Journal of Geophysical Research 90, 5479-5495.

Tibi, R., Blanco, J., & Fatehi, A. (2011). An alternative and efficient cluster-link approach for

declustering of catalogues, Seismological Research Letters 82(4), 509-518.

Uhrhammer, R.A. (1986). Characteristics of northern and central California seismicity (abs.),


USNRC (2012). Central and Eastern United States Seismic Source Characterization for Nuclear

Facilities.NUREG-2115, U.S. Nuclear Regulatory Commission, Washington D.C.

Van Stiphout, T., Zhuang, J., & Marsan, D. (2012).Seismicity declustering. Community Online

Ressource for Statistical Seismicity Analysis, doi:10:5078/corssa-52382934. Available at

http://www.corssa.org.



370

Veneziano, D. & Van Dyck, J. (1985). Statistical discrimination of aftershocks and their

contribution to seismic hazard: in Seismic Hazard Methodology for Nuclear Facilities in the

Eastern U.S., Volume 2, Appendix A-4, EPRI/SOG Draft 85-1.

Wiemer, S. (2001). A software package to analyze seismicity: ZMAP, Seismological Research

Letters 72, 373-382.

Zhuang, J., Ogata, Y., & Vere-Jones, D. (2002). Stochastic declustering of space-time

earthquake occurrences, Journal of the American Statistical Association 97, 369-380.


371

Table 4.4. Data Evaluation Table 6.8. Earthquake Catalogue Completeness.





p[S] Fault

Geometry


Rupture Geometry



Albarello & d’Amico

Detection of space and time heterogeneity in the completeness of a seismic catalog by a statistical approach: an application to the Italian area

2003 Recurrence

• Statistical approach investigating statistical fluctuations in the spatial and temporal distribution covered by a catalogue.

• The approach is assessed to be a viable option for high-quality, dense, long-span catalogues such as the Italian catalogue used in the study.

• However, it is not deemed to be a viable option for the Thyspunt catalogue due to the very limited number of data available, which preclude a meaningful interpretation of any statistically detected heterogeneities.

Q5/R1

Albini Investigating the past seismicity of the Eastern Cape Province

2012 Recurrence

• Provides the primary source of information for the completeness assessment of the historical part of the catalogue in the form of seismic histories at 12 observation points.

• Based on the assessment of positive and negative evidence in the documents pertaining to these locations, the historical record is assessed to be complete for the period ca. 1820-1936 for MMI VI-VII.

Q5/R5

Ambraseys & Adams

Reappraisal of major African earthquakes, south of 20°N, 1900-1930

1991 Recurrence

• Provides background information regarding seismic recording and likelihood of detection in sub-Saharan Africa during the first half of the 20th century.

• This information is considered in the determination of the probabilities of detection for the corresponding period.

Q5/R4

Bakun & Scotti

Regional intensity attenuation models for France and the estimation of magnitude and location of historical earthquakes

2006 Recurrence

• Provide the intensity prediction equation used for the determination of magnitudes from intensity point data fields using the Bakun & Wentworth (1997) technique implemented in the MEEP2 software.

• Used in the completeness analysis to estimate the areas over which an event could not have occurred

Q5/R4


372





p[S] Fault

Geometry


Rupture Geometry



without being felt with the threshold intensity of MMI VI at the privileged observation points of Albini (2012).

Beauval Analysis of uncertainties in probabilistic seismic hazard assessment: the example of France

2003 Recurrence

• Overview of available techniques for catalogue processing, illustrated with the example of France.

• A similar approach is followed in the Thyspunt catalogue analysis.

Q5/R3

Brandt Regional moment tensors, moment magnitude, completeness and national network expansion

2011 Recurrence

• Presentation about various aspects of the SANS, including a completeness analysis of the whole network.

• The magnitude of completeness found using the maximum curvature approach, Mc ~ 1.9, corroborates the values found from the analysis of the modern instrumental subset of the Thyspunt catalogue.

Q4/R4

Gane & Oliver South African earthquakes - 1949 to December 1952

1953 Recurrence

• Present the catalogue of events recorded by the Geological Survey network 1949-1952.

• These data contribute to the completeness analysis through an examination of the events successfully located by the network (e.g. northern Botswana event of 1952, for which the South African network location and magnitudes are very close to the teleseismic determinations), as well as those for which the South African recordings on their own are inconclusive.

• This information is used in the assessment of the probabilities of detection for the relevant period.

Q5/R4

Johnston et al. The Earthquakes of Stable Continental Regions

1994 Recurrence

• Presents the method involving equivalent periods of completeness (based on probability of detection) implemented in EPRI94 and later in the CEUS SSC study.

• The original method calls for subdivision of the individual seismic source zones into subzones reflecting different completeness levels. In view of the limited amount of data available, further

Q5/R4


373





p[S] Fault

Geometry


Rupture Geometry



subdivisions of the datasets corresponding to the single source zones was found to be undesirable for numerical stability reasons. Given that the spatial patterns of completeness were found to be broadly similar (at the resolution level allowed by the data) for relatively broad regions in the onshore portion of the study area, the method was applied in simplified form with a single “completeness zone” per source zone. The probabilities of detection assigned were thus assessed as the spatially averaged values for each zone.

• Due to the lack of information regarding completeness of moderate events in the offshore area forming part of the source zone ECC, this approach was supplemented by a completeness scaling factor to be applied to this zone.

Oliver South African earthquakes – January 1953 to December 1955

1956 Recurrence

• Presents the catalogue of events recorded by the Geological Survey network 1953-1956.

• Same usage for completeness analysis as the Gane & Oliver (1953) data.

Q5/R4

Saunders et al.

The South African National Seismograph Network

2008 Recurrence

• Presents an overview of the South African Seismic Network, which is used to inform the assessment of probabilities of detection for the relevant period.

Q5/R4

Schorlemmer & Woessner

Probability of detecting an earthquake

2008 Recurrence

• Present a statistical method to assess probability of detection at a network of stations, based on single-station calibrations using data from previous events. These single-station detection thresholds are then combined to map magnitude of detection across the region.

• One advantage of this approach is that it works equally well with sparse networks. However, the approach requires a large amount of calibration data (currently not readily available). Application in South Africa is further hampered by the frequent updating and reshuffling of the network (i.e., few stations have been in the same location with the same instrumentation), which, combined with the low level of seismicity, limits the availability of sufficient data for a robust calibration of the

Q5/R3


374





p[S] Fault

Geometry


Rupture Geometry



approach.

• Therefore, the approach was assessed as being too sophisticated for meaningful implementation with the data currently available. Even if it were attainable, the final result of the approach (a map of magnitude of detection) being of far higher spatial resolution than any other completeness assessment possible, would eventually be averaged spatially for the final assessment of probability of detection. In the light of these considerations, the spirit of the approach has been retained to inform the determination of the probability of detection values, albeit in a more quantitative manner due to the limitations of the data.

Stepp Analysis of completeness of the earthquake eample in the Puget Sound area and its effect on statistical estimates of earthquake hazard

1972 Recurrence

• Proposes a statistical method to detect changes in completeness in the form of breaks in the slope of the cumulative number of earthquake curve accumulated from the end of the catalogue.

• Used to inform and corroborate the periods of completeness determined from historical considerations as well as information regarding the development of instrumental networks.

Q5/R4

Stucchi et al. Assessing the completeness of Italian historical earthquake data

2009 Recurrence

• Presents an overview of the historical approach to assessing completeness, which considers the availability and likelihood of survival of earthquake reports, in the light of both positive and negative evidence.

• This approach was implemented in the Thyspunt study via the historical assessment of completeness in Albini (2012), which was later incorporated in the determination of the probabilities of detection.

Q5/R5


2012 Recurrence

• Presents the application of the probability of detection approach to completeness to the CEUS SSC catalogue.

• The full approach involves a data-driven assessment of the probability of detection

Q5/R4


375





p[S] Fault

Geometry


Rupture Geometry



approach using a maximum-likelihood approach. This was replaced here by a more qualitative assessment of the average probability of detection for each source zone, in view of the fact that the qualitative information (historical assessment,

Wiemer A software package to analyze seismicity: ZMAP

2001 Recurrence

• Software used for completeness assessment instrumental subset of the data available digitally, (i.e since 1997) using maximum curvature method, as well as determination of regional b-value used as prior in recurrence calculations.

• This analysis indicated Mc ~2.0 from 1997, Mc ~ 1.9 from 2003, and Mc 1.8 from 2007. These results are consistent with those found by Brandt (2011) for the whole network.

• This information was used to inform the probability of detection values assigned for the relevant period.

Q5/R4

Wiemer & Wyss

Minimum magnitude of complete reporting in earthquake catalogs: examples from Alaska, the Western United States, and Japan

2000 Recurrence

• Presents the maximum curvature approach used to determine the magnitude of completeness for the more recent instrumental data (1997-2011)

• The results were used to inform the probability of detection values assigned for the relevant period.

Q5/R4

Woessner & Wiemer

Assessing the quality of earthquake catalogues: estimating the magnitude of completeness and its uncertainty

2005 Recurrence

• Discusses pros and cons of the various approaches for statistical determination of the magnitude of completeness linked to the maximum curvature approach.

• This information was used to inform the determination of the magnitude of completeness for the more recent instrumental data (1997-2011)

• The results were used to inform the probability of detection values assigned for the relevant period.

Q5/R4

Willemann Regional Thresholds of the ISC Bulletin

1999 Recurrence

• Provides a study of regional variations of the completeness threshold of the ISC bulletin.

Q5/R4


376





p[S] Fault

Geometry


Rupture Geometry



• Gives a value of mb = 4.3 for the African region; this is used, along with other information, to set the completeness threshold at Mw 4.5 from the establishment of the WWSSN in 1964

Wright & Fernandez

Chapter 79.48: South Africa

2003 Recurrence

• Presents an overview of the history of seismic monitoring in South Africa, which is used to inform the assessment of probabilities of detection for the relevant period.

• A few slight inconsistencies with archive materials have been corrected in this assessment, hence the level of reliance is assessed as moderate.

Q4/R3

1 Sorted by the criteria for identifying the seismic source: probability of activity, source/fault geometry, recurrence, Mmax, or future earthquake characteristics (rupture geometry, style of faulting, and seismogenic thickness).

2 Quality refers to the degree to which these particular data relate to and provide insights to the SSC model and can be used in its development. Quality (Q1 = low; Q5 = high)

3 Reliance is the degree to which the data provide direct support and justification for particular elements/parameters of the SSC Mode. Reliance (R1 = low, R5 = high)



377

References

Albarello, D., Camassi, R., & Rebez, A. (2001). Detection of space and time heterogenereity

in the completeness of a seismic catalog by a statistical approach: an application to the

Italian area, Bulletin of the Seismological Society of America 91(4), 1694-1703.

Albini, P. (2012). Investigating the Past Seismicity of the Eastern Cape Province, South

Africa, Report No. 2012-0099, Rev. 0, Council for Geoscience, Pretoria, South Africa, 453 pp.

Ambraseys, N.N. & Adams, R.D. (1991). Reappraisal of major African earthquakes, south of

20°N, 1900-1930, Natural Hazards 4, 389-419.

Bakun, W.H. & Scotti, O. (2006). Regional intensity attenuation models for France and the

estimation of magnitude and location of historical earthquakes, Geophysical Journal


Beauval, C. (2003). Analysis of uncertainties in probabilistic seismic hazard assessment: the

example of France. PhD Thesis, Université Joseph Fourier, Grenoble, France [in French].

Brandt, M.B.C. (2011). Regional moment tensors, moment magnitude, completeness and

national network expansion. Presentation at TNSP Workshop 1, April 2011.

Gane, P.G., & Oliver, H.O. (1953). South African earthquakes – 1949 to December 1952,

Transactions of the Geological Society of South Africa 56, 21-33, Plates III-IV.

Johnston, A.C., Coppersmith, K.J., Kanter, L.R., & Cornell, C.A. (1994). The Earthquakes of

Stable Continental Regions, Final Report submitted to Electric Power Research Institute

(EPRI).

Oliver, H.O. (1956). South African earthquakes – January 1953 to December 1955,


Richter, C.F. (1935). An instrumental earthquake scale, Bulletin of the Seismological Society

of America 25, 1-32.

Saunders, I., Brandt, M., Steyn, J., Roblin, D., & Kijko, A. (2008). The South African National

Seismograph Network, Seismological Research Letters 79(2), 203-210.

Schorlemmer, D., & Woessner, J. (2008). Probability of detecting an earthquake, Bulletin of

the Seismological Society of America 98(5), 2103-2117.



378

Stepp, J.C. (1972). Analysis of completeness of the earthquake eample in the Puget Sound

area and its effect on statistical estimates of earthquake hazard, Proceedings of the

Microzonation Conference University of Seattle, Washington: Vol. 2, 897-909.

Stucchi, M., Albini, P., Mirto, C., & Rebez, A. (2009). Assessing the completeness of Italian

historical earthquake data, Annali di Geofisica 47(2-3), 659-673.

USNRC (2012). Central and Eastern United States Seismic Source Characterization for

Nuclear Facilities, NUREG-2115, U.S. Nuclear Regulatory Commission, Washington D.C.

Wiemer, S. (2001). A software package to analyze seismicity: ZMAP, Seismological

Research Letters 72, 373-382.

Wiemer, S., & Wyss, M. (2000). Minimum magnitude of complete reporting in earthquake

catalogs: examples from Alaska, the Western United States, and Japan, Bulletin of the


Willemann, R.J. (1999). Regional thresholds of the ISC Bulletin, Seismological Research

Letters 70(3), 313-321.

Woessner, J., & Wiemer, S. (2005). Assessing the quality of earthquake catalogues:

estimating the magnitude of completeness and its uncertainty, Bulletin of the Seismological


Wright, C. & Fernández, L.M. (2003). Chapter 79.48: South Africa. In: Lee, W.H.K., H.

Kanamori & P.C. Jennings (eds.), International Handbook of Earthquake and Engineering

Seismology. International Geophysics 81(B), 1433-1434.


379

Table 4.5. Data Evaluation Table 8.2. Global Assessments and Methodologies





p[S] Fault

Geometry


Rupture Geometry



Anderson Estimating Seismicity from Geological Structures for Seismic Risk Studies

1979 Recurrence

• Provides a methodology for translating fault slip rate into seismic moment rate by incorporating the seismogenic fault area

• Formulation is not relied upon because it is based on an exponential magnitude-frequency model, which is assessed to not be appropriate for faults

Q4/R3

Bate & Malan Tectonostratigraphic Evolution of the Algoa, Gamtoos and Pletmos Basins, Offshore South Africa

1992 Seismogenic Probability

• Seismic profile on Fig. 2 shows Gamtoos Fault dying out in Tertiary section, overlain by unfaulted upper unit.

Fault Geometry

• Seismic data suggest that the Gamtoos is a single discrete fault plane, but it is possible that it is a segmented fault zone comprising the Gamtoos and Elandsberg Faults (like what is observed onshore).

Q3/R4 Q 4/R4

Clark et al. Australia’s seismogenic neotectonic record: A case for heterogeneous intraplate deformation

2011 Recurrence

• Provides a compilation of evidence of temporal clustering for SCR faults

• SCR data regarding the number of events that occur within temporal cluster and ratio of the within-cluster intervals to the out-of-cluster intervals

• Used to interpret the recurrence history of the Kango fault and to make an assessment of temporal clustering

Q5/R4

Collettini & Sibson

Normal faults: normal friction?

2001 Rupture Geometry

• Provides a compilation of the dip of coseismic normal faults as determined by reliable focal mechanisms and aftershocks

• Used to develop generic fault dip distribution for virtual faults in source zones that are assessed to be normal faults, or fault sources whose downdip geometry is not well-constrained

Q4/R4 Q4/R4

Gutenberg & Richter

Earthquake magnitude, intensity, energy and acceleration

1956 Recurrence

• Provides basic exponential form to the magnitude-frequency relationship for source zones

Q2/R2


380





p[S] Fault

Geometry


Rupture Geometry



Hanks & Kanamori

A moment magnitude scale

1979 Recurrence

• Provides basic relationship that can be used to translate seismic moment to moment magnitude; used to translate fault slip rate and rupture geometry into a seismic moment rate

• Seismic moment rate becomes fault-specific recurrence using an applicable magnitude-frequency model

Q4/R4

Jackson & White

Normal faulting in the upper continental crust: observations from regions of active extension


• Provides a compilation of a number of coseismic normal faulting earthquakes

• Used to develop generic fault dip distribution for virtual faults in source zones that are assessed to be normal faults, or fault sources whose downdip geometry is not well-constrained

Q3/R2 Q3/R2

Johnston et al. The Earthquakes of Stable Continental Regions

1994 Mmax

• Provides definition of stable continental regions (SCR) based on geologic and tectonic criteria

• Developed Bayesian approach to assessing Mmax using worldwide data set of SCR regions and seismicity catalogue

• Prior distributions updated in CEUS SSC project (USNRC, 2012a) using the Johnston et al. approach.

• High reliance on approach, but prior distributions and SCR catalogue comes from CEUS SSC update

Recurrence

• Approach described in Johnston et al. (1994) is followed to calculate maximum likelihood estimates of the α(m0) and β parameters that are conditional on Mmax, for seismic source zones

Q5/R4 Q5/R3


381





p[S] Fault

Geometry


Rupture Geometry



Kijko Estimation of the maximum earthquake magnitude, mmax

2004 Mmax

• Presents a methodology for assessing the Mmax of seismic source zones within SCRs

• The approach requires significant numbers of earthquakes to have sufficient stability for application at the source zone level; thus, it is given low weight for the source zones in the Thyspunt PSHA

Q4/R3

Kijko On Bayesian procedure for maximum earthquake magnitude estimation

2012 Mmax

• Presents a criticism of the Bayesian approach to assessing Mmax with SCR regions, purporting that the Bayesian approach uses the mode of the posterior distribution as the estimate of Mmax for purposes of PSHA

• Criticism was refuted in CEUS SSC report (USNRC, 2012a) and this report

• Statement is made without support that mean Mmax is biased to large values: studies done in CEUS SSC project (USNRC, 2012a) show that mean Mmax is not biased

• Low quality rating is due to mis-representation of the use of the Bayesian approach to define a single estimator of Mmax.

Q1/R1

Kijko et al. Probabilistic PGA and spectral acceleration seismic hazard maps for South Africa [abstract]

2009 Mmax

• same as Kijko (2012)

Q1/R1

Klose & Seeber

Shallow seismicity in stable continental regions

2007 Seismogenic Thickness

• Defines a number of focal depth distributions for SCRs that have high-resolution earthquake focal depths

• Identify regions that have bi-modal depth distributions and uni-modal distributions

• Provides a basis for developing a depth distribution for the Thyspunt region and for testing whether or not the region shows evidence of depths below 20km, thus defining a bi-model distribution

Q5/R3

Leonard Earthquake fault scaling: Self-consistent relating of


• Defines a relationship between moment magnitude

Q4/R4 Q4/R5


382





p[S] Fault

Geometry


Rupture Geometry



rupture length, width, average displacement, and moment release.

and rupture length for SCRs, which is used in the hazard analysis to define the lengths of ruptures on virtual faults for given moment magnitudes

Mmax

• Used along with other empirical relationships to assess the magnitude associated with fault ruptures having particular lengths

• Is particularly applicable to SCR faults, although there are relatively few data to constrain the relationships; hence, standard deviations must be assessed using other relationships

NAGRA Probabilistic Seismic Hazard Analysis for Swiss Nuclear Power Plant Sites

Rupture Geometry

• Presents a weighting scheme whereby the distribution of future moderate-to-large earthquake focal depths is defined by multiplying the focal depth distribution for small-magnitude earthquakes.

• The Team assesses the lower fraction T which restricts allowable hypocentre positions to the lower fraction T of the downdip width of the rupture plane, assuming a uniform distribution of hypocentres within the allowable fraction.

Q4/R5

Petersen et al. Documentation for the 2008 Update of the United States National Seismic Hazard Maps

2008 Recurrence

• Provides an example of a community-based PSHA that uses the characteristic earthquake magnitude-frequency distribution of Youngs & Coppersmith (1985)

Q4/R3

Tanaka Geothermal gradient and heat flow data in and around Japan (II): Crustal thermal structure and its relationship to seismogenic layer

2004 Seismogenic Thickness

• Correlated the depth above which 90% of high-resolution earthquake focal depths lie (D90) with

~350° isotherm, thus proposing to use D90 as a meaningful estimate of the base of the seismogenic layer

• The D90 provides a tool for assessing the base of the seismogenic layer for regions having good-quality focal depths; in South Africa there are few such data, but the available data can be considered in drawing analogies to other tectonic regions

Q5/R3

Tanaka & Ito Temperature at the base of the seismogenic zone

2002 • (see Tanaka 2004 above)


383





p[S] Fault

Geometry


Rupture Geometry



and its relationship to the focal depth of the western Nagano Prefecture area

Tinti & Mulargia

Effects of magnitude uncertainties on estimating the parameters in the Gutenberg-Richter frequency-magnitude law

1985 Recurrence

• Identified that uncertainty in the estimated earthquake magnitudes can lead to bias in the estimated recurrence rate due to the exponential nature of the numbers of earthquakes of various magnitude

• Uncertainties can be accounted for, but the bias correction to account for exponentiality cannot be implemented for zones with very few earthquakes

Q4/R1


2012 Recurrence

• Developed conceptual model for including temporal clustering behavior into SSC model logic tree; whereby the fault is either within a cluster or out of a cluster, with both being characterized by a Poisson rate

Mmax

• For the Bayesian Mmax approach, developed new prior distributions for MESE and NMESE regions based on update and analysis of the global SCR earthquake catalogue

• Developed a weighting scheme for the Bayesian and Kijko Mmax approaches that incorporates measures of statistical stability due to numbers of earthquakes within the zone of interest

• Provided a rebuttal to criticisms lodged by A. Kijko of the Bayesian approach


• Developed and used the notion of the base of the

seismogenic layer being defined by ~350° isotherm and D90 cutoff of seismicity

• Developed focal depth distribution for entire CEUS consisting of high-resolution focal depths; in lieu of high-quality focal depth distributions in Thyspunt region, the CEUS distribution is used and checked by the available focal depth information in the region

Q5/R3 Q5/R5 Q5/R5


384





p[S] Fault

Geometry


Rupture Geometry



Wells & Coppersmith

New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement

1994 Mmax

• Empirical relationships used to develop assessment of Mchar for fault sources based on estimates of rupture length, rupture area, and displacement per event

• Relationships were developed using primarily data for earthquakes within active tectonic regions

Rupture Geometry

• Standard deviation for rupture length empirical regressions used to assess the standard deviation for the Leonard SCR rupture length relationship, which is used to assess rupture length for a given magnitude associated with virtual faults

Q4/R4 Q4/R4

Wesnousky Earthquakes, Quaternary faults, and seismic hazard in California

1986 Recurrence

• Develops the “maximum moment” magnitude-frequency relationship, which is focused specifically on individual faults; the distribution of magnitudes seen in earthquake recurrence curves is said to be the result of a distribution of fault lengths

• The model does not explain the occurrence of small-magnitude earthquakes that appear to be associated with individual faults, other than to postulate that they are associated with smaller faults

Q3/R3

Wheeler Methods of Mmax Estimation East of the Rocky Mountains

2009 Mmax

• Provides a review of methods for estimating Mmax for PSHA within SCR tectonic environments, such as the CEUS

• Concludes that statistical methods suffer from lack of data; analogue approaches such as the Bayesian approach of Johnston et al. (1994) show the most promise

• Confirms the applicability of the Bayesian approach for application with SCR regions, but no specific guidance is provided regarding the elements of preferred models or how they should be applied to seismic source zones

Q4/R2

Youngs & Coppersmith

Implications of fault slip rates and earthquake recurrence models to

1985 Recurrence

• Provides a model and formulation for a fault-

Q5/R5 Q4/R4


385





p[S] Fault

Geometry


Rupture Geometry



probabilistic hazard estimates

specific magnitude-frequency distribution that incorporates both the recurrence for a characteristics earthquake, Mchar, and an exponential component defining the recurrence of smaller-magnitude earthquakes

• Model is specifically developed to use input from fault slip rate, recurrence intervals from paleoseismic data

Mmax

• Proposes a boxcar distribution for magnitude of characteristic earthquake, Mchar, that is plus or minus one-quarter magnitude unit from expected value

Youngs et al. A comprehensive seismic hazard model for the San Francisco Bay region

1995 Recurrence

• Provides a justification for the shape of the characteristic earthquake model of Youngs & Coppersmith (1985), based on several faults in the San Francisco Bay area having high-quality slip rate and seismicity data

Q5/R3



3 Reliance is the degree to which the data provide direct support and justification for particular elements/parameters of the SSC Mode. Reliance (R1 = low, U5 = high)



386

References

Anderson, J.G. (1979). Estimating seismicity from geological structures for seismic risk

studies, Bulletin of the Seismological Society of America 69, 139-158.

Clark, D., McPherson, A. & Collins, D.C.N. (2011). Australia’s seismogenic neotectonic

record: A case for heterogeneous intraplate deformation, Record 2011/11. Geoscience

Australia, Canberra.

Collettini, C. & Sibson, R.H. (2001). Normal faults: normal friction? Geology 29, 927–930.

Gutenberg, B., & Richter, C.F. (1956). Earthquake magnitude, intensity, energy and

acceleration, Bulletin of the Seismological Society of America 46, 105-145.


Research 84, 2348–2350.Hanson, K.L., Slack, C., & Coppersmith, R. (2012b). Thyspunt



Jackson, J.A., & White, N.J. (1989). Normal faulting in the upper continental crust:

observations from regions of active extension. Journal of Structural Geology 11, 15-36.

Johnston, A. C., K. J. Coppersmith, L. R. Kanter, & C. A. Cornell (1994). The Earthquakes of

Stable Continental Regions, Five vols., Report for Electric Power Research Institute (EPRI),

Palo Alto, CA, EPRI TR-102261.

Kijko, A. (2004). Estimation of the maximum earthquake magnitude, mmax, Pure and

Applied Geophysics 161, 1-27.

Kijko, A. (2012). On Bayesian procedure for maximum earthquake magnitude estimation,

Research in Geophysics 2, 46-51.

Kijko, A., Graham, G., Singh, M., Roblin, D., & Brandt, M.B.C. (2009). Probabilistic PGA and

spectral acceleration seismic hazard maps for South Africa [abstract]: Invited lecture,

Workshop R1 ―Earthquake Hazard, the IASPEI General Assembly in Cape Town, January

11-16.



387

Klose, C.D., & Seeber, L. (2007). Shallow seismicity in stable continental regions,



average displacement, and moment release, Bulletin of the Seismological Society of

America 100, 1971–1988.

NAGRA (Nationale Genossenschaft für die Lagerung radioaktiver Abfälle) (2004).

Probabilistic Seismic Hazard Analysis for Swiss Nuclear Power Plant Sites (PEGASOS

Project), Volume 1, Final Report, Wettingen, Switzerland, July 31.

Petersen, M.D., Frankel, A.D., Harmsen, S.C., Mueller, C.S., Haller, K.M., Wheeler, R.L.,

Wesson, RL., Zeng, Y., Boyd, O.S., Perkins, D.M., Luco, N., Field, E.H., Wills, C.J., &

Rukstales, K.S. (2008). Documentation for the 2008 Update of the United States National

Seismic Hazard Maps, U.S. Geological Survey Open-File Report 2008–1128.

Tanaka, A. (2004). Geothermal gradient and heat flow data in and around Japan (II): Crustal

thermal structure and its relationship to seismogenic layer, Earth, Planets Space 56, 1195-

1199.

Tanaka, A., & Ito, H. (2002). Temperature at the base of the seismogenic zone and its

relationship to the focal depth of the western Nagano Prefecture area, Journal of the

Seismological Society of Japan 55, 1-10.

USNRC (2012a). Central and Eastern United States Seismic Source Characterization for

Nuclear Facilities, NUREG-2115, US Nuclear Regulatory Commission, Washington D.C.

Wells, D. L., & Coppersmith, K.J. (1994). New empirical relationships among magnitude,

rupture length, rupture width, rupture area, and surface displacement, Bulletin of the

Seismological Society of America 84, 974–1002.

Wesnousky, S.G. (1986). Earthquakes, Quaternary faults, and seismic hazard in California,

Journal Geophysical Research 91, 12587-12631.



388

Wheeler, R.L. (2009). Methods of Mmax Estimation East of the Rocky Mountains, U.S.

Geological Survey Open-File Report 2009-1018, 1-44.

Youngs, R.R., & Coppersmith, K.J. (1985). Implications of fault slip rates and earthquake

recurrence models to probabilistic hazard estimates, Bulletin of the Seismological Society of

America 75, 939-964.

Youngs, R.R., Coppersmith, K.J., Taylor, C.L., Power, M.S., DiSilvestro, L.A., Angell, M.L.,

Hall, N.T., Wesling, J.R., and Mualchin, L. (1992). A comprehensive seismic hazard model

for the San Francisco Bay region. In: Borchardt, G. and others (eds.), Proceedings of the

Second Conference on Earthquake Hazards in the Eastern San Francisco Bay Area.

California Department of Conservation, Division of Mines and Geology Special Publication

113, 431-441


389

Table 4.6. Data Evaluation Table A8.3.1. Extended Continental Crust Source Zone (ECC)


Use for SSC (Quality2/Reliance

3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry




1992 Seismic Source

• This paper summarizes the evolution of the offshore Mesozoic basins.

• These basins developed following reactivation of Late Precambrian and Palaeozoic structures as the result of extension associated with the Jurassic break-up of Gondwana.

Style of Faulting

• Report dip-slip and limited strike-slip movement on the curved Gamtoos Fault.

Q3/R2 Q3/R2

Barnett et al. Stratigraphy of the Upper Neoproterozoic Kango and Lower Paleozoic Table Mountain Group of the Cape Fold Belt Revisited

1997 Seismic Source

• Paper provides a description of the lithostratigraphy of the pre-Cape Kango Group, which is divided into Goegamma and Kansa subgroups (latter assigned to the base of the Cape Supergroup).

Q3/R1

Beattie Report of a Magnetic Survey of South Africa

1909 Seismic Source

• First report of a positive magnetic anomaly in the interior of the Western and Eastern Cape provinces.

Q2/R2

Ben-Avraham et al.

Early Tectonic Extension Between the Agulhas Bank and the Falkland Plateau due to the Rotation of the Lafonia Microplate

1993 Seismic Source

• The Agulhas Fracture Zone bounds the steep southeastern continental margin of South Africa

• Concave fault systems of the Pletmos, Gamtoos and Algoa Basins are similar to circles centered on the proposed Lafonia-Africa (LAF-AFR) Euler pole.

Style of Faulting

• They consider the curved structures exhibited by the large fault systems to be Middle Jurassic structures with a left-lateral strike-slip component, being the result of right-lateral 'drag' along the AFZ between South American (SAM) and Africa plates, rather than being an inherited Cape Fold Belt structures.

Q3/R2 Q3/R4

Ben-Avraham et al.

Structure and Tectonics of the Agulhas-Falkland Fracture Zone

1997 Seismic Source

• The 1,200 km long AFFZ is divided into four distinct sections: Mallory Trough, Dias Ridge, East London segment, Durban segments.

• Each segment differs from the others in its physiography and in the nature of the continent-ocean crustal boundary.

• Dias Marginal Ridge is a sub-cropping ridge that bounds the Southern Outeniqua Basin along most of its southern

Q4/R4


390



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



margin and separates it from the Agulhas Fracture Zone.

Booth & Shone Complex Thrusting at Uniondale, Eastern Sector of the Cape Fold Belt, Republic of South Africa: Structural Evidence for the Need to Revise Lithostratigraphy

1999 Rupture Geometry & Style of Faulting

• South-dipping normal faults are interpreted to be Mesozoic in age, having formed during an extensional phase related to the break-up of Gondwana.

Q3/R2 Q3/R3 Q3/R3

Bremner & Malan

Coastal Zone Morphology and Geology: Hermanus

1990 Seismic Source

• Map showing a series of conjugate northeast and northwest-striking dextral strike-slip faults near Hermanus in the “syntaxis domain”.

Q4/R4

Broad et al. Geology of the Offshore Mesozoic Basins

2006 Seismic Source

• Describe South Africa's continental margins to be a direct consequence of the break-up and separation of the West Gondwana supercontinent. Supercontinental break-up, initiated by extensional forces, commenced in the early Mesozoic. Separation by continental drifting began in the Early Cretaceous and is still continuing today.

• Outeniqua Basin is situated of the southern tip of Africa and bounded by the Columbine-Agulhas Arch to the W, the Port Alfred Arch to the east and the Diaz Marginal Ridge to the south.

• Outeniqua Basin comprises a series of rift subbasins including the Bredasdorp, Pletmos, Gamtoos and Algoa sub-basins, separated by fault-bounded basement arches composed of Ordovician to Devonian metasediments of the Cape Supergroup.

• Southern Outeniqua sub-basin is the distal extension of the northem sub-basins below the 300 m isobaths.

• Algoa sub-basin includes three half-grabens: onshore Sundays River Trough; on & offshore Uitenhage Trough; offshore Port Elizabeth Trough.

• Arcuate trend of the basin-bounding fault systems is most likely inherited from the structural grain of the underlying orogenic Cape Fold Belt (De Swardt & McLachlan, 1982).

• In Fig 1 the E edge of large fault systems coincides closely with the 200m isobath.

• Mesozoic sedimentary fill of the offshore South African rift basins is subdivided into synrift and drift phases of sedimentation.

Q4/R4


391



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



• The earliest synrift sediments are fluvial and lacustrine in origin, and in some areas are associated with volcanics and volcaniclastics. They are overlain in most basins by deltaic and shallow-marine sediments.

• The drift succession is characterised by deep-marine argillaceous sediments. In the Outeniqua basin the beginning of the drift phase is marked by the 14Atl mid-Albian unconformity.

• South Africa's western continental margin is a "passive" volcanic margin and encompasses the greater part of the Orange Basin sensu stricto, as well as a thin, elongate, sedimentary wedge along the the western flank of the Columbine-Agulhas basement arch.

Catuneanu et al. Reciprocal Flexural Behaviour and Contrasting Stratigraphies: A New Basin Development Model for the Karoo Retroarc Foreland System, South Africa

1998 Seismic Source

• Propose a basin development model for the Karoo Basin linked to paroxysms in the CFB.

• Authors envisage the palaeo-Pacific plate subducting underneath southern Gondwana, resulting in the Cape orogeny and sedimentation in the Karoo Basin

• Differ from previous authors by recognizing 8 paroxusms in the CFB. Hälbich (1983b) proposed our pulses of deformation for the CFB and Gresse et al. (1992) five episodic pulses of deformation of which three differ substantially from Hälbich. Catuneanu et al. (1998) considered these to be separate events and combined them (+ a 215 Ma event) to get to eight tectonic paroxysms. This is based on the recognition of stratigraphic patterns in the Karoo Basin rather than work in the CFB.

Q3/R1

Cornell et al. The Namaqua-Natal Province

2006 Seismic Source

• The N-N provinceof the NNMB refers to the igneous and metamorphic rocks formed or metamorphosed during the Namaqua Orogeny (1200-1000 Ma).

• Regional gravity and magnatic surveys, xenoliths from kimberlites and deep boreholes data supports existence of continuous belt 1400 km long and 400km wide. Its position relative to the Kaapvaal Craton is given in Fig.1.

• Overview tectonic model for the evolution of the Namaqua-Natal Province on pages 370 – 373, starting with the Kheisian events between 2000 – 1600 Ma.

Q4/R3

Dalziel et al. Plumes, Orogenesis, and Supercontinental Fragmentation

2000 Seismic Source

• Authors investigate the early Mesozoic Gondwanide fold belt, supporting the existence of this proposed mountain chain across South America, southern Africa, and Antarctica.

Q3/R4


392



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



De Beer, C.H. Simultaneous Folding in the Western and Southern Branches of the Cape Fold Belt

1990 Seismic Source

• The northwesterly and easterly trends of the Cape Fold Belt (CFB) meet in the southwestern Cape Syntaxis. Both trends form arcs of which the convex sides face east and northwest, respectively. The Syntaxis comprises a complex zone of NE-trending folds and faults stretching from Ceres to Cape Hangklip

• Northward directed compression of the southern CFB was deflected in the Syntaxis by the combined effect of a rigid (granitic) buttress (Stettyns Rise), a change in basement structural grain, and compression from the SW, to form the NE fold trend.

• The Malmesbury Group basement of the W domain was substantially stiffened by Cape Granite plutons. Consequently, a different deformational style might be expected in the cover rocks.

Q4/R4

De Beer, C.H. Structural Evolution of the Cape Fold Belt Syntaxis and Its Influence on Syntectonic Sedimentation in the SW Karoo Basin.

1992 Seismic Source

• The western branch of the CFB (WCFB) displays NW trending open folds without axial plane cleavage, and is transected by numerous faults with approximately the same trend. Megafolds swing progressively into a N-S orientation on approaching the Ceres syntaxis and ultimately become deflected to the SW

• In the E trending folds of the southern branch (SCFB), intense coaxial strains are indicated by the high incidence of second-order folds on megastructure limbs, northward overfolding and thrusting, as well as several cleavage generations.

• The syntaxis is dominated by NE-trending folds of the SCFB, with folds of the WCFB trending N-S.

• The syntaxis is transected at a large angle by the Worcester Fault, causing oblique sinistral displacement of fold axial traces in addition to a 5 km southerly down throw.

• Second-order folds trend NE on the northern limb of the Koo syncline. Further southeast, E-W folds seem to curve continuously into the NE trend of the syntaxis.

• Figures 1 & 2 show that there is a more gradual transition from NE orientated syntaxial folds to E-W southern branch structures.

• In Figure 2 second-order northeast-trending syntaxial folds are shown north of Montagu.

Q4/R4

De Beer, C.H. Fold Interference from Simultaneous Shortening in Different Directions: The

1995 Seismic Source

• The E-trending southern branch (or southern CFB) has a much higher deformational intensity, as indicated by the

Q4/R4


393



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Cape Fold Belt Syntaxis north-verging, recumbent 1st order folds, a high incidence

of 2nd

order folds and local out-of-the-forelimb thrusting. Both branches are cut by numerous post-tectonic normal faults

• The area of mergence between the western branch and southern branch folds is characterized by numerous NE-trending folds and was termed a syntaxis

• The syntaxis is transected at a large angle by the NW- to E-striking Worcester fault, causing oblique displacement of fold axial traces in addition to a primary 5 km southerly downthrow

• South of McGregor, second-order NE-trending folds occur on the limbs of larger E-trending folds.

De Beer, C.H. Structure of the Cape Fold Belt in the Ceres Arc

1998 Seismic Source

• CFB consists of an E-trending fold-thrust branch along the south coast and a less spectacular N-trending branch along the W coast. The two branches overlap in a syntaxis situated in the SW part of the Western Cape Province.

• Syntaxis is transcended at large angle by WNW striking Worcester fault which caused oblique sinistral displacement.

• Fig 1.1 shows that the change in fold trenc from NW to N in the western branch only occurs in the immediate vicinity of the syntaxis.

• NE trending folds dominate the core of the syntaxis. To the west and north it is replaced by N- and NNW-trending structures. To the east the NE folds merge with the E-trending folds of the Southern branch.

• While the role of buttresses or obstacles below the Palaeozoic cover is unknown, De Beer concedes that it could have been substantial.

Q5/R4

Used in determining W boundary

De Beer, C.H. The Stratigraphy, Lithology and Structure of the Table Mountain Group

2002 Seismic Source

• Figure demonstrates the two CFB branches.

Q3/R2

De Beer, C.H. Investigation into Evidence for Neotectonic Deformation Within Onland Neogene to Quaternary Deposits Between Alexander Bay and Port Elizabeth – South Coast Report

2005. Rupture Geometry

• Report a maximum displacement of 6km on the Worcester fault in the CFB syntaxis.

Q3/R3 Q3/R3

De Beer, C.H. Investigation into evidence for neotectonic deformation within onland Neogene to

2006 Seismic Source

• Confirmation that the position of the Kango fault agrees closely with the southern boundary of the Cape Isostatic

Q3/R2


394



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Quaternary Deposits Between Alexander Bay and Port Elizabeth – Executive Summary Report

Anomaly, approximately 50 to 60 km from the centre of this anomaly.

De Beer, C.H. Potential Onshore and Offshore Geological Hazards for the Bantamsklip Nuclear Site, South-Western Cape, South Africa: A Review of the Latest Airborne and Marine Geophysical Data and Their Impact on the Existing Geological model for the Site Vicinity Area

2007 Seismic Source

• Figure 3 shows the dominant syntaxial northeast trend for faults in the area immediately to the west of Cape Agulhas

Q3/R3

De Beer, J.H. The relationship Between the Deep Electrical Resistivity Structure and Tectonic Provinces in Southern Africa: Part 2

1978 Seismic Source

• N edge of the SCCB is also the edge of the NNMB.

• BMA coincides with the SCCB and propose that this is due to structures present in the Cape Basement.

Q3/R2

De Beer & Meyer

Geophysical Characteristics of the Namaqua-Natal Belt and Its Boundaries

1984 Seismic Source

• The NNMB envelops the SW, S and SE rims of the Kaapvaal Craton, and is in turn bounded by the Damara-Gariep-Malmesbury belts.

• N edge of the SCCB is probably the S boundary of the NNMB. The BMA anomaly coincides with this line and is described as an edge-anomaly.

Q3/R2

De Villiers et al. A Review of the Cape Orogeny

1944 Seismic Source

• The Cape system exhibits three main structural lines:

1. The Cedarberg foldings in the west, striking roughly N.N.W.-S.S.E.

2. The Cape foldings in the south with roughly E.-W strike.

3. The Lebombo monocline in the east (not relevant to this study).

• The Cedarberg foldings extend south-south-eastwards from near Van Rhynsdorp with syn- and anticlines that are open in the north, but becoming more closed towards the south.

• At right angles to this belt there is the southern Cape fold-belt, or Zwartberg foldings, also referred to in a somewhat wider sense, by Du Toit as the Gondwanide orogenic belt. They stretch in a gently curved belt at least 100 miles wide from Worcester in the west to the mouth of the Fish River in the east. In the southern belt the folding is more intense, but decrease towards the east of the southern

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belt.

• These two tectonic lines met in a region of syntaxis in the Worcester-Ceres area

De Wit & Ransome

Regional Inversion Tectonics Along the Southern Margin of Gondwana.

1992 Seismic Source

• It has been reasonably well established that two first-order episodes of both compression and extension have alternated along the southern margins of Gondwana over a period of circa 600 Ma since the late Precambrian.

1. Pan-Gondwanean convergence circa 650 ± 100 Ma,

2. late-Proterozoic to early Paleozoic extension circa 500 ± 100 Ma,

3. late Paleozoic convergence circa 300 ± 100 Ma and

4. mid- to late Mesozoic extension circa 150 ± 50 Ma.

• Episodes of convergence are both believed to be related to the formation/consolidation of supercontinents. Episode (i) is associated with the fusion of greater proto-Gondwana; Episode (iii) is related to the assembly of Pangea. The “Pan-African/Braziliano” and “Hercynian” age fold belts are the major manifestations of these two episodes, respectively

• Extension during episode (ii) relates to the break-up of greater proto-Gondwana, which resulted, inter alia, in the formation of an extensive “passive” rift margin along the southern edge of Gondwana.

• Extension during episode (iv) relates to the break-up of Pangea and Gondwana, with the subsequent opening of the southern oceans.

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Doherty The Seismic Expression of the St. Croix Fault Plane, Offshore Algoa Basin, Showing a History of Extension, Inversion, Compression, and Strike-Slip


• The St Croix fault appears to be a thrust fault, reactivated as a normal fault and later cut by strike-slip faults.

• The mechanism for the folding of the St Croix fault is believed to be left lateral motion along the Uitenhage Fault – a dip-slip fault with a strike-slip component of about 5 km, which formed at the end of rifting.

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Durrheim Seismic Reflection and Refraction Studies of the Deep Structure of the Agulhas Bank

1987 Seismic Source

• In the author’s Figure 2, the position of the Moho (M) is shown at a depth of 30 km.

Rupture style

• Based on an unpublished study (Harper, 1977), virtually all the faults are considered to be steeply dipping normal faults.

Rupture Geometry

• Near the coastline and most distant from the Agulhas Fracture Zone the dominant fault strike is 87° (parallel to

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CFB structural grain). Within 100 km of the AFZ the predominant fault strike is 132° and twice as many faults dip to the southwest as to the northeast. This overlay of extensional block faulting on the simple wrench pattern is indicative of divergent wrenching

Du Toit Our Wandering Continents: An Hypothesis of Continental Drifting

1937 Seismic Source

• Propose that the CFB is part of a larger mountain stretching across Gondwana.

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Eglington Evolution of the Namaqua-Natal Belt, Southern Africa – A Geochronological and Isotope Geochemical Review

2006 Seismic Source

• The fabric-forming event (1.07 Ga) appears to predate the geochronological record of high-temperature metamorphism (1.03 Ga) in the Mzumbe terrane. Similarly in Bushmanland, the regional penetrative fabric predates intrusion of the Spektakel Suite (1.03–1.06 Ga) but peak metamorphism occurred at 1.03 Ga.

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Eglington, B.M.& Armstrong

Geochronological and Isotopic Constraints on the Mesoproterozoic Namaqua-Natal Belt: Evidence from Deep Borehole Intersections in South Africa

2003 Seismic Source

• Mesoproterozoic lithologies of the Namaqua–Natal Belt are exposed in the west and east of South Africa but the central section of the belt is obscured by younger sedimentary cover. This belt is one of several Grenvillian-aged belts world-wide and is of importance in reconstructions of the Meso- to Neo-Proterozoic supercontinent of Rodinia

• Dates for emplacement and extrusion of the various magmatic components of the different sub-provinces and terranes of the NNMB are summarized in comprising the Namaqua–Natal Belt are illustrated in Fig. 4. Four main periods of activity are evident: at ∼1.8 to 2 Ga, ∼1.2 Ga, ∼1.15 Ga and ∼1.06 Ga.

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Eglington et al. Geological, Geophysical and Isotopic Constraints on the Nature of the Mesoproterozoic Namaqua-Natal Belt of Southern Africa

1993 Seismic Source

• Southern limit of the NNMB may be delineated by Beattie anomaly and associated Southern Cape Conductive Belt.

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Eglington et al. Isotope and Geochemical Constraints on Proterozoic Crustal Evolution in Southeastern Africa

1989 Seismic Source

• Authors proposed a 3-stage model for the development of the NNMB between 1.5–0.9 Ga.

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Fairhead Mesozoic Plate Tectonic Reconstructions of the Central South Atlantic Ocean: The Role of the West and Central African Rift Systems

1988 Seismic Source

• Propose a four-stage development of the opening of the Atlantic basins:

1. Stage 1, Jurassic opening of the Central Atlantic

2. Stage 2, the Early Cretaceous opening of the South Atlantic

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3. Stage 3, the opening of the Equatorial Atlantic

4. Stage 4, the linkage of these oceanic basins and development of a single opening mid-oceanic rift system

Goedhart A Geological Investigation of Neotectonic Reactivation Along the Ceres-Kango-Baviaanskloof-Coega Fault System in the Southern and Eastern Cape, South Africa: Desk Study Report

2004 Seismic Source

• In the Eastern Cape, the NE-SW trending joints and secondary faults are commonly steeply dipping, with offsets measurable in metres, sometimes forming horst blocks.

Rupture Orientation & Style of Faulting

• Right-lateral movement along some of these transfer faults offset the northern and eastern margins of the Algoa basin southward. Both the major normal faults, and high-angle strike-slip faults, are necessary to allow for discontinuous slip and listric rotation of the main basinal elements and may account for the block-like fragmentation of the northeastern onshore margin of the Algoa basin.

• A similar low dip angle is reported for the Coega Fault west of Uitenhage (Ingram, 1994), but it steepens up to about 70° near the Coega River mouth, where southward displacement is approximately 2km. It extends offshore into the Algoa Bay as the St. Croix Fault, which curves southward towards the Agulhas Fracture Zone along the continental margin (Doherty, 1992; Fouché et al., 1992; Ben Avraham, 1995).

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Goedhart A Geological Investigation of Neotectonic Reactivation Along the Ceres-Kango-Baviaanskloof-Coega Fault System in Southern and Eastern Cape, South Africa: Field Reconnaissance Report


• Scarp morphology across the region suggests surface rupture by dominantly dip-slip normal faulting, although strike-slip is reported from a NNE-SSW striking left-lateral transfer fault near the Witkop site.

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Goedhart A Geological Investigation of Neotectonic Reactivation Along the Ceres-Kango-Baviaanskloof-Coega Fault System in the Southern and Eastern Cape, South Africa: Trench Report


• Although possibility of some strike-slip component is acknowledged (p. 9), only evidence for normal slip was reported in this report.

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Goedhart Potential Onshore and Offshore Geological Hazards for the Thyspunt Nuclear Site, Eastern Cape, South Africa: A Review of the Latest Airborne And Marine

2007 Rupture Orientation & Style

• Vertical fault movement along W-E faults may, in places, result in a sharp offset along the strike of dipping fold limbs, which, if observed in isolation, may appear to reflect left-lateral or right-lateral faulting. An example of

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Geophysical Data and Their Impact on the Existing Geological Model for the Site Vicinity Area

this is the NE-SW striking family of Paul Sauer transfer faults which appears on the CGS 1:250 000 scale map in the Kareedouw – Cambria area, just NW of the 40km Site Vicinity radius. This NE-SW fabric is pervasive throughout the region, and in the Thyspunt Site Vicinity and Site Areas.

Goedhart et al. Groundwater Targeting in the Algoa Bay Region, from Humansdorp to Alexandria, Eastern Cape, South Africa

2004 Seismic Source

• At the Coega River mouth, the Coega Fault offsets the Palaeozoic basement by over 1800m.

• In Fig. D5.7 the total displacement at the river mouth (where fault zone is ~1km wide) is estimated at 2km

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Gough et al. A Magnetometer Array Study in Southern Africa

1973 Seismic Source

• Report the discovery of a major conductive structure under the Cape Folded Belt and southernmost Karroo

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Gresse Lithostratigraphy and Structure of the Kaaimans Group

1983 Seismic Source

• Recognised three deformation phases in the Kaaimans Group near George and Knysna: The first two is of Silurian age (i.e. they pre-date the CFB orogeny), while the third is correlated with the CFB.

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Gresse et al. Tectonic Inversion and Radiometric Resetting of the Basement in the Cape Fold Belt

1992 Seismic Source

• Four whole-rock samples from the Malmesbury Group between Worcester and Robertson, one from Riebeek Kasteel in the Swartland terrane and one from the Witteberg Group were analysed

40Ar/

39Ar stepheating

• 40

Ar/39

Ar age spectra peak at 223Ma, 239Ma, 259Ma, 276Ma and 294Ma, reflecting episodic pulses of deformation in the fold and thrust belt.

• Halbich’s 215Ma event probably records late diastrophic uplift of the Cape orogen or mantle doming prior to continental breakup

• During a subsequent negative inversion event Permo-Triassic thrusts were reactivated in a reverse sense as normal faults that follow major fold structures of the SCFB, have southerly displacements of up to 6km and are up to 300km long. Newark-type half-grabens filled with Jurassic-Cretaceous sediments of the Uitenhage Group formed along the southern downthrown sides of these faults

• All these east-west striking exposures within the Cape Fold Belt are transected along their long axes by large strike faults of Mesozoic age such as the Worcester and Kango faults.

• Pan-African aged (Saldanian) rocks underlying the Palaeozoic, Cape Supergroup in the Cape Fold Belt were

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positively inverted during the Permo-Triassic Cape Orogeny and negatively inverted during the subsequent breakup of Gondwana in Jurassic-Cretaceous times.

Gresse et al. Namibian (Neoproterozoic) to Early Cambrian Successions

2006 Seismic Source

• The Kaaimans Group is exposed in an unroofed mega-anticline of the Permo-Triassic CFB in the George-Knysna area south of the Outeniqua Range

• The Cango Caves and Kansa Groups form an inlier in a mega-anticline of the Swartberg Range north of Oudtshoorn that are separated by an unconformity. The Cango Caves Group was folded prior to the deposition of the Kansa Group.

• The Gamtoos Group is exposed in a mega-anticline of the CFB in the PE region. The northern contact is marked by the Elandsberg Fault and to the South the boundary is formed by the Gamtoos fault. The Gamtoos Group, like the Kaaimans and Cango Caves Groups, suffered successive coaxial deformation events related to both the Saldanian and Cape orogenies.

•

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Gurniss et al. Constraining Mantle Density Structure Using Geological Evidence of Surface Uplift Rates: The Case of the African Superplume

2000 Seismic Source

• These authors estimated Pliocene uplift of 30 – 80 m, which is much lower than uplift of 900 m proposed by Partridge & Maud (1987).

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Hälbich A Geodynamic Model for the Cape Fold Belt

1983a Seismic Source

• Propose an orogenic model based on a short-lived, small convection cell or plume, that is estimated to have lasted only 50 Ma.

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Hälbich A Tectonogenesis of the Cape Fold Belt

1983b Seismic Source

• The tectonic history of the CFB is outlined with the aid of four dated consecutive paroxysms, between the Permian into the middle Triassic.

• The first deformation leading to a paroxysm in the CFB is dated at 278 ± 2 Ma ago (i.e. earliest Permian). The first surge produced the Kango Anticlinorium and the proto-Swartberg by an average horizontal shortening of 35%.

• The second collapse of cover rocks came around 258 ± 2 Ma in the early Middle Permian, when the George Anticlinorium developed with some 70 per cent of horizontal shortening in his zone 6.

• The third event is dated at ~246 Ma.

• The foutyh event is dated at 230 ± 3 Ma.

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Hälbich Disharmonic Folding, Detachment and Thrusting in the Cape Fold Belt

1983c Seismic Source

• Thrust phenomena and fold intensities increase eastward towards the Baviaanskloof Mountains up to 24°E.

Fault Geometry

• Normal faults dip to the south.

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Hälbich The Cape Fold Belt Orogeny: State of the Art 1970s – 1980s

1992 Seismic Source

• Author mentions that on a regional scale thrust phenomena become more frequent east of Meirings Poort towards Snykloof, Toverwater Poort and the Baviaanskloof Range. Fold intensities also increase up to longitude 24° east.

Rupture Geometry

• Author reports that thrusts in the Meirings Poort profile dips South (see Fig 10.10 for thrust dips in the Baviaanskloof Range).

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Hälbich et al. Dating the Cape Orogeny 1983 Seismic Source

• This paper report on the results of 40

Ar/39

Ar step heating analysis on selected fine-grained rocks from the southern Cape Fold Belt. This is repeatedly confirmed from various parts of the belt and interpreted as successive deformations producing distinct co-zonal cleavages

• An episodic geological history, with the following individual climaxes are proposed: 278 , 258 , 248 , 230 and 215 Ma respectively.

• This youngest assemblage (215 ± 5 Ma) is proposed to mark a late (final?) diastrophic uplift of the Cape orogen that produced the mountain chain source area for the Molteno Formation, or to be related to the beginning of mantle doming prior to continental disruption, leadoing to Karoo magmatic activity starting with alkaline intrusive complexes and minor intrusions around 204 ± 5 and lava outpourings around 193 ± 5 Ma. However this last event is excluded from the proposed paroxysms in Hälbich (1983b)

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Hälbich & Swart Structural Zoning and Dynamic History of the Cover Rocks of the Cape Fold Belt

1983 Seismic Source

• Identify differences in the amount of deformation experienced by different areas in the Karoo and Cape supergroups. The southernmost part of the Karoo Supergroup experienced limited deformation, with the more most intense deformation exhibited by the rocks of the Cape Supergroup.

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Hales & Gough Isostatic Anomalies and 1960 Seismic Source Q3/R2


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Crustal Structure in the Southern Cape

• This paper reports on a negative isostatic anomaly in the Southern Cape in the region between the escarpment and the sea, approximately 200 km from the south and east coasts

• The authors consider that these negative anomalies to arise from the compensation of at least 1.6 km topography which has been removed by erosion over an 80 km wide belt.

• They proposed that the maximum stress is situated between 50 and 60 km from the centre line and that failure will occur at these points. They also compare this line with the fault system that at this point 22° E.

Hanson et al. Thyspunt Geological Investigations—Kango Fault Study


• Only vertical slip is reported in this investigation.

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Harvey et al. Structural Variations of the Crust in the Southwestern Cape, Deducted from Seismic Receiver Functions

2001 Seismic Source

• Receiver functions were generated from seismic traces recorded by seismographs in the southwestern Cape to estimate the crustal thickness and other crustal features.

• The Moho is found at variable depths. Over a distance of some 300km, from Kenhard southward, the Moho increases from about 45km to ~ 50km. Beneath the northern margin of the SCCB and the Beattie Anomaly, the Moho starts to dip to the north. Southward, for 150km beneath the frontal sector of the eastern branch of the Cape Fold Belt (north of the Kango Fault), the crust thins to less than 40km. Farther southward still, for ~50km beneath the central sector of the eastern branch of the Cape Fold Belt to the (extension of) the Worcester Fault, the crust thickens again to about 45km. South of the Worcester fault the crust thins again to less than 30km at the coast. The general thinning of the Moho beneath the Cape Fold Belt is counter-intuitive. This suggests that major extensional faults or décollements zones, associated with the regional Jurassic-Cretaceous extension, are rooted in the underlying crust, perhaps focussed along the south dipping contacts of the SCCB

• The source of the Beattie Anomaly becomes subdued west of stations SA07 and SA04, and disappears as it approaches the north-south trending Western Branch of the Cape Fold Belt (Figure 1). In contrast, the SCCB continues as far as the Atlantic coast (Figure 1), without being significantly affected by the north-south trending deformational fabrics of the Paleozoic and Saldanian structures. This suggest that the Mesoproterozoic basement of the Namaqua Natal Mobile Belt continues below the Western branch of the Cape Fold Belt. The western limit of the Beattie Anomaly may therefore be a

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result of tectono-sedimentary burial by relatively shallow Saldanian- and Cape Basin-age sequences.

• Thus, like the similar trending Beattie anomaly, a crustal source for the conductive rocks is clear. De Beer and Gough (1980) and de Beer et al. (1974; 1982; 1992) interpreted this source to be an elongated body of relatively dense and electrically conductive crust, possibly a partially serpentinised slice of paleo-oceanic lithosphere which they suggested marked the southern edge of the Namaqua-Natal Mobile Belt.

Jackson Active Normal Faulting and Crustal Extension

1987 Seismic Source

• Propose that the formation of many continental sedimentary basins and passive margins involved a considerable amount of both lithospheric and crustal stretching. He postualtes that stretching continues beyond ß = 1.7 have three possibilities:

1. A second generation of steep faults becomes active, cutting the first generation faults, which have rotated to a dip of 30°, making them inactive.

2. The faults continue to move at dips of less than 30° but do so aseismically.

3. The faults become inactive once their dips reach 30°, and extension, with new faults, continues somewhere else nearby.

• Where values for stretching factors exceeding ß = 1.7 have been suggested on land, two generations of normal faults have usually been described.

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Johnson et al. Sedimentary Rocks of the Karoo Supergroup

2006 Seismic Source

• Authors support the proposed retro-arc foreland basin model for the Karoo Basin that formed as a result of northwards subduction of oceanic lithosphere located south of the arc.

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Kingsley A Composite Submarine Fan-Delta-Fluvial Model for the Ecca and Lower Beaufort Groups of Permian Age in the Eastern Cape Province

1981 Seismic Source

• Author propose that continent-continent collision south of the Karoo Basin; created the Karoo Basin and CFB

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Le Roux The Lithostratigraphy of Cenozoic Deposits Along the South-East Cape Coast as Related to Sea-Level Change

1989 Seismic Source

• This thesis provides a thorough description, stratigraphic classification and depositional interpretation of the marine, aeolian deposits of the Algoa Group

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Le Roux Structural Evolution of the Kango Group

1983 Seismic Source

• Author recognises 4 phase of deformation of the Kango Group, of which the 1

st two predates the CFB orogeny,


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the 3rd

is correlated with the CFB and the 4th to the

Mesozoic inversion and continental break-up.

Lindeque et al. Deep Crustal Profile Across the southern Karoo Basin and Beattie Magnetic Anomaly, South Africa: An Integrated Interpretation with Tectonic Implications

2011 Seismic Source

• Authors present a detailed deep crustal model constructed from the joint interpretation of:

1. archive data comprising surface geology, aeromagnetic data, nearby deep boreholes, teleseismic receiver functions and regional seismic reflection profiles, and

2. line coincident newly acquired high-resolution geophysical data consisting of near vertical seismic reflection data, shallow P- and S-wave velocity data, wide-angle refraction data, high resolution magnetotelluric data and impedance spectroscopy measurements on borehole samples.

• The Karoo Supergroup, disrupted by low-angle thrust faults rooted in a zone of local décollements in the lower Ecca Group, rest paraconformably on a continuous undeformed sub-horizontal ~1.5 to 10 km thick wedge of the Cape Supergroup (CSG).

• The Cape Supergroup forms a continuous undeformed sub-horizontal wedge, 10 km thick at the CFB front in the south and 1.5 km thick under the escarpment in the north. It continues below the escarpment and does not pinch out as previous geological-based models suggest. However, the Witteberg Group still pinches out further south before borehole SA-1/66.

• A series of low angle listric thrusts/faults are identified in the upper crust (Cape Supergroup & Karoo Supergroup). Listric faults form an important component of the authors’ model.

• The northernmost limit of combined low angle thrusting and significant folding of the Cape Supergroup is restricted to the Cape Fold Belt front. The low angle faults do not appear to penetrate the basement as the Hälbich (1993) model implied (compare Figures 10a and 10d).

• Data do not support earlier models whereby the southernmost boundary of the NNMB was defined by a deep BMA and the Southern Cape Conductive Belt, possibly abutting a Pan African (Neoproterozoic) suture zone beneath the Cape Supergroup. NNMB continues beneath the CFB and possibly farther south below the CFB up to AFFZ

• The postulated Pan African suture zone at the BMA does not exist. Instead, Pan African aged (520 to 650 Ma) outcrops are limited to the Gariep, Saldanian and the aligned Agulhas-Columbine Arch units on the West coast

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(Figure 11). On the South coast, the granite outcrops at George (latitude 34°S, longitude 22.5°E) might imply a Saldanian suture farther south, but not at the CFB front as the previous models assumed

• Crustal model reveals that the BMA is neither a southern boundary of the NNMB, nor a major Pan African suture, and calls for a significant adjustment of the crustal model of southern Africa

• BMA and SCCB may be geophysical manifestations of tectonically(?) disrupted stratabound ore deposits that may have been further remobilised through metasomatic processess of late stage hydrothermal fluids during NNMB orogenesis. This theory is speculative and need to be tested by deep drilling.

• They propose a model for the CFB-Karoo basin as a wide, upper crustal thin skinned Jura-type fold belt, formed in response to continent-continent collision, or suturing south of the CFB, with subduction to the south. This seems perfectly feasible in a larger Gondwana framework (Milani and de Wit, 2008) and as was also suggested for the Sierra de la Ventana in Argentina (Ramos 1988, 2008

Rupture Geometry

• Figure 9 shows south-dipping thrusts in the sub-surface Cape Supergroup.

Lock Flat-Plate Subduction and the Cape Fold Belt of South Africa.

1980 Seismic Source

• A flat-plate subduction model is proposed for southwestern Gondwanaland to explain the Cape Fold Belt of South Africa. They estimate that the fold belt is located at distances of as much as I ,000 km from the continental margin of the time, and it is suggested that the descending slab of oceanic lithosphere is subducted along the Andean margin of the continent became coupled with part of the overriding continental crust of Gondwanaland.

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Malan et al. The Structural And Stratigraphic Development of the Gamtoos and Algoa Basins, Offshore South Africa

1990 Fault geometry

• Report displacement of 12 km on the Gamtoos fault.

• Three models proposed to explain the S-wards curvature of major faults.

4. Bending as result of pull-apart

5. Bending as result of dextural deformation

6. Inherited from Cape Fold Belt structures

• Early Cretaceous tensional stresses rejuvenated dip-slip and minor strike-slip movement along the large arcuate

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basin-bounding faults resulting in limited downfaulting of the synrift (hanging wall) sequence. Dip-slip and limited strike-slip movement of the hanging wall sequence along the curved Gamtoos Fault. Along the northwest-southeast trending section of the Gamtoos Fault, simple dip-slip movement combined with a small degree of rotation produced extensional faulting synthetic to the basin bounding fault.

Martin & Hartnady

Plate Tectonic Development of the Southwest Indian Ocean: A Revised Reconstruction of East Antarctica and Africa

1986 Seismic Source

• Show a sequence of reconstructions for East Antarctica relative to Africa that show the Falkland Plateau to have cleared the African continent by late Cretaceous.

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Martini On the Presence of Ash Beds and Volcanic Fragments in the Graywackes of the Karroo System in the Southern Cape Province (South Africa)

1974 Seismic Source

• Envisage the Patagonia Massif to form part of the Gondwana continent with oceanic crust subducting from the west underneath the continent. As a result the Permian (Gondwanide?) mountain range, geologically similar to the Andes mountains, is formed in southern Gondwana.

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McMillan et al. Late Mesozoic Basins off the South Coast of South Africa

1997 Seismic Source

• In the Pletmos Basin the pre-Mesozoic basement has been penetrated on basement highs only and consists mainly of Ordovician-Silurian Table Mountain Group quartzites belonging to the Palaeozoic Cape Supergroup.

• In the Gamtoos & Algoa Basins the arches separating basins are composed mostly of the Palaeozoic Cape Supergroup (mainly Ordovician-Silurian Table Mountain quartzites and Devonian Bokkeveld slates) which are aligned along the grain of the Permo-Triassic Cape Fold Belt. Deep drilling offshore has intersected basement rocks (Table Mountain quartzites) only on the flanks of the basement arches and on basement highs.

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Milani & De Wit Correlations Between the Classic Paraná and Cape–Karoo Sequences of South America and Southern Africa and Their Basin Infills Flanking the Gondwanides: Du Toit Revisited

2008 Seismic Source

• Paper looking at the histories of the Paraná and Cape–Karoo basins that evolved together along a common early Palaeozoic Gondwana margin facing the Panthalassa. This margin was transformed into a series of linked foreland basins coupled to the evolution of the Gondwanides.

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Newton The Cape Folding – A Syntaxis or Not?

1993 Seismic Source

• The origin and use of the word 'syntaxis' are briefly reviewed and it is concluded that it is only appropriate to the geometry of the pre-Cape (Saldanian) structures.

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Newton et al. The Cape Fold Belt 2006 Seismic Source Q3/R3


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• The Late Permian to Early Triassic orogeny affected the sandstones and shales of the Cape Supergroup, but also the older pre-Cape rocks and younger Karoo Supergroup strata, although only the southernmost part of the Karoo Basin

• The Cape Fold Belt is characterised by a series of northwest- to north-trending folds in the west, stretching from Stellenbosch in the south to Vanrhynsdorp in the north, and by folds striking approximately east-west in the central and eastern areas, from Swellendam in the west to the Great Fish River mouth in the east. The two arms of the fold belt meet in the syntaxis" (or "virgation" - see Newton, 1993a), a domain characterised by complex faulting and folding.

• They recognised that the Cape Fold Belt has for long been considered to form part of a much more extensive Gondwanide fold belt, although they acknowledge that there are problems on how the various elements need to be fitted together to form a continuous Gondwanide fold belt. They conclude by saying that the CFB is still poorly understood and inadequately studied.

Nguuri et al. Crustal Structure Beneath Southern Africa and Its Implications for the Formation and Evolution of the Kaapvaal and Zimbabwe Cratons

2001 Seismic Source

• While results are comparatively sparse for the Namaqua-Natal and Cape Fold belts, measurements of crustal thickness are typically 40-50 km throughout the Namaqua-Natal belt and northern Cape Fold belt. Within the Cape Fold belt, the crust thins to about 30 km near the African coast. Also see Figure 3.

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Parsiegla et al. Deep Crustal Structure of the Sheared South African Continental Margin: First Results of the Agulhas-Karoo Geoscience Transect

2007 Seismic Source

• Based on the western of two combined offshore-onshore seismic reflection/refraction profiles.

• Southwards thinning of the crust (see Figures 7 & 10). The observed crustal thickness (including sediments) along the profile varies from 30 km on the inner continental shelf to 7 km in the Agulhas Passage.

• On the Agulhas Bank, the crustal thickness ranges between 26 and 30 km (Figure 7). The thickness of the crust underlying the Southern Outeniqua Basin declines from 25 km in the north to 22 km in the south. Beneath the Diaz Marginal Ridge, the crust thins from 22 km to 19 km.

• The transition zone from continental to oceanic crust is 52 km wide (profile distance 478 to 530 km); a typical value for sheared margins (Bird, 2001). It is characterised by a sharp decrease in crustal thickness from 30 km on the continental side to 7 km on the oceanic side and by a southeastward increase in average crustal P-wave

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velocity

Parsiegla et al. The Agulhas Plateau: Structure and Evolution of a Large Igneous Province

2008 Seismic Source

• The velocity–depth structure of the Agulhas Plateau is typical for overthickened oceanic crust observed at oceanic Large Igneous Provinces.

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Parsiegla et al. Southern African Continental Margin: Dynamic Processes of a Transform Margin

2009 Seismic Source

• The authors use 3 types of geophysical data sets collected along two combined seismic land-sea profiles to investigate the deep crustal structure of a transform margin and to characterize processes active at these margins by studying the Agulhas-Falkland Fracture Zone, the Outeniqua Basin, and the Diaz Marginal Ridge.

• Similarities in average (crystalline) crustal velocities for the stretched onshore and offshore continental crust suggest that rocks of the Cape Supergroup underlie the shelf area (beneath the Outeniqua Basin and Diaz Marginal Ridge), consistent with drilling data. Uppermost crustal velocities of between 4.5 and 5.5 km/s (Figure 6b) fit well in the velocity range of the lithologically diverse Cape Supergroup mostly consisting of sedimentary and metamorphically overprinted sedimentary rocks.

• According to the velocity-depth structure and the average velocities of the crystalline crust (Figures 6a and 6b), the profile can be subdivided into four units from north to south

5. From 0 to 300 km profile distance, the crust is about 42 km thick on the onshore part and about 28 km on the shelf. These thicknesses are within the normal ranges for unstretched and stretched continental crust [e.g., Christensen and Mooney, 1995]. The onset of crustal thinning begins 50 km inland from the coast.

6. The region between 300 and 350 km profile distance (Figure 6b) is characterized by the Moho’s ascent from 25 to 14 km over a distance of 50 km,

7. The crustal thickness in the Agulhas Passage varies between 6 and 10 km (350 to 435 km profile distance). Although this thickness is in the normal range for oceanic crust, the average crustal velocity of 6.04 km/s is at the lower limit of those reported

8. On the Agulhas Plateau (profile distance 435–890 km), the crustal thickness increases again to an average of 20 km. This significantly higher average crustal velocity (6.5 km/s) is due to the Agulhas Plateau’s ~10 km thick high-velocity lower crustal body, which identifies it as a Large Igneous Province [Parsiegla et al., 2008].

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• See section on Calculation of Crustal Stretching Factors: Thinning of continental crust between distances 180 and 520 km on the western profile is considered to be the result of crustal stretching (Figure 6c). A significantly smaller part of the eastern profile consists of stretched continental crust (Figures 6a and 6b, 150–340 km profile distance).

• Stretching factors increase from north to south along both profiles (Figure 8). The lowest stretching factors were observed in the southernmost CFB with average ß factors of 1.1–1.2. Peak ß factors occur next to the AFFZ (ß = 3.2–3.3). Stretching factors in the Pletmos and Gamtoos Basins are similar (ß = 1.6), while even higher in the Southern Outeniqua Basin ß = 1.9.

• Also see Figure 8 where average stretch factors are shown and Outeniqua Basin is subdivided into an area which experienced one; and a second, more southerly area which was affected by two stretching episodes (separated by a dashed line).

• Calculated Outeniqua Basin stretching factors can be interpreted as reflecting one episode of extension in the northern subbasins and two episodes in the wider southern basin.

• The shear motion along the Agulhas Falkland Transform started ~136 Ma and actively forms the continental margin and caused a second pulse of crustal stretching in the Outeniqua Basin (see Figure 9).

Rupture Geometry


Partridge & Maud

Geomorphic Evolution of southern Africa Since the Mesozoic

1987 Seismic Source

• Landmark paper where the authors propose that the Cenozoic evolution of southern Africa subcontinent occurred through extensive, episodic uplift (especially during the Miocene and Pliocene) with extended intervening periods of stasis.

• By late Aptian and early Albian times movements along the coastal margin had virtually ceased, and widespread epeirogenic sedimentation over the slowly subsiding continental shelf.

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Paton Influence of Crustal Heterogeneity on Normal

2006 Seismic Source

• This study investigates the development of the southern

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Fault Dimensions and Evolution: Southern South Africa Extensional System

South African extensional system.

• The Late Paleozoic Cape Orogeny generated the Cape Fold Belt, which deformed the Cape Supergroup in a series of E–W-trending and S-dipping thrusts, and dominates the structural configuration of southern South Africa. Author recognises a correlation in the trends of the Cape Fold Belt structural fabric and the Mesozoic extensional faults, and this is especially evident to the southeast where there is change in trend from an E–W orientation to a NW–SE trend of both the structural fabric and the extensional faults

• Overall displacement–length dimensions of the extensional faults were inherited from the underlying compressional faults

• Kango, Baviaanskloof and Gamtoos arrays are considered part of the same fault system that is at least 480 km long. The fault system, and the arrays that comprise it, are therefore comparable with the longest fault systems that have been documented in continental lithosphere

• This 480 km-long Mesozoic extensional system comprises a number of fault arrays that vary in length from 78 to 230 km. Coupled with displacements of up to 16 km, the fault arrays are amongst the longest and largest displacement of high angle normal faults (dips of 45–60°) documented in continental lithosphere.

Rupture Geometry & Style of Faulting

• Towards the SE the extensional faults change in trend from an E–W orientation to a NW–SE trend of both the structural fabric and the extensional fault.

• Displacement in the offshore Pletmos and Gamtoos basins are consistently larger than 12 km. The displacements of the hanging-wall to footwall cut-offs are estimated to be 13,000 m and 16,500 m respectively (conservative estimates).

• The Kango and Baviaanskloof Fault planes are visible at some localities and dip at approximately 60° towards the south.

Paton et al. Applicability of Thin or Thick Skinned Structural Models in a Region of Multiple Inversion Episodes: Southern South Africa

2006 Seismic Source

• The deformation of the Cape Fold Belt has been attributed to repeated structural reactivation of a mega-detachment from the late Proterozoic to the Mesozoic (650±65 Ma).

• Their regional scale cross-sections through the Permian-Triassic Cape Fold Belt reveal that it comprises two main structural domains:

3. A northern domain dominated by the low-relief Karoo

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foreland basin displaying northward verging and asymmetric folds

4. A southern domain that comprises of Cape Supergroup rocks that displays a series of approximately 8 km wavelength box folds and is responsible for the high topography of the southern Cape with elevations of up to 1500 m.

Paton & Underhill

Role of Crustal Anisotropy in Modifying the Structural and Sedimentological Evolution of Extensional Basins: The Gamtoos Basin, South Africa

2004 Seismic Source

• The authors investigate the structural and sedimentological evolution of the Mesozoic Gamtoos Basin, using 4700 km of sub-surface data (2D seismic and boreholes) from the offshore portion of the Gamtoos Basin.

• The Gamtoos Fault has A 90° bend in the Gamtoos Fault trace that we propose is caused by underlying structure.

• In contrast, the rapid establishment of length in the Gamtoos Fault and the localisation of displacement onto the basin-bounding fault resulted in the rapid transition from a terrestrial environment in the very earliest syn-rift episode (below seismic resolution) to a deep water, anoxic setting within ~5 My of rift initiation.

Style of Faulting

• The Gamtoos basin is inferred to have been undergoing a dominantly WSW-ENE extension orientation. There is no evidence of deformation (oblique folding or faulting) associated with strike-slip motion along either portion of the fault.

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Pitts et al. Interpretation of Magnetic, Gravity and Magnetotelluric Data Across The Cape Fold Belt and Karoo Basin

19925 Seismic Source

• Magnetic, gravity and magnetotelluric data from north -south profiles in the southern Cape Province of South Africa are used to interpret the crustal structure beneath the Palaeozoic Cape Supergroup and upper Palaeozoic, Mesozoic Karoo Sequence sediments.

• Based on magnetic data the Beattie magnetic anomaly is modelled as a 30 km wide body, located 7 km below surface and dipping to the south.

• There is a close correlation between the northern edge of the Southern Cape Conductive Belt (SCCB) and the Beattie magnetic anomaly. Based on magnetotelluric resistivity-depth models a zone of electrically conductive crust have been identified that correlates spatially with the body modelled as the source of the Beattie magnetic anomaly.

• Propose the same model for the origin of the Beattie

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anomaly and position of the southern edge of the Namaqua belt.

• The origin of these features is still enigmatic but it is possible that the cause is serpentinised oceanic lithospheric material, but they may also be as a result of mineralised low angle thrust faults.

• The gravity modelling shows that the continental crust south of the escarpment is overcompensated and that the crust is composed of zones of marginal gradational density.

Quesnel et al. Simple Models for the Beattie Magnetic Anomaly in South Africa

2009 Seismic Source

• Magnetic data used to develop models which predict the 1 km-altitude aeromagnetic measurements along a profile across the BMA and compare their results with the interpretation of independent magnetotelluric and seismic experiments along the same profile. Geological sources for the BMA are suggested to be located in the middle crust and may be displaced by a shear zone or a fault. Contrary to previous models suggesting a serpentinized sliver of paleo-oceanic crust within the Natal–Namaqua Mobile Belt, they propose that granulite-facies mid-crustal rocks within this belt may cause the BMA.

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Ramos Discussion on ‘Tectonostratigraphy as Applied to Analysis of South African Phanerozoic Basins’

1986 Seismic Source

• Supports the continent-continent collision model of Winter (1984) to explain the origin of the CFB.

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Ransome & De Wit

Preliminary Investigations into a Microplate Model for the South Western Cape.

1992 Seismic Source

• In this paper the authors speculate that the structural features observed within the syntaxis can be accounted for by the interaction of microplates, formed during the Late Precambrian intrusion of granite suites.

• Two main structural trends are recognised in the southwestern Cape: a N-striking Western Branch of the Cape Fold Belt, and an E-W-striking Southern Branch. The two branches coalesce to produce a NE-striking syntaxis. They consequently recognises three structural domains within the southwestern Cape:

1. Western Branch of the Cape Fold Belt,

2. Southern Branch,

3. An intervening Syntaxis Domain.

• The Western Branch and Syntaxis Domain of the Cape Fold Belt can both be further subdivided into two subdomains. For the position of the syntaxis domains see Figure 1 and Figure 4 a & b.

• They propose that the history of the CFB in the Western

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Cape is a direct consequence of pre-existing Pan African basemnent structures and two semi-coherent microplates, formed by the intrusion of granitic material into a metapelitic basement.

• Postulate that the largest of the microplates underlies the Southern subdmnain of the Western Branch of the Cape Fold Belt (herein referred to as the Peninsula Microplate) and a second microplate (called the Quoin Point Microplate) situated within the southwestern portion of the Southern Branch of the Cape Fold belt, extending offshore to form part of the Agulas Arch.

• The Syntaxis of the Cape Fold belt can be accounted for by the dextral rotation and N-directed vergence of the Peninsula Microplate, coupled with the sinistral rotation and northward vergence of the Quoin Point Microplate.

Roberts Dating and Preliminary Correlation of Raised Marine and Estuarine Terraces on the Western and Southern Coasts of South Africa, Final Report

2006 Seismic Source

• Dating and preliminary correlation of marine and estuarine terraces on the SA west and south coasts. Also provide stratigraphic overview of Cenozoic coastal deposits.

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Roberts et al. Coastal Cenozoic Deposits 2006 Seismic Source

• This chapter provide an overview of coastal Cenozoic deposits (of littoral marine, estuarine, fluvial, lacustrine and aeolian origin) developed along the coastal plains of the southern African subcontinent.

• These deposits are thin overall, due to the buoyancy of this passive coastline over the past 60 My and erosional events. In contrast, thick Cenozoic deposits have accumulated offshore in extensional rift basins and as sediment cones at major river mouths.

• From a lithostratigraphic standpoint, the southern African coastline has been geographically partitioned according to climatic, oceanographic and tectonic regimes. The Cenozoic Task Group of the South African Committee for Stratigraphy (SACS) has accepted a lithostratigraphic framework for the southeastern coast, southern coast and, to some extent, the southwestem coast. The east coast region is under review and a formalisation of lithostratigraphic tenninology for some units along the west coast from the Verlorevlei River to the Orange River (the "West Coast Group") has recently been proposed.

• Refer to the South African coastline as being passive for the last 60 My.

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Scheepers & Schoch

The Cape Granite Suite 2006 Seismic Source

• Overview chapter confirming the Late Precambrian to

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Early Cambrian age of the Cape Granite Suite.

Shone Onshore Post-Karoo Mesozoic Deposits

2006 Seismic Source

• Overview chapter on onshore, Jurassic and Cretaceous sequences.

• Several scattered complex graben and halfgraben basins developed along the margins of the African continent in response to regional extension associated with the break-up of Gondwana.

• They include the Riversdale, Mossel Bay, Oudtshoorn, Gamtoos and Algoa Basins. The Algoa Basin is the largest of these and has the most diverse sediment fill (i.e. the Uitenhage Group which comprises of the Enon, Kirkwood and Sundays River Formations).

• The Oudtshoorn and Gamtoos Basins are the largest Mesozoic inliers apart from the Algoa Basin, but, unlike the Algoa Basin, only the Enon and Kirkwood Formation equivalents are present in these basins.

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Shone et al. Pre-Cape Rocks of the Gamtoos area – A Complex Tectonostratigraphic Package Preserved as a Horst Block

1990 Seismic Source

• Rocks of pre-Cape age in the Gamtoos area are preserved in an elongate northwest-southeast-trending horst block bounded by the Elandsberg and Gamtoos Faults. The pre-Cape strata have been deformed into a series of recumbent isoclinal folds sliced by a number of southward-dipping imbricate thrusts. Subsequent Cape folding has further affected the pre-Cape rocks, but the pre-Cape and Cape folds are different in style and orientation.

Style of Faulting

• North-south-trending faults (e.g. Boskloof and Otterford Faults) are shown in Figure 2. The latter correspond to 'transfer' faults which form an integral part of horst and graben systems (Gibbs, 1984). This does not mean that the Gamtoos horst is a simple elongated block bounded by contemporaneous faults. It seems more likely that an early line of weakness (the Elandsberg Shear) produced by regional (Pan-African?) extension, allowed the formation of a passive rider which later became a more pronounced horst block during Cretaceous extension (Gamtoos Fault).

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Siegfried et al. The Geology of the Site and the Site Vicinity Areas of Bantamsklip and an Update on Onland Geological Hazards

2008 Seismic Source

• Report comprises mapping of the Bantamsklip Site Area (SA) and Site Vicinity (SV). Major NE-trending faults can be seen on the following 1:50,000 maps:

1. 3419AD Stanford

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2. 3419BC Jongenskip

3. 3419BD Napier

4. 3419CB Gansbaai

5. 3419DA-DC Baarskeerdersbos

6. 3419DB-DD Elim

Smit et al. The Gravity Survey of the Republic of South Africa

1962 Seismic Source

• A report on South African gravity data.

• The Cape Isostatic Anomaly is one of the principle anomalies centredat S33.6° E25.8°.

• The anomaly is consistent with 80 km wide root.

• Site earlier workers who postulated that failure should first occur along the centre line of anomaly and that at a later stage faults with large throws should develop parallel to the centre line at a distance of 50 – 60 km from the centre.

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Söhnge The Worcester Fault 1934 Rupture geometry & Style of Faulting

• Describe the nature and age of the Worcester fault. In general describe dip as 70° - 90°.

• Describe the maximum downthrow to be observed in the Worcester-Robertson area, where he proposes a conservative estimate of 12,500 feet (3810 meters).

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Söhnge The Cape Fold Belt- Perspective

1983 Seismic Source

• Provide an overview of the National Geodynamics Project on the CFB.

• The Cape Fold Belt (CFB) is considered a composite of two orogenies: the Saldanian tectonism of the Pan African event (Hartnady et al., 1974) and the Cape foldings of the Gondwanide orogeny.

• The CFB consists of:

1. A western branch of open, upright megafolds, monoclines and normal faults nearly parallel to the north-north-west strike of the Cape Supergroup from Stellenbosch to Vanrhynsdorp ( -270 km);

2. A southern branch of northward verging folds sliced by thrusts and normal faults trending roughly east-west from Swellendam to Port Alfred (~600 km); and

3. An intervening syntaxis area about 100 km wide with varied upright folds and faults of north-east strike, as between Gordons Bay and Bredasdorp.

• In all three domains the highest ranges are built mainly of quartz arenites of the Table Mountain Group.

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Stankiewicz et Crustal Structure of the 2008 Seismic Source Q4/R4


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al. Southern Margin of the African Continent: Results from Geophysical Experiments

• This paper combines and jointly interprets the different onshore and offshore data sets along the Western Karoo-Agulhas Profile. The model is consistent with the model computed using only onshore shots [Stankiewicz et al., 2007]. The improved ray coverage increased the maximum depth of the model from less than 30 km to almost 40 km, and many of the upper crustal features are better resolved.

• The Moho depth (also see Fig. 11) beneath the Karoo Basin is 40 km, and slightly deeper (42 km) beneath the CFB. The study by Nguuri et al. consistently locates the Moho approximately 5 km deeper than reported here.

• South of the CFB the Moho depth becomes shallower very abruptly, reaching 30 km at the present coast.

• The stretched crust shows a gradual and uniform thinning for another 250 km, underneath the Agulhas Bank, Outeniqua Basin and the Diaz Marginal Ridge, until it reached the Agulhas-Falkland Fracture Zone (AFFZ). This fracture zone marks the continent-ocean transition.

• At this transition (Segment C) the Moho depth of 20 km is reduced to 12 km over a 50 km horizontal distance, through a rapid rise in the Moho.

• The depth of 11–12 km (i.e., 6–7 km of crust under 5 km of ocean) is observed in the Agulhas Passage). The oceanic crust (segment D) on both sections has the global average thickness of about 7 km and a velocity structure that is also typical of oceanic crust worldwide.

Stankiewicz et al.

Initial Results from Wide-Angle Seismic Refraction Lines in the Southern Cape

2007 Seismic Source

• The paper reports the results from two wide-angle on-shore seismic lines roughly parallel to each other approximately 200 km apart, starting at Mossel Bay and St. Francis, and running about 200 km north.

• In both seismic profiles the low-velocity band corresponding to the Karoo Group becomes very thin (< 2km) around 40 km north of the first Witteberg outcrop and is interpreted as a possible blind Paleozoic Thrust Fault, which the authors believe marks the northernmost deformation of the Cape Supergroup.

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Talwani & Eldholm

The Boundary Between Continental and Oceanic Basement at the Margin of Rifted Continents

1973 Seismic Source

• The Agulhas Fracture Zone is interpreted as the margin between the African continental crust and oceanic crust.

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Tankard et al. Crustal Evolution of Southern Africa. 3.8 Billion Years of Earth History

1982 Seismic Source

• See their Figures 1.1 and 1.5 and discussion in Chapter 1 for the proposed position between the NNMB and Saldania tectonic provinces.

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• The upper Witteberg show a transition in type of deposits towards the top of the group, but is still separated from it by a hiatus.

Thamm & Johnson

The Cape Supergroup 2006 Seismic Source

• Overview chapter of the Cape Supergroup.

• The silliclastic Cape Supergroup was deposited in a passive margin setting, that show lateral continuity over 1000 km, over a ~170 My period from the Early Ordovician to Early Carboniferous.

• Provenance was to the north and interpreted depositional environments for the Cape Supergroup range from shallow marine, fluvial and glacial deposits for the basal Table Mountain Group, , wave dominated deltas for the Bokkeveld Group and shallow-marine, paralic and deltaic environments for the Witteberg Groups)

• Stratigraphic thicknesses are also provided, totalling almost 8 km.

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Thomson Role of Continental Breakup, Mantle Plume Development and Fault Reactivation in the Evolution of the Gamtoo Basin, South Africa

1999 Seismic Source

• Mesozoic extensional basins onshore formed by extensional fault system that represent reactivation of Cape Fold Belt thrusts

• Envisage Cape Fold Belt structural control on structure of Gamtoos Basin and larger Outeniqua Basin, but envisage only minor role for the Agulhas-Falkland Fracture Zone on the rotation of the Gamtoos Fault. Latter statement is based on fact that shortening of the southern Gamtoos Basin and substantially more inversion (with possible thrusting of basin fill over the Recife Arch) are not observed.

Rupture geometry & Style of Faulting

• N-S trending Gamtoos Fault is suitably orientated to experience sinistral strike-slip movement with the Gamtoos Anticline forming at a restraining bend in the hanging-wall (McMillan et al., 1997). The inversion and 'pop-up' documented in the St Francis Arch can be accounted for by sinistral strike-slip.

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Toerien Port Elizabeth Sheet. 1986 Fault geometry & Style of Faulting

• Map show NE-SW orientated transfer faults in the CFB.

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Toerien & Robey Oudtshoorn Sheet 1979 Fault geometry & Style of Faulting

• Map show NE-SW orientated transfer faults in the CFB.

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Von Veh Compressional and Extensional Tectonics in the

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Southernmost Exposures of the Cape Fold Belt

• Paper investigates the structural geometry and tectonic history of the southern branch of the Cape Fold Belt in the area between Struisbaai and Danger Point. This area lies at the transition between the southern branch and the syntaxis domain.

• Faults with an ENE trend are most prominent in the study area. They generally cut or swing into alignment with an E-W trending set, as in the case of the Celt Bay fault. Downthrows are mostly to the south. A NW-trending set is poorly represented.

• The ENE-trending fault set is developed in the southern part of the syntaxis domain where an ENE fold trend predominates. The E-W trending normal faults mimic the southward swing of the southern branch as the syntaxis is approached, as illustrated by the Elim fault.

Watkeys Gondwana Break-Up 2006 Seismic Source

• Watkeys provide an overview of continental break-up of Gondwana, describing 5 main stages of break-up with more detailed events described for each stage.

• These include the linkage of fracture systems across Gondwana in the Early Jurasssic and separate development of the southern and western conitnenal margins.

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Weckmann et al. Effective Noise Separation for Magnetotelluric Single Site Data Processing Using a Frequency Domain Selection Scheme

2007a Seismic Source

• Two of the Earth’s largest geophysical anomalies, the Beattie Magnetic Anomaly (BMA) and the Southern Cape Conductive Belt (SCCB) extend across the southern African continent for more than 1000 km in an east-west direction.

• The location of both anomalies parallel to the assumed tectonic boundary of the Namaqua Natal Mobile Belt (NNMB) and the Cape Fold Belt (CFB) provides the basis for an alternative interpretation in terms of tectonic structures related to the accretion process.

• Their model does not account for rock composition or amount of remnant magnetization, it implies that a common source for both geophysical anomalies is unlikely.

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Weckmann et al. Magnetotelluric Measurements Across the Beattie Magnetic Anomaly and the Southern Cape Conductive Belt

2007b Seismic Source

• The results of a high-resolution magnetotelluric study was conducted in March 2004, along a 150-km-long N-S profile across the Karoo Basin in South Africa

• South Africa hosts two of Earth’s largest known continental geophysical anomalies, the Beattie Magnetic Anomaly (BMA) and the near coincident Southern Cape Conductive Belt (SCCB), both of which extend for almost

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1000 km in an east-west direction.

• Based on this work the authors propose that the NNMB basement may extend below the CFB as far as the southernmost continental shelf of Africa.

• They suggest that the conductivity anomaly below the maximum of the BMA is too small to explain the observed SCCB.

Winter Tectonostratigraphy, as Applied to Analysis of South African Phanerozoic Basins

1984. Seismic Source

• Propose that the Karoo Basin and CFB formed as a result of continent-continent collision.

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Table 4.7. Data Evaluation Table 8.3.2 Syntaxis Source Zone (SYN)





p(S)

Seismic Source or

Fault Geometry

Recurrence/Recency & Slip Rate/RI Mmax

Rupture Geometry



Andreoli et al. The Seismotectonic Map

of South Africa, Progress

Report No. 2, Eskom

Seismic Monitoring

Project

1994 Seismic Source

• Detailed mapping of the northwest-oriented faults (see also Von Veh, 1992; De Beer, 2006) may indicate a transition between the east-west- and the north-northwest/south-southeast–striking faults before reaching the core of the syntaxis farther to the northwest (Figure 8.3.2-7).

• Schematically interpreted a transform fault originating at the mid-ocean ridge to project in the direction of the syntaxis

• Documents the abrupt change in regional structural fabric at the syntaxis

Q3/R2

Bate & Malan Tectonostratigraphic

Evolution of the Algoa,

Gamtoos and Pletmos

Basins, Offshore South

Africa

1992 Seismic Source

• This paper summarizes the evolution of the offshore Mesozoic basins.

• These basins developed following reactivation of Late Precambrian and Palaeozoic structures as the result of extension associated with the Jurassic break-up of Gondwana.

Style of Faulting

• Discusses the initiating of normal faulting along pre-existing thrust faults during the Mesozoic

Q3/R1 Q3/R2

Brandt et al. Seismic History of

Southern Africa

2005 Recurrence

• Description of earthquakes associated with the Cape Town Cluster

• Discussion of historical earthquake catalogue

Q4/R2

Broad et al. Offshore Mesozoic

Basins

2006 Seismic Source

• Describe South Africa's continental margins to be a direct consequence of the break-up and separation of the West Gondwana supercontinent. Supercontinental break-up, initiated by extensional forces, commenced in the early Mesozoic. Separation by continental drifting began in the Early Cretaceous and is still continuing today

• Outeniqua Basin is situated of the southern tip of Africa and bounded by the Columbine-Agulhas Arch to the W, the Port Alfred Arch to the E and the Diaz Marginal Ridge to the S.

• Outeniqua Basin comprises a series of rift subbasins including the Bredasdorp, Pletmos, Gamtoos and Algoa sub-basins, separated by fault-bounded basement arches composed of Ordovician to Devonian metasediments of

Q4/R3


432





p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



the Cape Supergroup

• Southern Outeniqua sub-basin is the distal extension of the northem sub-basins below the 300 m isobath

• Algoa sub-basin includes three half-grabens: onshore Sundays River Trough; on & offshore Uitenhage Trough; offshore Port Elizabeth Trough.

• Arcuate trend of the basin-bounding fault systems is most likely inherited from the structural grain of the underlying orogenic Cape Fold Belt (De Swardt & McLachlan, 1982).

• In Fig 1 the E edge of large fault systems coincides closely with the 200m isobath.

• Mesozoic sedimentary fill of the offshore South African rift basins is subdivided into synrift and drift phases of sedimentation:

• The earliest synrift sediments are fluvial and lacustrine in origin, and in some areas are associated with volcanics and volcaniclastics. They are overlain in most basins by deltaic and shallow-marine sediments.

• The drift succession is characterised by deep-marine argillaceous sediments. In the Outeniqua basin the beginning of the drift phase is marked by the 14Atl mid-Albian unconformity

• South Africa's western continental margin is a "passive" volcanic margin and encompasses the greater part of the Orange Basin sensu stricto, as well as a thin, elongate, sedimentary wedge along the the western flank of the Columbine-Agulhas basement arch.

Brown et al. Sequence Stratigraphy in Offshore South African Divergent Basins


• Fault trace is not extended to seafloor (Profile L-L′).

Seismic Source or Fault Geometry

• Fault location (Figure 13).

Q3/R1 Q4/R1

De Beer Simultaneous Folding in

the Western and

Southern Branches of

the Cape Fold Belt


• Presents a history of the folding in the southern and western Cape Fold Belt and the intersection of the two orientations at the Syntaxis. Presents evidence for the contemporaneous development of folding resulting in specific NE oriented fold trends in the Syntaxis.

• Presents orientations of fractures, folds, and faults within the Syntaxis, specifically within the Ceres Arch.

Seismic Source Geometry

• The intersection and mergence of two major structural trends results in the formation of the Syntaxis, an anomalous zone of complexly deformed rocks.

Q4/R4 Q4/R3


433





p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



De Beer Structural Evolution of the Cape Fold Belt Syntaxis and Its Influence on Syntectonic Sedimentation in the SW Karoo Basin

1992 Seismic Source

• The western branch of the CFB (WCFB) displays NW trending open folds without axial plane cleavage, and is transected by numerous faults with approximately the same trend. Megafolds swing progressively into a N-S orientation on approaching the Ceres syntaxis and ultimately become deflected to the SW

• In the E trending folds of the southern branch (SCFB), intense coaxial strains are indicated by the high incidence of second-order folds on megastructure limbs, northward overfolding and thrusting, as well as several cleavage generations.

• The syntaxis is dominated by NE-trending folds of the SCFB, with folds of the WCFB trending N-S.

• The syntaxis is transected at a large angle by the Worcester Fault, causing oblique sinistral displacement of fold axial traces in addition to a 5 km southerly down throw.

• Second-order folds trend NE on the northern limb of the Koo syncline. Further southeast, E-W folds seem to curve continuously into the NE trend of the syntaxis.

• Figures 1 & 2 show that there is a more gradual transition from NE orientated syntaxial folds to E-W southern branch structures.

• In Figure 2 second-order northeast-trending syntaxial folds are shown north of Montagu.

Q4/R4

De Beer Fold Interference From

Simultaneous Shorening

in Different Directions:

the Cape Fold Belt

Syntaxis


• Attributes earthquakes in the Syntaxis to be linked with the westernmost extension of the CKBC fault system.

• Places the M 6.3 1969 Ceres-Tulbagh earthquake on the Groenhof fault (WNW-ESE striking fault). Places three low magnitude events on similar WNW-ESE striking fractures.

Rupture Geometry

• In the SW Cape, WNW-ESE oriented fractures seem to be the most active structures. Within the syntaxis south of the Worcester Fault, seismogenic NE-SW striking faults coincide with deep aquifer fracture systems.

• Maximum compressive stress directions in the SW Cape oriented E-W in the SW Cape Province.

Q3/R4 Q3/R4

De Beer The Geology of the

Ceres Arc, 1:50 000

1999 Seismic Source

• CFB consists of an E-trending fold-thrust branch along the south coast and a less spectacular N-trending branch along the W coast. The two branches overlap in a

Q4/R4


434





p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



scale map syntaxis situated in the SW part of the Western Cape Province.

• Syntaxis is transcended at large angle by WNW striking Worcester fault which caused oblique sinistral displacement.

• shows that the change in fold trend from NW to N in the western branch only occurs in the immediate vicinity of the syntaxis.

• NE trending folds dominate the core of the syntaxis. To the west and north it is replaced by N- and NNW-trending structures. To the east the NE folds merge with the E-trending folds of the Southern branch.

De Beer Association Between Seismicity, Faulting and Regional Stress Directions

2002 Seismic Source

• Figure demonstrates the two CFB branches.


• Summarizes regional stress orientations. In the SW Cape, WNW-ESE oriented fractures seem to be the most active structures. Within the syntaxis south of the Worcester Fault, seismogenic NE-SW striking faults coincide with fracture systems

Q3/R3 Q3/R3

De Beer Investigation into

Evidence for Neotectonic

Deformation Within

Onland Neogene to

Quaternary Deposits

Between Alexander Bay

and Port Elizabeth –

Desk Study Report

2004 Seismic Source

• Overview of the tectonic setting in relation to regional structures during the breakup of Gondwana.

• Description of the syntaxis and surrounding structural characteristics. The author defines the syntaxis as the most fractured part of the Cape Fold Belt.

Rupture Orientation

• Most faults in the area strike northeast-southwest in parallel with fold trends, but some east-west and northwest-southeast faults also are present.

Style of Faulting

• Describes distinction between the evidence for major structure in the SYN zone that formed during the Permo-Triassic versus those that reactivated in the Mesozoic.


• Emphasises that the current seismicity in the Ceres-Tulbagh area is situated where the switchover occurs between the Worcester Fault (with southerly downthrow) and the southwest-striking faults in the graben system near Piketberg such as the De Hoek Fault.

Q3/R2 Q4/R4 Q3/R2 Q4/R4


435





p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



De Beer Investigation into

Evidence for Neotectonic

Deformation Within

Onland Neogene

Quaternary Deposits

Between Alexander Bay

and Port Elizabeth—

South Coast Report


• Possible neotectonic faulting (Figure 42d shows thick scree (unfaulted) over fault.

• Nowhere could the author demonstrate offset of Pliocene or Pleistocene deposits.

Fault Geometry

• Figure 39 is map of extent of Worcester fault.

• Possibly links up offshore with the Plettenberg fault (mentioned in text, but continuous fault not shown on Figure 39).

Recurrence

• Road cut east of Zuurbraak (Figure 41) shows evidence for possible neotectonic reactivation of Worcester fault; two faults, each showing vertical displacement of ~0.5 m, displace channel gravel (unit A) inset into Cretaceous Kirkwood Formation.

• Overlying subhorizontal unconformity between units A and B (terrace gravel deposit) is not deformed.

• Estimated age of most recent faulting is >1.3 Ma based on amount of time estimated for the Tradouw River to incise 20 m below unconformity between units A and B.

Style of Faulting

• Normal reactivation of Cape Fold Belt thrust.

• Steep normal fault with a southerly downthrow.

Q3/R4 Q4/R4 Q4/R5 (lack of evidence for offset of Pliocene and Pleistocene deposits is used to constrain low rate of slip if active)

Q4/R3

De Beer Investigation into Evidence for Neotectonic Deformation Within Onland Neogene to Quaternary Deposits Between Alexander Bay and Port Elizabeth – Executive Summary Report

2006 Seismic Source

• Confirmation that the position of the Kango fault agrees closely with the southern boundary of the Cape Isostatic Anomaly, approximately 50 to 60 km from the centre of this anomaly.

• .Detailed mapping of the northwest-oriented faults (see also Von Veh, 1992; Andreoli et al.,1994) may indicate a transition between the east-west- and the north-northwest/south-southeast–striking faults before reaching the core of the syntaxis farther to the northwest (Figure 8.3.2-7).

Q3/R2

De Villiers A Review of the Cape

Orogeny

1944 Seismic Source

• The Cape system exhibits three main structural lines:

4. The Cedarberg foldings in the west, striking roughly N.N.W.-S.S.E.

5. The Cape foldings in the south with roughly E.-W strike.

6. The Lebombo monocline in the east (not relevant to

Q3/R3


436





p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



this study).

• The Cedarberg foldings extend south-south-eastwards from near Van Rhynsdorp with syn- and anticlines that are open in the north, but becoming more closed towards the south.

• At right angles to this belt there is the southern Cape fold-belt, or Zwartberg foldings, also referred to in a somewhat wider sense, by Du Toit as the Gondwanide orogenic belt. They stretch in a gently curved belt at least 100 miles wide from Worcester in the west to the mouth of the Fish River in the east. In the southern belt the folding is more intense, but decrease towards the east of the southern belt.

• These two tectonic lines met in a region of syntaxis in the Worcester-Ceres area

Du Plessis Seismicity in South Africa and Its Relationship to the Geology of the Region

1996 Seismic Source

• Description of seismicity clusters in South Africa, in particular, the Ceres Seismicity Cluster.

Q3/R1

Green & Bloch The Ceres, South Africa, Earthquake of September 29, 1969: I. Report on Some Aftershocks


• Possible association with Ceres seismicity and Groenhof and De Hoek (also shown on Fig. 39 in De Beer, 2005).

• Historical seismicity within the SYN includes the 1969 Ceres earthquake with an initial magnitude estimate of a 6.3 magnitude and later re-interpreted as a Mw 6.2 ± 0.2 (see also Scherbaum et al., 2011); the less constrained Cape Town cluster concentrated around Cape Peninsula with several M 4–6.3 (Brandt et al., 2005) events in 1809; and the Sutherland cluster ML 4.0–5.3 in February 1952 located at the intersection of northeast- and east-striking folds associated with west-northwest fractures in the syntaxis.

Style of Faulting

• The authors present a focal plane solution for the 1969 Ceres earthquake that indicates a steeply dipping plane showing left-lateral motion on a northwest striking plane.

Fault Geometry

• Author interprets a northwesterly trending Ceres aftershock sequence that suggests the Ceres earthquake may have occurred along the Groenhof Fault within the Cere structural arch. The Groenhof Fault is positioned where the Worcester Fault becomes fragmented in a zone of northwest-striking, near-vertical faults.

Q4/R4 Q4/R2 Q4/R4


437





p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Gresse Worcester Quadrant Geological Map

1998 Fault Geometry

• Compilation map (1:250000) showing extent of mapped trace of Worcester fault.

• Fault does not disrupt remnants of Tg pediments to east of mapped trace.

Q5/R5

Parsiegla et al. Southern Africa Continental Margin: Dynamic Processes of a Transform Margin

2009 Seismic Source

• The authors use 3 types of geophysical data sets collected along two combined seismic land-sea profiles to investigate the deep crustal structure of a transform margin and to characterize processes active at these margins by studying the Agulhas-Falkland Fracture Zone, the Outeniqua Basin, and the Diaz Marginal Ridge.

• Similarities in average (crystalline) crustal velocities for the stretched onshore and offshore continental crust suggest that rocks of the Cape Supergroup underlie the shelf area (beneath the Outeniqua Basin and Diaz Marginal Ridge), consistent with drilling data. Uppermost crustal velocities of between 4.5 and 5.5 km/s (Figure 6b) fit well in the velocity range of the lithologically diverse Cape Supergroup mostly consisting of sedimentary and metamorphically overprinted sedimentary rocks.

• Author describes the thickness change in continental crust from the Cape Fold Belt to the continental margin.

Rupture Geometry


Q4/R1 Q4/R1

Ransome & De Wit

Preliminary Investigations into a Microplate Model for the South Western Cape

1992 Seismic Source

• In this paper the authors speculate that the structural features observed within the syntaxis can be accounted for by the interaction of microplates, formed during the Late Precambrian intrusion of granite suites.

• Two main structural trends are recognised in the southwestern Cape: a N-striking Western Branch of the Cape Fold Belt, and an E-W-striking Southern Branch. The two branches coalesce to produce a NE-striking syntaxis. They consequently recognises three structural domains within the southwestern Cape:

4. Western Branch of the Cape Fold Belt,

5. Southern Branch,

6. An intervening Syntaxis Domain.

• The Western Branch and Syntaxis Domain of the Cape

Q3/R4


438





p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Fold Belt can both be further subdivided into two subdomains. For the position of the syntaxis domains see Figure 1 and Figure 4 a & b.

• They propose that the history of the CFB in the Western Cape is a direct consequence of pre-existing Pan African basemnent structures and two semi-coherent microplates, formed by the intrusion of granitic material into a metapelitic basement.

Scherbaum et al.

Moment Tensor Solution for the 29 September 1969 Ceres Earthquake


• The author reanalyzed focal data from the Ceres earthquake originally presented by Green and Bloch (1971). Reanalysis of the data indicates a moment magnitude (Mw) of 6.2 ± 0.2. Further, the focal mechanism orientation is 124 degrees, dipping 84 degrees to the southwest.

Style of Faulting

• The re-analysis concluded a focal plane solution that indicated strike-slip, left-lateral motion. While there is evidence of deep crustal structural control in this region, the association of the seismicity to a given structure is poorly known.

Mmax

• The largest observed earthquake within the source is the 29 September 1969 Ceres event with Mw = 6.2 ± 0.2

Q5/R5 Q5/R2 Q5/R5

Sohnge The Cape Fold Belt—Perspective

1983 Seismic Source

• Tectonic overview of the Cape Fold Belt. The Cape Fold Belt formed in the Permo-Triassic and is exposed as a mountain chain of 1,200 km along the west and south coasts of South Africa

• On a regional scale, two structural trends are recognised in the Cape Fold Belt of southern South Africa (see also De Villiers, 1944; Ransome & De Wit, 1992). A north-northwest-striking western branch displays relatively open, upright, first-order folds, monoclines, and normal faults An east-west-trending southern branch displays a much higher deformational intensity, as indicated by the north-verging, recumbent first-order folds, a high incidence of second-order folds, and local out-of-the-forelimb thrusting

• The north-trending western branch of the Cape Fold Belt displays relatively open, upright, first-order folds

Q4/R4

Sohnge and Halbich

Geodynamics of the Cape Fold Belt

1983 Seismic Source

• Tectonic overview of the Cape Fold Belt. The Cape Fold Belt formed in the Permo-Triassic and is exposed as a

Q4/R3


439





p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



mountain chain of 1,200 km along the west and south coasts of South Africa

Stankiewicz et al.

Crustal Structure of the Southern Margin of the African Continent: Results from Geophysical Experiments

2008 Seismic Source

• This paper combines and jointly interprets the different onshore and offshore data sets along the Western Karoo-Agulhas Profile. The model is consistent with the model computed using only onshore shots [Stankiewicz et al., 2007]. The improved ray coverage increased the maximum depth of the model from less than 30 km to almost 40 km, and many of the upper crustal features are better resolved.

• The Moho depth (also see Fig. 11) beneath the Karoo Basin is 40 km, and slightly deeper (42 km) beneath the CFB. The study by Nguuri et al. consistently locates the Moho approximately 5 km deeper than reported here.

• South of the CFB the Moho depth becomes shallower very abruptly, reaching 30 km at the present coast.

• The stretched crust shows a gradual and uniform thinning for another 250 km, underneath the Agulhas Bank, Outeniqua Basin and the Diaz Marginal Ridge, until it reached the Agulhas-Falkland Fracture Zone (AFFZ). This fracture zone marks the continent-ocean transition.

• At this transition (Segment C) the Moho depth of 20 km is reduced to 12 km over a 50 km horizontal distance, through a rapid rise in the Moho.

Q4/R2

Stankiewicz et al.


2007 Seismic Source

• The paper reports the results from two wide-angle on-shore seismic lines roughly parallel to each other approximately 200 km apart, starting at Mossel Bay and St. Francis, and running about 200 km north.

• In both seismic profiles the low-velocity band corresponding to the Karoo Group becomes very thin (< 2km) around 40 km north of the first Witteberg outcrop and is interpreted as a possible blind Paleozoic Thrust Fault, which the authors believe marks the northernmost deformation of the Cape Supergroup.

• Author indicates the northernmost onshore Meszoic extension.

Q4/R4

Toerien Oudtshoorn Quadrant Geological Map

1979 Fault geometry

• Compilation map (1:250 000) showing short, discontinuous faults mapped in northwestern part of quadrangle

Q4/R1

Toerien & Hill The Geology of the Port Elizabeth Area,

1978 Seismic Source Q4/R4


440





p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



explanation sheet of map 3324 (scale 1:250 000)

• Fault mapping indicated the northern limit of Mesozoic faulting.

Von Veh Compressional and Extensional Tectonics in the Southernmost Exposures of the Cape Fold Belt

1992 Seismic Source

• The importance of reactivation of pre-existing structures is recognized by the distribution of the late E-W, ENE- and NW-trending extensional faults in and adjacent to the syntaxis domain.

• .Detailed mapping of the northwest-oriented faults (see also Andreoli et al.,1994; De Beer, 2006) may indicate a transition between the east-west- and the north-northwest/south-southeast–striking faults before reaching the core of the syntaxis farther to the northwest (Figure 8.3.2-7).

Q4/R2

1 Sorted by the criteria for identifying the seismic source: probability of activity, source/fault geometry, recurrence, Mmax, or future earthquake characteristics (rupture geometry, style of faulting, and seismogenic

thickness). 2 Quality refers to the degree to which these particular data relate to and provide insights to the SSC model and can be used in its development. Quality (Q1 = low; Q5 = high) 3 Reliance is the degree to which the data provide direct support and justification for particular elements/parameters of the SSC Mode. Reliance (R1 = low, U5 = high)



441

References

Andreoli, M.A.G., Faurie, J.N., Doucouré, M., van Bever Donker, J., Ainslie, L.C., Andersen,

N.J.B., Brandt, D., & McCarthy, T.S. (1994). The Seismotectonic Map of South Africa,

Progress Report No. 2, Eskom Seismic Monitoring Project, March.

Bate, K.J., & Malan, J.A. (1992). Tectonostratigraphic evolution of the Algoa, Gamtoos and



Balkema, Rotterdam.

Brandt, M.B.C., Bejaichund, M., Kgaswane, E.M., Hattingh, E., & Roblin, D.L. (compilers)

(2005). Seismic History of Southern Africa, Seismologic Series 37, Council for Geoscience,

Pretoria, 32 pp.

Broad, D.S., Jungslager, E.H.A., McLachlan, I.R., & Roux, J. (2006). Offshore Mesozoic

basins. In: The Geology of South Africa, M.R. Johnson, C.R. Anhaeusser & R.J. Thomas

(eds.), Geological Society of South Africa, Johannesburg, and the Council for Geoscience,

Pretoria, pp. 553-571.

Brown, L.F., Benson, J.M., Brink, G.J., Doherty, S., Jollands, A., Jungslager, E.H.A., Keenan,

J.H.G., Muntingh, A., & van Wyk, N.J.S. (1995). Sequence Stratigraphy in Offshore South

African Divergent Basins: An Atlas on Exploration for Cretaceous Lowstand Traps by Soekor

(Pty) Ltd., AAPG Studies in Geology #41, 184 pp.

de Beer, C.H. (1990). Simultaneous folding in the Western and Southern branches of the

Cape Fold Belt, South African Journal of Geology 93(4): 583-591.

de Beer, C.H. (1995). Fold interference from simultaneous shortening in different directions:

The Cape Fold Belt syntaxis, Journal of African Earth Sciences 21(1), 157-169.

de Beer, C.H. (1999). The geology of the Ceres arc, 1:50 000 scale map, Council for


de Beer, C.H. (2002). Association Between Seismicity, Faulting and Regional Stress

Directions, Report No. WCU 07-05-2002.



442


Neogene to Quaternary Deposits Between Alexander Bay and Port Elizabeth—Desk Study






Neogene to Quaternary Deposits Between Alexander Bay and Port Elizabeth—West Coast


de Villiers, J. (1944). A review of the Cape Orogeny, Annals of the University Stellenbosch

22(10), 183-208.

Du Plessis, A. (1996). Seismicity in South Africa and Its Relationship to the Geology of the

Region, Report No. 1996-0019, 12 pp., Council for Geoscience, Pretoria.

Green, R.W.E., & Bloch, S. (1971). The Ceres, South Africa, earthquake of September 29,

1969: I. Report on some aftershocks, Bulletin of the Seismological Society of America 61(4),

851-859.

Gresse, P.G., Theron, J.N., Fitch, F.J., & Miller, J.A. (1992). Tectonic inversion and

radiometric resetting of the basement in the Cape Fold Belt. In: Inversion Tectonics of the

Cape Fold Belt, Karoo and Cretaceous Basins of Southern Africa, M.J. de Wit & I.G.D.

Ransome (eds.), pp. 217-228, Balkema, Rotterdam.

Parsiegla, N., Stankiewicz, J., Gohl, K., Ryberg, T., & Uenzelmann-Neben, G. (2009).


Geochemistry, Geophysics, Geosystems 10(3), 20 pp., doi:10.1029/2008GC002196.

Ransome, I.G.D., & De Wit, M.J. (1992). Preliminary investigations into a microplate model

for the South Western Cape. In: Inversion Tectonics of the Cape Fold Belt, Karoo and


Balkema, Rotterdam.



443

Scherbaum, F., Krüger, F., & Reichmann, S. (2011). Moment tensor solution for the 29

September 1969 Ceres Earthquake, PowerPoint presentation at SSHAC Workshop 1, April

13, Cape Town.

Söhnge, A.P.G. (1983). The Cape Fold Belt—Perspective. In Geodynamics of the Cape Fold

Belt, A.P.G. Söhnge & I.W. Hälbich (eds.), pp. 1-6, Special Publication of the Geological

Society of South Africa, 12.

Söhnge, A.P.G., & Hälbich, I.W. (eds.) (1983). Geodynamics of the Cape Fold Belt, Special

Publication of the Geological Society of South Africa, 12, 184 pp.

Stankiewicz, J., Ryberg, T., Parsiegla, N., Gohl, K., Trumbull, R., & Weber, M. (2008).

Crustal structure of the southern margin of the African Plate: Results from geophysical

experiments, Journal of Geophysical Research 113, B10313.

Stankiewicz, J., Ryberg, T., Schulze, A., Lindeque, A., Weber, M.H., & de Wit, M.J. (2007).



Toerien, D.K. (1979). The Geology of the Oudtshoorn Area, explanation sheet of map 3322

(1:250 000 scale), 13 pp., Council for Geoscience, Pretoria.

Toerien, D.K., & Hill, R.S. (1991). The Geology of the Port Elizabeth Area, explanation sheet

of map 3324 (scale 1:250 000), 35 pp., Council for Geoscience, Pretoria.

Von Veh, M.W. (1992). Compressional and extensional tectonics in the southernmost

exposures of the Cape Fold Belt. In: Inversion Tectonics of the Cape Fold Belt, Karoo and


Balkema, Rotterdam.


444

Table 4.8. Data_Evaluation_Table_8.3.3-Karoo Source Zone (KAR)

Author Title Year Relevant Information13 Use for SSC (Quality14/Reliance15)


Probability of Activity


Recurrence/Recency & Slip Rate/RI

Mmax Rupture Geometry (strike, dip)

Style of faulting


Watkeys Gondwana break-up: a South African perspective

2006 Seismic source geometry The right-lateral Agulhas Falkland Fracture Zone (AFFZ) which resulted from the rifting of Gondwana and may have been responsible for incipient rifting propagating into the South Atlantic in the Late Jurassic and early Cretaceous is a 1200 km long transform fault and offset spreading ridges in the South Atlantic and Natal Valley. The AFFZ has been used to delineate the eastern boundary of the KAR zone. The position of the AFFZ is consistent with geophysical data and information from other authors.

Q3:R3

Goodland et al.


1982 Seismic source geometry The orientation of the Agulhas Falkland Fracture Zone (AFFZ) constricted the movement of the Falkland Islands from Africa toward South America. The AFFZ is revealed by magnetic geophysical data. The AFFZ is a good feature to be used as the eastern boundary of the KAR seismic source zone. Making the AFFZ the eastern boundary of the KAR zone is supported by geophysical data and information from other authors (e.g. Watkeys, 2006).

Q4:R4

Chevallier and Woodford

Morpho-tectonics and mechanism of emplacement of the dolerite rings and sill of the western Karoo, South Africa

1999 Rupture Geometry and Style of faulting East-west dextral shear zone in the western part of the KAR zone. This corridor is about 800 km long and 250 km wide. Major north-northwest trending dykes are confined in this corridor. These are offset right laterally by the east-west fissures (now filled by dykes). Dip angles of 85° and 35° have been observed in this area. This paper is one of the few data published and reliance on it was significant. The authors have

Q4:R5 Q4:R5

13

Sort by the criteria for identifying the seismic source: probability of activity, source/fault geometry, recurrence, Mmax, or future earthquake characteristics (rupture geometry, style of faulting, and seismogenic thickness).


Reliance is the degree to which the data provide direct support and justification for particular elements/parameters of the SSC Mode. Reliance (R1=low, U5= high)


445


collected an acceptable amount of data to draw their conclusions.

Thomas et al.


1992 Seismic source geometry The Williston magnetic anomaly separates the magnetically neutral crust of the Saldanian belt from the Namaqua crust which is typified by small but randomly oriented magnetic anomalies. The northern source boundary of the western KAR zone is on the Williston magnetic anomaly. The western boundary of the KAR zone is placed where the Williston and Beattie magnetic anomalies are truncated by the magnetically neutral crust (which may be Pan-African in age) and where the Saldanian province is positioned. Rupture geometry The Beattie magnetic anomaly is the largest east-west trending continental geophysical anomaly. The orientation of this anomaly is used to deduce the rupture orientation in the KAR zone. This is the only known paper found that discusses the Williston anomaly. Information on the Beattie anomaly is also consistent with recent published papers.

Q3:R5 Q4:R4

Du Plessis & Thomas

Discussion on the causative bodies of the Beattie-set of magnetic anomalies

1991 Rupture geometry The Beattie-set anomalies, which are traced from onland to the coast in the southeastern part of South Africa consists of five major anomalies (Empangeni, Durban, Amanzimtoti, Beattie and the Mbashe) that trend in the east-southeast-west-northwest direction. The termination of the Beattie and Mbashe in the west (Cape Province) may indicate the border of the oceanic crust against the continent. Of the five anomalies, the Mbashe and Beattie are in the KAR zone. This information is consistent with data from other published papers.

Q3:R3

Stankiewicz et al.

Crustal structure of the southern margin of the African continent: results from geophysical experiments

2008 Seismic source geometry The change in depth of the Moho in the southern part of South Africa (close to the Beattie anomaly) from 40 km to 30 km is support to the position of the Mesozoic extension toward the coast of South Africa before gently thinning toward the Agulhas fracture zone which marks

Q4:R5


446


the transition zone between the continental and oceanic crust. This change is also close to the boundary between the Cape Fold Belt and the Namaqua-Natal mobile belt. The southern source boundary of the KAR zone is considered to be at the limit of the extended crust. Few data are available that confirm the existence of stretched crust in this area. Geophysical methods have been employed to investigate the thinning of the crust.

Broad et al.

Offshore Mesozoic basins 2006 Seismic source geometry Rifting in the west coast of South Africa, structural complexity and fault severity dissipate in the in-land direction indicating the limit of rifting. Rifting was propagated from south to north along the western coast of South Africa. The limit of the evidence of rifting is used to outline the southern source boundary of the KAR zone. The Agulhas Falkland Fracture Zone (AFFZ) is a transform fault along which the separation of the Falkland Plateau occurred when Africa separated from South America. This demarcates the eastern source boundary of the KAR zone. Few data are available that confirm the existence of stretched crust in this area. However here is a good basis of the positions of the southern and eastern source boundaries to the KAR zone.

Q4:R5



447

References

Broad, D.S., Jungslager, E.H.A., McLachlan, I.R. & Roux, J. (2006). Offshore Mesozoic


(eds.), pp. 553-572, Geological Society of South Africa, Johannesburg/Council for


Chevallier, L. & Woodford, A. (1999). Morpho-tectonics and mechanism of emplacement of

the dolerite rings and sill of the western Karoo, South Africa, South African Journal of

Geology, 102 (1), 43- 54.

Du Plessis, A.J. & Thomas, R.J., (1991). Discussion on the Beattie set of magnetic

anomalies. 2nd Annual Technical Meeting of the South African Geophysical Association,

Pretoria, 57- 59.



Stankiewicz, J., Parsiegla, N. Ryberg, T., Gohl, K., Weckmann, U., Trumbull, R. & Weber, M.

(2008). Crustal structure of the southern margin of the African continent: results from

geophysical experiments. Journal of Geophysical research, 113, doi:

10.1029/2008JB005612.


(1992). Geological studies in southern Natal and Transkei: implications for the Cape Orogen.

In: de Wit, M., Ransome, I. (eds.), pp. 229-236, Inversion Tectonics of the Cape Fold Belt,

Karoo and Cretaceous Basins of Southern Africa. A. A. Balkema, Brookfield.





448

Table 4.9. Data_Evaluation_Table_8.3.4-Cedarville-Koffiefontein Source Zone (CK)







Style of faulting


Goodland et al.


1982 Seismic source geometry The orientation of the Agulhas Falkland Fracture Zone (AFFZ) constricted the movement of the Falkland Islands from Africa toward South America. This is revealed by magnetic geophysical data. The Agulhas Falkland Fracture Zone is a good feature to be used as the eastern boundary of the Cedarville-Koffiefontein seismic source zone. Making the AFFZ the eastern boundary of the CK zone is substantiated by geophysical data and information from other authors (e.g. Watkeys, 2006).

Q4:R3

Jacobs & Thomas

Oblique collision at about 1.1 Ga along the southern margin of the Kaapvaal continent, south east Africa

1994 Seismic source geometry The Natal Metamorphic province (NMP) which is part of the Namaqua-Natal mobile belt is regarded as a Mesopreterozoic ocean arc which collided obliquely with the Kaapvaal craton. In the Natal area, the margin along which this collision took place is considered the southern boundary of the CK zone. Rupture geometry The tectonostratigraphic terranes in the Natal sector of the Namaqua-Natal mobile belt show evidence of prolonged northeast-southwest plate convergence. Structures on the eastern part of the Kaapvaal craton (in the CK zone) have approximately east-west orientation, There are low-angle structures, younger subvertical shear fabrics and subhorizontal to oblique lineations. Subhorizontal compressional tectonics resulted in the thickening of the crust followed by oblique transcurrent shearing within the transport regime. Early phase thrusting displays dip angles ranging from 10-25° (Melville thrust)

Q4:R3 Q3:R3 Q3:R3

16

Sort by the criteria for identifying the seismic source: probability of activity, source/fault geometry, recurrence, Mmax, or future earthquake characteristics (rupture geometry, style of faulting, and seismogenic thickness).


Reliance is the degree to which the data provide direct support and justification for particular elements/parameters of the SSC Mode. Reliance (R1=low, R5= high)


449


and 20° (Mpambanyoni River thrust), both in the Margate terrane. Later transcurrent shear zones (Lilani-Matigulu) in the Tugela terrane show dips of more than 80°. Style of faulting The early thrust tectonics and sinistral transcurrent (strike-slip) shearing are evident in three tectonostratigraphic terranes in the Natal sector of the Namaqua-Natal mobile belt.

Fan & Wallace

Focal Mechanism of a recent event in South Africa: A study using a sparse very broadband network

1995 Style of faulting The 5 October 1986 event in the Cedarville zone (southeast of Lesotho) has normal-slip focal mechanism, similar to the 30 October 1994 event on the southern part of Kaapvaal craton (close to the northwestern border of the Free State Province with magnitude Mw 5.7) and to the 1 July 1976 Koffiefontein event. The Koffiefontein event has two conflicting fault plane solutions; normal-slip faulting dominated by east-west tension stresses (from P-wave movements) and oblique-slip faulting with strike-slip component dominated by east-west principal compressive stresses. Since there is no surface faulting, it is difficult to resolve these solutions. The authors prefer a normal-slip model for the 1976 event. This is one of the few papers in South Africa that talk about focal mechanisms and significant calculations were performed based on the real data available. Rupture geometry The type of focal mechanisms discussed here may be related to the east-west pattern of deformation in southern part of the Kaapvaal craton. Seismicity may also be related to regional uplift. The northeast-southwest trend of seismicity in the Kaapvaal craton may be related to the north-northeast structural trends observed in deep mines. This paper does not discuss the structural geology of the Kaapvaal craton in detail and therefore reliance is not substantial.

Q2:R2 Q4:R5

Brandt & Saunders

New regional moment tensors in South Africa

2011 Style of faulting Information from both tectonic and mine related seismicity indicate that from the focal mechanism solutions

Q4:R5


450


and the faulting regime has changed from normal faulting in the northeast of South Africa (interpreted as a result of crustal stresses associated with uplift and rifting) to strike-slip faulting in the southwest (resulting from ridge pushes from surrounding plate boundaries and/or local crustal thicknesses). The changeover is toward the south western part of the CK zone where the assumption of strike-slip faulting begins and toward the southwest of South Africa (Syntaxis zone). This is one of the few papers that talk about focal mechanisms in South Africa and detailed calculations were performed based on the real data available.

De Wit et al.

Formation of an Archaean continent

1992 Rupture geometry The Colesberg lineament in the CK zone is interpreted a north-south structure along which the Mid-Archaean and the Late Archaean subdomains were sutured. The western and eastern subdomains on either side of the Colesberg lineament have north-south and northeast-southwest structural domains. The orientation of the Colesberg lineament is supported by geophysical data

Q3:R3

Marshall The Natal Group 2006 Seismic source geometry The Natal trough or graben in the eastern part of the CK zone is truncated to the east by the Agulhas Fracture Fault Zone (AFFZ) and only the western portion is preserved along the east coast as the eastern portion was removed during the break-up of the Gondwanaland. The AFFZ is regarded as the eastern seismic source boundary of the CK zone. This is recent data which is consistent with existing information (Goodland et al. 1982)

Q4:R3

Cornell et al.

The Namaqua-Natal Province 2006 Rupture geometry In their map of the Natal sector of the Namaqua-Natal mobile belt, the thrusts, shear zones and lineaments indicate orientation ranging from northeast-southwest to east-northeast dipping toward the south.

Q4:R4

Matthews Possible Precambrian obduction and plate tectonics in southern Africa

1972 Seismic source geometry The border between the Natal crust and the Kaapvaal Craton which is exposed in the Natal sector is marked by major imbricate thrust

Q3:R3


451


zone by which the Tugela terrane was obducted during the Namaqua-Natal orogeny. The Tugela terrane in KwaZulu Natal situated south of the Kaapvaal Craton hosts ophiolites which were obducted on to the craton by a northeast directed thrusting as four major nappes. These large scale inverted metamorphic sequences show that crustal scale thrusting has taken place and support the collision models. The positions of the northern and southern source boundaries of the CK in the east are supported by data from this paper. These data are consistent with information from other papers (e.g. Cornell et al., 2006).

Olivier Geohydrological investigation of the flooding at Shaft 2, Orange-Fish tunnel, north-eastern Cape Province

1972 The Doringberg fault is interpreted to be an area of crustal weakness along the southwestern margin of the Kaapvaal craton. An arcuate belt of gravity highs extending from the Doringberg fault near Prieska to the post-Karoo faults in Lesotho suggest a possible existence of a major fault system which has been reactivated during post-dolerite times. The Doringberg fault is marked as the western source boundary of the CK zone. The Doringberg fault is not the main subject of this paper and therefore data from here is not heavily relied on.

Q2:R2

McCourt The crustal architecture of the Kaapvaal crustal block, South Africa between 3.5 and 2.0 Ga: A synopsis

1995 Rupture geometry The main structural grain on the Kaapvaal craton is east-northeast; this is seen in the orientation of the major greenstone belts on the craton (and also in the orientation of the thrust faults and shear zones in the CK zone). The structural grain in the southwestern part of the craton is in the northerly direction.

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452

References

Brandt, M.B.C. & Saunders, I. (2011). New regional moment tensors in South Africa,

Seismological Research Letters, 82 (1), 69- 80.

Cornell, D.H., Thomas, R.J., Moen, H.F.G., Reid, D.L., Moore, J.M., Gibson. R.L. (2006).

The Namaqua-Natal Province. In: The geology of South Africa, M.R. Johnson, C.R.




Tredoux, M., Peberdy, E., & Hart, R.A. (1992). Formation of an Archaean continent, Nature,

357, 553- 562.

Fan, G. & Wallace, T. (1995). Focal Mechanism of a recent event in South Africa: A study

using a sparse very broadband network, Seismological Research Letters, 66(5), 13- 18.



Jacobs, J. & Thomas, R.J. (1994). Oblique collision at about 1.1 Ga along the southern

margin of the Kaapvaal continent, southeast Africa, Geologische Rundschau, 83 (2), 322-

333.

Marshall, C.G.A. (2006). The Natal Group. In: The geology of South Africa, M.R. Johnson,

C.R. Anhaeusser, R.J. Thomas (eds.), pp. 433- 442, Geological Society of South Africa,




McCourt, S. (1995). The crustal architecture of the Kaapvaal crustal block South Africa

between 305 and 2.0 Ga: A synopsis, Mineralium Deposita, 30, 89- 97.



453

Olivier, H.J. (1972). Geohydrological investigations of the flooding shaft 2 Orange-Fish

tunnel, northeastern Cape Province, Transactions of the Geological Society of South Africa,

75, 197- 224


454

Table 4.10. Data_Evaluation_Table_8.3.5-Namaqua Source Zone (NAM)

Author

Title Year Relevant Information19 Use for SSC (Quality20/Reliance21)






Style of faulting


Viola et al.

Influence of crustal heterogeneity on normal fault dimensions and evolution: southern South Africa extensional system

2011 Seismic source geometry Mesozoic extensional system along the west coast of South Africa is superimposed on a Palaeozoic heterogeneous lithosphere. About 78 to 230km long fault arrays are within this system (which is more than 480km long). These faults show displacements of up to 16 km; they are the longest and show the largest throws and are also high-angle (45 to 60°) normal faults. To the east of this region, there is lack of evidence of Mesozoic extension (western part of the NAM zone). The limit of the fault arrays delineates the western boundary of the NAM zone. Rupture geometry In this region, the orientation of structures ranges from west-northwest-east-southeast to north-northwest-south-southeast. These are different from those in the NAM zone. This article is about the type of structures that are observed outside the NAM zone in the west.

Q4:R5 Q3:R2

Altermann & Halbich

Structural history of the southwestern corner of the Kaapvaal craton and the adjacent Namaqua realm: new observations and a reappraisal

1991 Seismic source geometry At the margin of the Kaapvaal craton are major structures such as the Brakbos and the Brakfontein shear zones. These are truncated at the Doringberg-Hartbees fault zone which is the margin along which the Kaapvaal Craton collided with the Namaqua-Natal mobile belt at about 1.0 Ga, The Doringberg-Hartbees fault zone demarcates the thick Namaqua crust from the

Q3:R3 Q3:R4 Q3:R4

19

Sort by the criteria for identifying the seismic source: probability of activity, source/fault geometry, recurrence, Mmax, or future earthquake characteristics (rupture geometry, style of faulting, and seismogenic thickness). 20

Quality refers to the degree to which these particular data relate to and provide insights to the SSC model and can be used in its development . Quality (Q1=low; Q5=high) Reliance is the degree to which the data provide direct support and justification for particular elements/parameters of the SSC Mode. Reliance (R1=low, U5= high)


455

Author


thin Kaapvaal craton. This therefore forms the eastern boundary of the NAM zone. Rupture geometry and style of faulting There are several deformation episodes in the NAM zone resulted in the main northwest structures which are mainly shear zones and thrusts). Most faults in the NAM zone have steep to sub-vertical dip angles toward the easterly direction. Dip angles ranging from 70° to 80° toward the southwest for some of the right lateral transcurrent thrusts and faults.

Cornell et al.

Namaqua-Natal Province 2006 Rupture geometry Locality map which shows the tectonic division of the Namaqua sector of the Namaqua-Natal mobile belt. The major thrusts and shear zones show there are mostly northwest. Few structures are oriented in the east-west direction.

Q4:R4

Stowe The Upington geotraverse and its implications for craton margin tectonics

1983 Rupture geometry In the NAM zone, northwest shear zones are observed. There are also north-northwest trending fault zones that are associated with the Doringberg fault (lineament). Style of faulting In these faults and thrusts that dominate the NAM zone, right-lateral sense of movement is observed. Although the author does not discuss the orientation of the structures at length, his information is consistent with data from other sources.

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Thomas et al.


1992 Seismic source geometry The Williston magnetic anomaly separates the magnetically neutral crust of the Saldanian belt from the Namaqua crust which is typified by small but randomly oriented anomalies. This is where the southern source boundary of the NAM is. This is the only known paper found that discusses the Williston anomaly. Information on the Beattie anomaly is also consistent with recent published papers.

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Tankard Tectonic evolution of the Cape 2009 Seismic source geometry Q3:R3


456

Author


et al. and Karoo basins of South Africa The Doringberg-Hartbees fault zone separates the thick and young Namaqua crust from the old and thin Kaapvaal craton. This is where the eastern boundary of the NAM zone is placed. This paper does not give the details of the Doringberg-Hartbees fault zone but indicates the type of crust underlies the Kaapvaal craton and the Namaqua crust. This can be used as basis for a seismic source boundary.



457

References




Cornell, D.H., Thomas, R.J., Moen, H.F.G., Reid, D.L., Moore, J.M., Gibson. R.L. (2006).

The Namaqua-Natal Province. In: The geology of South Africa, M.R. Johnson, C.R.



Stowe, C.W. (1986). Synthesis and interpretation of structures along the north-eastern

boundary of the Namaqua tectonic province. South Africa, Transactions of the Geological

Society of South Africa, 89, 185-189.




(1992). Geological studies in southern Natal and Transkei: implications for the Cape Orogen.

In: de Wit, M., Ransome, I. (eds.), pp. 229-236, Inversion Tectonics of the Cape Fold Belt,

Karoo and Cretaceous Basins of Southern Africa. A. A. Balkema, Brookfield.


western margin of South Africa: More than 500 Myr of continued reactivation,

Tectonophysics, tecto-125257, 1- 22.

458

Table 4.11. Data Evaluation Table 8.4.1. Kango Fault Source (KNG)



3)


SeismogenicProbability

p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Clark et al. Australia’s Seismogenic Neotectonic Record: A Case for Heterogeneous Intraplate Deformation

2011 Recurrence/recency & slip rate (analogue)

• Notes that episodic rupture patterns were found in all locations in Australia that had enough paleoseismic data to show a pattern.

• Interseismic intervals for faults may be as long as 20–40 kyr in Western Australia.

Q5/R4

Crone et al. Late Quaternary Surface Faulting on the Cheraw Fault, Southeastern Colorado


• Ages of fault ruptures on the Cheraw Fault in Colorado, USA so evidence of one or more ruptures in 10–15 kyr with periods of low activity >100 kyr in between.

Q4/R3

Crone et al. Paleoseismicity of Two Historically Quiescent Faults in Australia: Implications for Fault Behavior in Stable Continental Regions


• Ages of fault ruptures on faults in South and Western Australia indicate periods of higher activity separated by quiescent periods of 10–100 kyr or more.

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De Beer Investigation into Evidence for Neotectonic Deformation Within Onland Neogene to Quaternary Deposits Between Alexander Bay and Port Elizabeth—Desk Study Report

2004 Seismogenic probability

• Author notes reactivation of Kango Fault along a pre-existing structure and at the southern edge of a gravity anomaly that is at the boundary between the less competent and more competent crust.

Fault geometry

• Notes that the lineament pattern in the Kango fault zone is dominated by conjugate fractures reflecting master joints and minor faults, relict features from the N-S shortening during the Cape Orogeny.

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EPRI Central and Eastern United States Seismic Source Characterization for Nuclear Facilities

2012 Recurrence/recency (analogue for modeling approach)

• Notes the recurrence interval and evidence for clustering for nine faults in the Central and Eastern U.S.

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Goedhart Desk Study Report: A Geological Investigation of Neotectonic Reactivation Along the Ceres-Kango-Baviaanskloof-Coega Fault System in the Southern and Eastern Cape, South Africa


• Notes that the Kango-Baviaanskloof section has the greatest potential for neotectonic reactivation. Described as 118 km of discontinuous scarp 2–4 m high. Although dominantly normal, there is the possibility of sinistral and dextral isolated faults in local step-overs.

• Source of driving force is not well constrained; proposed models as follows:

– Isostatic rebound resulting from rapid retreat of the

Great Escarpment during the Cretaceous (and

Miocene?).

– Uplift of the Eastern Cape coastal region, in relation to

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459



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



the southward upwarping associated with the African

Superswell and extension of the East African Rift

system.

– Possible rotational extension of the easternmost fault

strands resulting from reactivation of the Agulhas

fracture zone. Author favors the isostatic rebound on

the margin of the Willowmore gravity low to explain the

faulting along the Kango.

• Notes that the Ceres-Kango-Baviaanskloof-Coega (CKBC) fault was initially activated in the Paleozoic to Cretaceous. Author infers that this zone of weakness is more likely to be reactivated.

• Stratigraphy (evidence of early [Mesozoic] faulting): Enon Formation (fluvial deposit with TMG quartzite and sand stones) lies on the Jurassic igneous deposits of the Suurberg Group. The early Enon Formation rudite beds are coarse-grained and lie generally to the south of the large boundary faults; bedding generally dips towards the faults, indicating active growth faults at time of deposition.

• Notes that there is an isostatic gravity anomaly coincident with the entire CKBC fault system. The anomaly appears to behave irrespective of lithologic contacts. See Smit (1962).

• Aerial photo interpretations indicate “four base-level lowering events.” Based on topographic position of fluvial terraces (p. 86).

Fault geometry

• Total length (Kango-Baviaanskloof): 118 km.

• Dip: 45° (measured from calcretised fault plane exposed at Buffelsvalley Farm).

Goedhart A Geological Investigation of Neotectonic Reactivation Along the Ceres-Kango-Baviaanskloof-Coega Fault System in Southern and Eastern Cape, South Africa: Field Reconnaissance Report


• Recognises the Kango Fault as the only Quaternary fault in South Africa

Style of faulting

• Dip-slip/normal down to the south.

Fault geometry

• This is the follow-up study to the 2004 desk study of De Beer. The field findings shortened the total length of the fault to approximately 84 km.

• Dip: 45° in bank exposure (site M1.26 river site).

Fault geometry (length and segmentation) (Mmax inputs)

• The active Kango Fault is split into two sections: the 45 km long western arm (10 km east of De Rust at site M1.19

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Q3/R3-4 (eastern-western part, respectively)

Q3/R2

Q4/R4


460



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p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



to Toorwaterpoort (hot spring activity at Toorwaterpoort, site 1.91) and the 41 km long eastern arm (site 1.91 to site 1.133). Acknowledges these as provisional subdivisions.

• Scarp heights (not corrected to represent net vertical tectonic slip) range from 1 m to 8.5 m. Scarps are higher on the interfluves surfaces (5–8.5 m) and lower scarp heights in the lower-lying alluvial valleys (1–4.5 m, but typically 3–4.5 m). Cumulative events are inferred by the differing scarp heights.

• Provisional subdivisions considered as possible rupture segments.

Recurrence/recency & slip rate

• “Paleosol” (dated to 4,660 ± 40 yr BP. The paleosol is used as a “maximum age for reactivation”. The sample was taken from a zone in the outcrop 0.6 x 2 m, not from a single discrete sample. Holocene event ≤4336 BC. (Note: paleoseismic trenching shows that this dated unit post-dates the most recent event [Hanson et al., 2012b]).

• P. 21 discusses a possible “actual age of 5,316 years.” It is unclear whether this is a calibrated date; nonetheless, this is the date used to determine the slip rate of 0.66 mm/year.

• Site M1.57 is a pre-existing bulldozed trench, <2 m deep roughly parallel to the Kango Fault trace. The trench exposes liquefaction features dated to 5,530 ± 45 yr BP. A spring is located at this site along the scarp.

• Site 1.91 (Toorwaterport): natural exposure showing unfaulted deposits dated to 13,210 ± 60 yr BP. Acknowledged uncertainty that the deposits could be re-precipitated after fracturing in a faulting event and thence “healing” the fractures.

• Kango Fault west of De Rust: Six sites were visited between the Touws River and De Rust. Generally, the findings were that there were no disturbances to the Quaternary deposits in the vicinity of the fault trace. No age dating or relative age estimates for the undisturbed Quaternary deposits were provided by the author. At one site near the Prinsrivier Dam, the author suggests that recent rock fall could have been triggered by a seismic event.

Goedhart A Geological Investigation of Neotectonic Reactivation Along the Ceres-Kango-Baviaanskloof-Coega Fault System in the Southern and Eastern Cape, South Africa:

2006 Paleoseismic trench report. Trench was 80 m long x 6 m

wide x 2.5 m deep. All surface deformation occurred within a

32 m wide graben.


• Single event—Deformation is well bracketed to have

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(See Hanson et al., 2012b, for re-interpretation.)

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461



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p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Trench Report occurred between 12,206 and 8,878 yr BP.

Fault geometry

• Total length: 85 km.

• Dip: 67° (trench exposure).

Recurrence/slip rate

• The oldest dated unit near the floor of the trench is 108 ka, suggesting a recurrence interval of at least this long. The author goes on to conclude that the basal units appear to be flat-lying deposits; therefore, there was no PE scarp at the time of the deposition of the 108 ka unit. The author cites the “Machette Criterion” for scarp erosion rate in the semiarid region of the southwest, which estimates 100 ka to erode a scarp completely. Therefore, the author concludes that the PE could be as old as 100 ka + 108 ka = 208 ka.

• A maximum slip rate of 0.0187 mm/year is estimated.

• Using an assumed age of 2 Ma (not well constrained) for the oldest offset straths across the eastern part of the fault zone, the long-term slip rate is 0.00375 (7.5 m scarp/~2 Ma).

• The author notes the thickening of unit 2a in the southern margin of the graben. This observation infers that there is an antithetic fault not observable in the trench. This could be interpreted as a penultimate fault (p. 52).

• Timing of the MRE is constrained between 8,878 ± 452 ky BP) (E26-S1A) and 12,206 ± 723 kyr BP (B17-S1A). This conclusion may stem from the author’s unintentional interchanging of sample numbers, referring to sample B17-S1A also as B7-S1A for many pages. Sample B17-S1A is problematic because it is stratigraphically higher yet older than underlying units. The author states that the large scatter in sample B17-S1A suggests the date is not precise, but should be considered a maximum age of the MRE nonetheless. The author prefers a MRE bracketed between 10,167 ± 507 kyr BP (F15-S1A) and 10,327 ± 755 kyr BP (F27-S1A). There are other ages suggested by doing different age analysis approaches, such as taking the mean of three similar ages, etc. The general conclusion is that the MRE occurred ~10 ka and not before ~12 ka.

• Author suggests that the basal trench units could correlate to marine oxygen isotope stage (MIS) 5e.

• Report concludes that “since the beds above and below the disconformity are equally offset by the MRE, there was no other faulting during the 105 ka erosion period”.

Mmax (segmentation)

• Report expresses uncertainty that the eastern and


462



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



western traces of the Kango Fault could rupture independently. Rupture Length: either 85 km or 45 km.

• Maximum offset measured was 2 m by projecting the fan slope surface across the main trace of the fault and the south-bounding graben.

• Author notes some large scarps on the eastern segment, which could suggest segmentation.

• Author reports that all the units in the trench below the most recent event (MRE) horizon are offset by the same amount, thus suggesting only one event is exposed in the trench. (See Hanson et al., 2012b, for reinterpretation.)

• Report estimates a Mmax from M 7.18 to M 7.43. References Partridge (1995), who estimated a M 8.7.

Goedhart Palaeoseismic Characteristics of the Kango Fault and Associated Uncertainties, Coega Fault Style &Potential CFB SSZs

2012 PowerPoint presented at TNP SSHAC 3 Workshop 2. Summary of previous reports and publications.


• References earlier studies indicating evidence for Holocene activity.

Fault geometry

• Presentation has a focus on rupture length for the Kango Fault.

• Discussion of uncertainties in endpoints for reactivated fault.

• Eastern boundary of the Kango Fault is suggested to be at the Baviaanskloof thrust (also the Kilpadbeen boundary) or slightly farther west of the thrust.

• Notes possible step-over splays at Skilpadbeen boundary.

• Dip: Fault dip at site M1.42 is 65°–75° to the south.

Recurrence

• Preferred MRE between 10.6 and 10.3 ka.

Mmax

• In all scenarios of rupture segments, sites M1.26 and M1.42 are in the same segment.

• Segmentation model notes unfaulted 13 ka deposits at site M1.91; however, there is uncertainty as to whether the bedrock fault is under the unfaulted package of alluvium.

• Total length of combined western and eastern arm is ~84 km ± 10 long.

• Notes fault dip at site M1.42 was 65°–75° to the south.

• Estimates vertical surface offset at M1.42 to be 2.0 m (single event).

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463



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Goedhart & Booth

Early Holocene Extensional

Tectonics in the South-

Eastern Cape Fold Belt,

South Africa


• 84 km long extensional surface rupture; 10,620 ± 509 years ago, based on OSL ages.

Fault geometry

• Total length is 320 km.

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Goedhart & De Klerk

A High-Resolution Multi-

Electrode Resistivity Survey

to Investigate a Neotectonic

Rupture Along the Kango

Fault, Near Oudtshoorn,

Southern Cape Fold Belt,

South Africa

2011 Fault geometry

• Provides constraints on the geometry of the Kango Fault in the upper 70 m.

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Investigations—Kango Fault

Study

2012b Seismogenic probability

• The 92–101 km long eastern segment of the Kango Fault west of De Rust appears to be unique among faults within the Ceres-Kango-Baviaanskoof-Coega fault system in that it shows evidence for repeated surface-faulting events during the Quaternary.

• Paleoseismic investigations at the M1.26 site document evidence for two latest Pleistocene to Holocene surface-faulting events. The timing of the penultimate event (PE) and most recent event (MRE) at this site is constrained by C14 and OSL ages to be between 15 and 10 ka (most likely between 13 and 10.3 kyr BP [referenced to AD 1950] and 4.5 ± 0.4 kyr BP).

• Additional dating of samples previously collected from the M1.42 trench, combined with re-evaluation of photodocumentation of the excavation wall at the M1.42 site, suggests that these two events also are recorded in the statigraphic and structural relationships observed in the M1.42 trench. The constraints on timing from the M1.42 trench suggest that the PE occurred between 12 and 10.9 yr BP, and the MRE event occurred 6 ± 0.5 kyr BP. This interpretation conflicts with the previous conclusion that the M1.42 trench recorded a single surface-rupturing event approximately 10 ka.

• The youngest faulting at the M1.133 site in the eastern section of the reactivated Kango Fault appears to have occurred between 22.6 and 25.4 ka. This estimated age is based on CN analysis of a series of samples taken from the scarp face at this site.

Geometry

• The length, segmentation, and geometry of the

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p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Quaternary active Kango Fault are largely inherited from structures initially formed during the Permo-Triassic Cape Orogeny that were reactivated during the breakup of Gondwana in the Mesozoic and subsequent rifting of the South Atlantic.

• Remapped active trace using DEM, aerial photographs, and GoogleEarth images.

Recurrence (timing and slip rate)

• Temporal clustering—The two most recent surface-rupturing events at the M1.26 and M1.42 sites were preceded by a long period of several tens of thousands of years of no activity (at least 63–123 kyr or longer).

• Long-term slip rate—A long-term vertical displacement and slip rate were measured across the western part of the Quaternary-reactivated Kango Fault at the M1.42 site. Cumulative net vertical separation of erosional surfaces (pediment or strath terraces) formed on top of bedrock in the hanging wall and footwall of the fault zone at this site ranges from 26 m to as much as 33.4 m. CN burial ages of clasts within alluvium overlying the erosional surfaces range from 0.6 to 3.2 Ma, with short (19–121 kyr) periods of initial exposure before burial. Within the resolution of the CN burial dating method, the burial ages for the gravel deposits directly overlying the erosional surface on the hanging wall (2.2–3.2 Ma) cannot be differentiated from the burial age of the basal gravel from the footwall (2.1 Ma). Using an age estimate of 2.5 ± 0.6 Ma for the displaced basal gravel unit, and a net vertical separation of 26–33.4 m yields a long-term vertical slip rate ranging from 0.008 to 0.018 mm/yr for the Kango Fault at the M1.42 site.

• Long-term slip rate—Cumulative net vertical separation of the erosional surface of the Tertiary gravel (Tg) pediment remnants that are displaced by the Kango Fault in the easternmost reach of the reactivated fault (at the M1.30 and M1.33 sites) ranges from 5 to 9 m. The long-term cumulative slip on the fault at the eastern end appears to be less than what is observed at the M1.42 site (26–33.4 m) from interpretation of boring data, or at the M1.35 site (minimum of 11.4 ± 4 m, inferred offset across younger and older scarps in Tg surface).

• Estimated long-term vertical slip rates at the M1.133 site range from a value of 0.012–0.025 mm/yr (based on the assumption that the 10Be exposure age [0.36–0.38 Myr] for the boulders represents a minimum limiting age of the Tg surface that is displaced 7 ± 2 m across the entire fault zone), to a lower value of 0.001–0.01 mm/yr (based on the assumption that the Tg surface records cumulative slip over a longer period of 1–4 Ma).


465



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



• At the M1.133 site, strata within the Tg deposits may be offset by an amount similar to that of the surface offset on the main fault in the youngest zone of faulting. CN analysis of one of the six clasts that were collected from within a fissure near the fault scarp, where it presumably was shielded from cosmic rays by several metres of silcrete, suggests that the Tg clast was deposited many 10Be half-lives ago (10Be half-life ~1.4 Myr); this age is consistent with the estimated age (7–9 Ma) of Tg silcrete in the Oudtshoorn Basin.

• Assuming that the cumulative slip postdates the formation of caprock across the entire fault zone, the long-term slip rate at the M1.133 site would be as low as 0.0007–0.001 mm/yr (7 ± 2 m/7–9 Ma, based on electron spin resonance ages for Tg silcrete in the Oudtshoorn Basin).

Mmax

• Alternative rupture scenarios are considered in estimating the maximum magnitude of expected ruptures for the Kango Fault, as follows: 30 km (the length of the western reach of the Kango Fault with clear evidence of two latest Pleistocene to Holocene surface ruptures); 50 km (the length of the western part of the reactivated fault zone from the endpoint near De Rust to Toorwaterpoort gorge that shows geomorphic evidence for a possible continuous Holocene scarp); and 92 km (the length of the fault with evidence of Quaternary surface faulting).

• Average displacement per event for the two most recent surface-faulting events is best constrained at the M1.26 and M1.42 trench sites. Evidence for cumulative net vertical separation of 2–3 m from two events at these sites suggests an average vertical displacement of 1–1.5 m per event. Net tectonic slip per event based on an assumed fault dip of 45°–70° at depth would be 1–2 m.

• Empirical relationships relating moment magnitude (M) to rupture characteristics (i.e., rupture length, rupture area, and average displacement) that have been developed from data specific to stable continental regions, as well as more active regions, were used to estimate the maximum magnitude of paleoearthquakes that have occurred on the Kango Fault. The estimated magnitudes range from approximately M 6.6 to M 7.6; values in the range of M 7.0 to M 7.4 are preferred estimates based on rupture areas defined by seismogenic depths of 15–17 km and average displacement-per-event data.

Hill Quaternary Faulting in the South-Eastern Cape Province


• Article describes late Quaternary reactivation of the Kango-Bavianskloof fault system.

• Scarp height does not exceed 5 m.

Q3/R3 Q3/R3 Q3/R3


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p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



• Attributes alluvial fans that cross the fault as the result of episodic heavy downpours. Suggests an age of Quaternary, or possibly during the late Pleistocene hypothermal with its increased precipitation.

Fault geometry

• ~100 km. The length for the reactivation is also described as “confined to the De Rust–Antoniesber segment of the fault”, which is ~50 km long. (p. 401)

Style of faulting

• En echelon scarps observed across high terrace at the farm Annex Misgaad 18 (Fig. 6) are suggestive of shear deformation (left-lateral); however, due to the restricted occurrence of this phenomenon, an alternative explanation may be that the incoherent and inhomogeneous cover material may be responsible for differential transmission of youngest fault displacement.

Le Roux Geodynamics of the Cape Fold Belt


• Author notes that the Kango Fault in general is the contact between the Enon Formation on the south side and the Kango Group to the north. There is a note that a Tertiary surface overlies the fault and has a faint trace visible on aerial photos, suggesting post-Tertiary offset.

Recurrence/recency & slip rate/RI

• Post-Tertiary.

Q3/R1 Q2/R1

Leonard Earthquake Fault Scaling: Self-Consistent Relating of Rupture Length, Width, Average Displacement, and Moment Release

2010 Mmax (empirical relationships)

• Proposes self-consistent scaling relations between seismic moment, rupture area, length, width, and average displacement on a fault.

Q4/R4

Lindeque et al. Deep Crustal Seismic Reflection Experiment Across the Southern Karoo Basin, South Africa

2007 Seismogenic thickness

• >10 km.

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McCalpin Field Reconnaissance and Seismic Source Characterization of the Kouga, “Paul Sauer”, Kango, and Baviaanskloof Fault Zones, Cape Fold Belt, Republic of South Africa

2009a Report summarises the findings of a three-week field reconnaissance in the Eastern Cape Fold Belt to assess evidence for Neogene reactivation on several faults, including the Kango Fault.


• Notes late Pleistocene to Holocene activity on the Kango Fault.


• Author identifies a single-event recent fault scarp in Quaternary deposits (1.5–2 m) and larger fault scarps (5.2–11.7 m) on Tertiary surfaces. Uses the single-event

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467



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



scarp to estimate four to nine post-Miocene surface ruptures to yield a long-term recurrence interval slip rate.

• Uncertainty is affected by the age of the Tertiary surface and the time span during which the ruptures occurred. Due to these uncertainties, the author recommends simplified probability density functions for most of the seismic source characterisation.

• Estimated the age of site M1.50 displaced fan.

Mmax (segmentation and displacement per event)

• Six sites were visited along the Kango Fault where topographic profiles were measured across the fault zone to estimate cumulative net vertical separation (throw).

• At site M1.50, the displaced fan (~1.5 m net vertical separation) is estimated to be ~100 ka.

• At site M1.35, an old and a young scarp are separated spatially by 500 m; the young scarp is to the south.

• At site M1.33 are an old and a young scarp; the young scarp is south of the old one.

• Author concludes that the total length of the fault (~80 km) is too long to correlate with the measured “single-event” displacements. Rather, the surface rupture lengths predicted from field measurements suggest shorter rupture lengths that roughly agree with the segment lengths of the western (45 km) and eastern (35 km) segments. The author supports this by citing Goedhart (2006), who infers the ages of the MRE on the western and eastern segments as considerably different.

• Suggests that the segments rupture independently.

Rupture geometry (strike, dip)

• Dip-slip/normal down to the south.

Partridge A Review of Existing Data on Neotectonics and Palaeoseismicity to Assist in the Assessment of Seismic Hazard at Possible Nuclear Power Station Sites in South Africa


• Document summarises previous work conducted in South Africa.

• Document cites Hill (1988) for recognising a 4 m high fault scarp.

• Deposition of the offset alluvial fans could be correlative to periods of elevated precipitation levels during marine oxygen isotope stage (MIS) 3 (60–21 ka) and the warming that followed the waning of the Last Glacial Maximum (~16–12 ka; Partridge, 1990). By extension, this document suggests that the offset is post-60 ka.

Q3/R3


468



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Paton Influence of Crustal Heterogeneity on Normal Fault Dimensions and Evolution: Southern South Africa Extensional System

2006 Paper discusses the structural evolution of South Africa’s extensional fault system post-Mesozoic.

Fault geometry

• Article cites Hälbich (1993) as suggesting that the normal faults of the Cape Fold Belt may sole into a mega-décollement around 40 km deep.

Mmax (segmentation)

• Presents a model for coalescing fault-bound basins that contain interbasin highs. With this model, fault arrays are composed of a number of coalesced segments that have a linear, rather than en-echelon, trench.

• Subdivides the 230 km long Kango Fault into five discernable segments. The western end of the fault is near Ladismith, and its eastern limit is southwest of Willowmore.

• Does not call out any active segment, but the active segment cited by others is split into at least three segments, which are 30, 20, and 20 km long from west to east.


• Dip: 60° south (p. 877).

• Estimates dips on neighboring Plettenberg and Gamtoos Faults as 65° and 42.5°, respectively.

Q4/R4 Q3/R3

Paton et al. Applicability of Thin or Thick Skinned Structural Models in a Region of Multiple Inversion Episodes; Southern South Africa

2006 Seismic source or fault geometry

• The paper states that the southern Cape region of South Africa has undergone at least two episodes of structural inversion: first, compression forming the Cape Fold Belt; subsequently, extension in the Mesozoic. Fault geometry has remained constant in both episodes.


• Structures dip between 24° and 60°. The south is composed of higher-angle faults, whereas the north is composed of shallower-dipping faults.


• Broadly, the model classifies the crust north of the Swartberg Mountains, in the great Karoo, as “thin skinned” and south as “thick skinned.” However, the paper also states that the Cape Fold Belt cannot be classified as thick- or thin-skinned; rather, it is more useful to describe the deformation as being controlled by a south-dipping mega-decollement that exhibits aspects of both end members.

Q3/R3

Stankiewicz et al.

Initial Results from Wide-Angle Seismic Refraction

2007 Geometry (strike, dip)

• Dip steeper to the east and more listric to the west, where

Q4/R4 Q4/R4


469



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Lines in the Southern Cape dip is shallower and flatter (Fig. 4).


• In the west, the Kango Fault is traced to ~12 km with seismic refraction.

• In the east, the Kango Fault is traced to ~14 km with seismic refraction.

Stankiewicz et al.

Crustal Structure of the Southern Margin of the African Continent: Results from Geophysical Experiments

2008 Geometry (strike, dip)

• Low dip, listric at 10–12 km (Figs. 5 and 12).

Q3/R4

Toerien The Geology of the Oudtshoorn Area, Explanation Sheet of Map 3322 (1:250 000 scale)


• Shows displaced Grahamstown Formation (Tg).

Geometry

• Location of bedrock fault.

Q3/:R2 Q3/R3

Toerien & Hill The Geology of the Port Elizabeth Area (Explanation of Map 3324)

1989 Geometry

• Location of bedrock fault.

• Length.

Q3/R3

Toerien & Roby Oudtshoorn Quadrant Geological Map

1979 Fault geometry

• Fault location.

Q3/R4

Umvoto Deep Artesian Groundwater for Oudtshoorn Municipal Supply Phase D Target Generation & Borehole/Wellfield Siting Using Structural Geology and Geophysical Methods

2005 Geometry

• Map location (Fig. 3.4).

Mmax (segmentation)

• The Schoemanshoek–De Rust fault bend, the Stompdrift fold, and other minor faults exposed at surface to the SE of De Rust, are parts of a complex “accommodation” or “transfer” zone between two major segments of the Kango Fault. The Stompdrift accommodation zone would have formed at a relatively late state in the evolution of the Kango fault system, when formerly separate en-echelon segments became linked, and their displacement fields began to interfere via the development of cross-faulted and cross-folded structures, parts of which may now be buried beneath the Cretaceous strata to the west of the Toorfonteinkloof fault bend.

Q4/R4 Q4/R3

Wells & Coppersmith

New Empirical Relationships Among Magnitude, Rupture Length, Rupture Width, Rupture Area, and Surface Displacement

1994 Mmax (empirical relationships)

• Uses historical earthquakes to develop empirical relationships between moment magnitude, surface rupture length, downdip rupture width, and average surface displacement.

Q4/:R4

Wesnousky Displacement and 2008 Mmax (empirical relationships) Q4/R4


470



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Geometrical Characteristics of Earthquake Surface Ruptures: Issues and Implications for Seismic-Hazard Analysis and the Process of Earthquake Rupture

• Uses statistics on approximately three dozen historical earthquakes to compare observations of surface slip along strike.

1 Sort by the criteria for identifying the seismic source: probability of activity, source/fault geometry, recurrence, Mmax, or future earthquake characteristics (rupture geometry, style of faulting, and seismogenic thickness).



471

References

Clark, D., McPherson, A., & Collins, D.C.N. (2011). Australia’s seismogenic neotectonic

record: A case for heterogeneous intraplate deformation: Record 2011/11. Geoscience

Australia, Canberra.

Crone, A.J., Machette, M.N., Bradley, L., & Mahan, S.A. (1997). Late Quaternary Surface

Faulting on the Cheraw Fault, Southeastern Colorado: U.S. Geological Survey Geologic

Investigations Map I-2591, includes 7 pp. pamphlet.

Crone, A.J., De Martini, P.M., Machette, M.N., Okumura, K., & Prescott, J.R. (2003).

Paleoseismicity of two historically quiescent faults in Australia: Implications for fault behavior

in stable continental regions, Bulletin of the Seismological Society of America 93(5), 1913–

1934.




Electric Power Research Institute (EPRI), U.S. Department of Energy, & U.S. Nuclear

Regulatory Commission (2012). Technical Report: Central and Eastern United States

Seismic Source Characterization for Nuclear Facilities, 6 volumes.


Reactivation Along the Ceres-Kango–Baviaanskloof-Coega Fault System in the Southern

and Eastern Cape, South Africa, Report No. 2004-0189, Eskom NSIP-SHA-013852#P1-153,

129 pp., Council for Geoscience, Pretoria.



Africa: Field Reconnaissance Report, Report No. 2005-0084, Eskom NSIP-SHA-

015892#P1-133, 167 pp., Council for Geoscience, Pretoria.



Africa: Trench Report, Report No. 2006-0085, Eskom NSIP-SHA-018229#P1-286, 302 pp.,




472

Goedhart, M.L. (2012). Palaeoseismic characteristics of the Kango fault and associated

uncertainties, Coega fault style & potential CFB SSZs, slide presentation at SSHAC L3

Workshop 2, Spier, Cape Town, South Africa, January 15–18.

Goedhart, M.L., & Booth, P.W.K. (2009). Early Holocene extensional tectonics in the south-

eastern Cape Fold Belt, South Africa, paper presented at Ancient Rocks to Modern

Techniques, 11th South African Geophysical Association (SAGA) Biennial Technical

Meeting and Exhibition, Inkaba yeAfrica Phase II workshop, September 16, Manzini,

Swaziland.

Goedhart M.L., & de Klerk, M. (2011). A high-resolution multi-electrode resistivity survey to

investigate a neotectonic rupture along the Kango fault, near Oudtshoorn, southern Cape

Fold Belt, South Africa, unpublished report by Kainos South Africa and Cape Geophysics

submitted to the Council for Geoscience: Report No. KSA-2011-0003, 26 May 2011.

Hälbich, I.W., 1993. The Cape Fold Belt–Agulhas Bank transect across Gondwana Suture,

Southern Africa, Global Geoscience Transects 9, 20 pp., American Geophysical Union,

Washington, D.C.

Hanson, K., Slack, C., & Coppersmith, R. (2012b). Thyspunt Geological Investigations—

Kango Fault Study, Report No. 2012-0035, Rev. 0, 43 pp., Council for Geoscience, Pretoria.

Hill, R.S. (1988). Quaternary faulting in the south-eastern Cape Province, South African

Journal of Geology 91 (3), 399–403.


average displacement, and moment release, Bulletin of the Seismological Society of

America 100(5A), 1971-1988.

Le Roux, J.P. (1983). Structural evolution of the Kango Group. In: Geodynamics of the Cape

Fold Belt, A.P.G. Sohnge & I.W. Halbich (eds.), The Geological Society of South Africa,

Special Publication No. 12, ch. 5, pp. 47-56.

Lindeque, A.S., Ryberg, R., Stankiewicz, J., Weber, M.H., & de Wit, M. (2007). Deep crustal

seismic reflection experiment across the southern Karoo Basin, South Africa, South African

Journal of Geology 110(3), 419-438.



473

McCalpin, J.P. (compiler) (2009a). Field Reconnaissance and Seismic Source

Characterization of the Kouga, “Paul Sauer”, Kango, and Baviaanskloof Fault Zones, Cape

Fold Belt, Republic of South Africa, Report No. 2009-0235, Council for Geoscience, Pretoria.

Partridge, T.C. (1990). Cainozoic environmental changes in Southern Africa, Suid-

Afrikaanse Tydskrif vir Wetenskap 86, 315–317.

Partridge, T.C. (1995). A Review of Existing Data on Neotectonics and Palaeoseismicity to

Assist in the Assessment of Seismic Hazard at Possible Nuclear Power Station Sites in

South Africa, prepared for the Council for Geoscience, 42 pp.


evolution: Southern South Africa extensional system, Journal of Structural Geology 28(5),

868-886, doi:10.1016/j.jsg.2006.01.006.

Paton, D.A., Macdonald, D.I.M., & Underhill, J.R. (2006). Applicability of thin or thick skinned

structural models in a region of multiple inversion episodes: Southern South Africa, Journal

of Structural Geology 28(11), 1933-1947.

Smit, P.J., Hales, A.L., & Gough, D.I. (1962). The Gravity Survey of the Republic of South

Africa, Geological Survey of South Africa, Handbook 3, 486 pp.

Stankiewicz, J., Ryberg, T., Schulze, A., Lindeque, A., Weber, M.H., & de Wit, M.J., (2007).



Stankiewicz, J., Ryberg, T., Parsiegla, N., Gohl, K., Trumbull, R., & Weber, M. (2008).

Crustal structure of the southern margin of the African Plate: Results from geophysical

experiments, Journal of Geophysical Research 113, B10313.

Toerien, D.K. (1979). The geology of the Oudtshoorn area—Explanation of Sheet 3322

(1:250 000 scale), Geological Survey of South Africa, Pretoria, 13 pp.

Toerien, D.K., & Hill, R.S. (1991). The Geology of the Port Elizabeth Area, explanation sheet

of map 3324 (1:250 000 scale), 35 pp., Council for Geoscience, Pretoria.



474

Toerien, D.K., & Roby, D.J. (compilers) (1979). Oudtshoorn quadrant geological map,

1:250 000 scale, compiled from 1:125 000 sheet Gamkapoort–Prince Albert, 1:148 752

sheet Mossel Bay, and from mapping by Rossouw, P.J., & Blignaut, J.J.G. (1939-40),

Haughton, S.H., & Frommurze, H.F. (1930-3), Du Plessis, P.G. (1944-4), Marlow, A.G.

(1973-74), Potgieter, C.T. (1946-47), Krynauw, J.R. (1975), and Gresse, P.G. (1974), and

revised in part by Toerien, D.K. (1973-77); map 3322, Council for Geoscience, Pretoria.

Umvoto Africa (PTY) Ltd (2005). Deep artesian groundwater for Oudtshoorn Municipal

Supply Phase D Target generation & borehole/wellfield siting using structural geology and

geophysical methods. Water Research Commission (WRC), Report No. 1254/1/105.ISBN

No. 1-77005-239-9, 240 pp.

Wells, D.L., & Coppersmith, K.J. (1994). New empirical relationships among magnitude,

rupture length, rupture width, rupture area, and surface displacement, Bulletin of the

Seismological Society of America 84(4) 974–1002.

Wesnousky, S.G. (2008). Displacement and geometrical characteristics of earthquake

surface ruptures: Issues and implications for seismic-hazard analysis and the process of

earthquake rupture, Bulletin of the Seismological Society of America 98(4), 1609–1632.


475

Table 4.12. Data Evaluation Table 8.4.2. Agulhas Fracture Zone Fault Source (AFZ)



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Argus et al. Geologically Current Motion of 56 Plates Relative to the No-Net-Rotation Reference Frame

2011 Slip rate

• Defines the Nubia-Lwandle (NU-LW) plate boundary. Slip rate on AFZ would be much lower than rate of deformation across the NB- LW boundary.

Q3/R2

(limiting rate)

Ben-Avraham Neotectonic Activity Offshore Southeast Africa and Its Implications


• Regional study showing evidence for neotectonic activity (faulting and recent volcanism) in the offshore region.

• Faults offset Pliocene units on seismic line across portion of Agulhas Plateau (Fig. 2).

• Agulhas fracture zone: passive margin for over 100 Ma; surprised to see evidence locally for reactivation (Fig. 4, quality of profile is poor and there is minimal penetration); some lines show evidence for no recent activity; reactivation is assumed to have triggered large slumps (Dingle & Robson, 1985; Dingle et al. 1987). It is assumed that the Diaz Ridge segment (which includes the seismic line shown on Fig. 4 and the large Agulhas slump, is interpreted to have been reactivated. However, the article is not clear about which segments show evidence for reactivation.

• Observations (this study): apparent seafloor scarp and anomalous features in Fig. 4 may be erosional; recent higher-quality seismic profile data shows the inferred large Agulhas ‘slump’ is not due to mass movement, but rather is related to erosional processes on the slope (Uenzelmann-Neben & Huhn, 2009).

Fault location and geometry

• Fault showing possible evidence for reactivation (seafloor scarp) is at the base of the scarp.

Q2/R3 Q3/R3

Ben-Avraham et al.

Neotectonic Activity on Continental Fragments in the Southwest Indian Ocean: Agulhas Plateau and Mozambique Ridge


• Regional study showing evidence for recent volcanism in the offshore region.

Q3/R2

Ben-Avraham et al.

Structure and Tectonics of the Agulhas-Falkland Fracture Zone


• The Agulhas transform zone was active from 130 Ma to 65 Ma.

Fault geometry

• The 1,200 km long Agulhas-Falkland Fracture Zone is divided into four distinct sections off the South African coast; discussion of different sections does not include much discussion of structural elements or evidence for

Q4/R3 Q4/R4


476



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



reactivation.

• Location of the fault as shown on Fig. 1 appears very consistent with inferred northern limit of oceanic crust based on magnetic anomalies

Bird et al. Plate Tectonics and Earthquake Potential of Spreading Ridges and Oceanic Transform Faults

2002 Mmax

• M 7+ earthquakes on ridge transform faults.

Q4/R4

Boettcher & McGuire

Scaling Relations for Seismic Cycles on Mid-Ocean Ridge Transform Faults

2009 Mmax

• Magnitudes of the largest earthquakes on mid-ocean ridge transform faults

• transform motion is largely aseismic,

• magnitudes of the largest events are small (6 ≤ Mw ≤ 7.1) compared to large transform areas.

Q4/R4

Bufe Stress Distribution Along the Fairweather-Queen Charlotte Transform Fault System

2005 Mmax

• M 8.1 Queen Charlotte Island earthquake (1946).

Q3/R4

De Mets et al. Geologically Current Plate Motions

2010 Slip rate

• Defines the Nubia-Lwandle (NU-LW) plate boundary.

• Rate across the Southwest Indian Ridge plate pairs is 0.4 mm/yr.

• If boundary lies along Andrew Bain fracture zone, the indicated motion is ~ 2 mm/yr right shear with some extension.

• However, in the interpretation of magnetic anomalies by Patriat et al. (2008), there is no movement between Nubia and Lwandle in the past 11 Ma.

Q4/R2

(limiting rate)

Hanson et al. Style and Rate of Quaternary Deformation of the Hosgri Fault Zone, Offshore South-Central California

2004 Fault geometry

• Methodology for assessing style of faulting based on different assumtions and the resulting H:V ratio.

Q3/R3

Hanson et al. Thyspunt Geological Investigations—Marine Terrace Studies

2012a Recurrence

• Provides discussion of marine terrace data and results of cosmogenic dating that constrain uplift rates onshore.

Q4/R4

Hartnady Earthquake Hazard in Africa: Perspectives on the Nubia–Somalia Boundary

2002 Recurrence (relative to plate boundary rate)

• Maps alternative boundaries between the Nubian and Lwandle Plates.

Q3/R1


477



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Hartnady & le Roex

Southern Ocean Hotspot Tracks and the Cenozoic Absolute Motion of the African, Antarctic, and South American Plates


• The Agulhas transform zone was active from 130 Ma to 65 Ma.

Q3/R3

Ishii et al. Mw 8.6 Sumatran earthquake of 11 April 2012: Rare Seaward Expression of Oblique Subduction

2013 Mmax

• M 8.6 Sumatran earthquake (2012) was related to the nearby oblique subduction (not a good analogue for the AFZ).

Q4/R2

Lamontagne Significant Canadian Earthquakes of the Period 1600-2006

2008 Mmax

• M 8.1 Queen Charlotte Island earthquake (1946).

Q4/R4

LeMaux et al. Location of the Nubia-Somalia Boundary Along the Southwest Indian Ridge

2002 Recurrence

• The main locus of deformation between the Nubia and Somalia Plates near the Southwest Indian Ridge over the past 11 Myr can be no wider than a few hundred kilometers, from ~100 km west of the Du Toit fracture zone to ~50 km east of the Andrew Bain fracture zone complex, a closely spaced set of fracture zones along which deformation is most likely concentrated. The Andrew Bain fracture zone complex is only ~100 km wide. The displacement along this boundary over the past 11 Myr is 23 km ± 6 km (95% confidence limits), indicating a displacement rate of 2 mm/yr, much slower than typical rates of seafloor spreading and subduction.

Q3/R2

(limiting rate)

Martin & Hartnady

Plate Tectonic Development of the Southwest Indian Ocean: A Revised Reconstruction of East Antarctica and Africa


• Tectonic activity at the southern continental margin of Africa ceased 100 Ma.

Q2/R2

Nyblade & Robinson

The African Superswell 1994 Style of faulting

• The African Superswell is a zone of elevated topography due possibly in part to ongoing heating of the lithosphere.

Q4/R3

Okal & Stein The 1942 Southwest Indian Ridge Earthquake: Largest Ever Recorded on an Oceanic Transform

1987 Mmax

• Seismic moment is 1.3 x 1028 dyn/cm, rupture 130 km long; MS = 8.1 ± 0.4 (mb = 7.7; MS = 8.1; Mw = 8.0).

Q4//R4

Parsiegla et al. Deep Crustal Structure of The Sheared South African Continental Margin: First Results of the Agulhas-Karoo Geoscience Transect


• Indicates that there is evidence for neotectonic and possible triggered volcanic activity in the Agulhas Passage.

• Suggests faults associated with the Diaz Ridge segment may have been reactivated—possibly related to thermal

Q2/R2 Q4/R3 Q2/R3

Q5/R5


478



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



uplift of southern Africa.

Fault geometry

• AFFZ is 52 km wide (p. 402).

Style of faulting

• Younger tectonic motion may not be vertical; it may have been linked to vertical motion on the African Superswell (p. 404); AFFZ may have acted as a zone of crustal weakness along which the uplift process was accommodated.


• Crust thins from 30 km to 7 km thick across AFFZ (p. 402); Fig. 10 is good figure showing interpretation of sheared margin along AFFZ.

Parsiegla et al. The Agulhas Plateau: Structure and Evolution of a Large Igneous Province


• The Agulhas Plateau formed as a large igneous province ~100 Ma. The formation was accompanied by normal faulting.

Q3/R2

Parsiegla et al. Southern African Continental Margin: Dynamic Processes of a Transform Margin


• Cross-references to Ben-Avraham (1995), Ben-Avraham et al. (1995), and Parsiegla (2007) for evidence for neotectonic activity.

Fault geometry

• AFFZ is embedded in a 50 km wide transitional zone between continental and oceanic crust (Fig. 6).

Style of faulting

• Transtensional shear motion ~136 Ma: possible later period of transpressional deformation along AFFZ, or—more likely—thermal uplift of a spreading ridge to the south (explanation for Diaz Marginal Ridge).

Q3/R1 Q4/R3 Q3/R3

Reznikov et al. Structure of the Transkei Basin and Natal Valley, Southwest Indian Ocean, from Seismic Reflection and Potential Field Data


• Evidence for seismicity and neotectonic activity in the southern Natal Valley and northern Transkei Basin that may be related to the diffuse boundary between the Nubia and Somalia Plates.

Q3/R2

Satriano et al. The 2012 Mw 8.6 Sumatra Earthquake: Evidence of Westward Sequential Seismic Ruptures Associated to the Reactivation of a N-S Ocean Fabric

2012 Mmax

• M 8.6 Sumatran earthquake (2012) occurred in a zone of diffuse deformation associated with an obliquely convergent plate boundary.

• Evaluated but judged not a good analogue for AFZ.

Q4/R2


479



3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Stamps et al. Lithospheric Buoyancy Forces in Africa from a Thin Sheet Approach

2010 Recurrence

• Recent analysis of geodetic data and earthquake slip vectors in East Africa shows that

– Present-day Nubia-Somalia motion is consistent with the ~3 Myr average.

– The kinematics of the plate boundary zone is best described with a model that includes three minor sub-plates defined using the distribution of seismicity (Victoria, Rovuma, and Lwandle).

• Extension is directed ~E-W along the rift, with rates decreasing from 6–7 mm/yr in the Main Ethiopian Rift and 3-4 mm/yr in the central EAR, to <1 mm/yr south of Mozambique.

• The Nubian Plate behaves rigidly at the current precision level of the GPS measurements.

Q4/R2

(limiting rate)

Uenzelmann-Neben & Huhn

Sedimentary Deposits on the Southern South African Continental Margin: Slumping Versus Non-deposition OR Erosion by Oceanic Currents?


• Faults offset Pliocene units (Fig. 7).

• Evidence is presented to disprove the size and extent of the Agulhas Slump as proposed by Dingle (1977): erosional processes rather than mass movement have given rise to the bathymetric features. The Agulhas slump was indirectly cited by Ben-Avraham (1995) as possible evidence of strong ground shaking (possibly associated with the AFZ).

Fault geometry

• Width of zone of faults; location of northwesternmost fault trace; dip of mapped faults is vertical to steeply dipping (Figs. 2 and 7).

Slip rate

• Minimum apparent vertical stratigraphic offset of inferred Pliocene horizon is 600–1,800 m across zone of faults (excepting possible fault at base of continental slope). It is not clear from the published figures (due to extreme vertical exaggeration) how much of the apparent vertical offset is due to initial drape on a sloping sea bottom.

Q5/R4 Q5/R5 Q3/R4






480

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Ben-Avraham, Z., Hartnady, C.J.H., & Kitchin, K.A. (1997). Structure and tectonics of the


Ben-Avraham, Z., Hartnady, C.J.H., & le Roex, A.P. (1995). Neotectonic activity on

continental fragments in the southwest Indian Ocean: Agulhas Plateau and Mozambique

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DeMets, C., Gordon, R.G., & Argus, D.F. (2010). Geologically current plate motions,


Dingle, R.V. (1977). The anatomy of a large submarine slump on a sheared continental

margin (SE Africa), Journal of the Geological Society of London 134, 293-310.

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481

Fincham, M.J., and 17 others (1987). Deep-sea sedimentary environments around southern

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margin off East London, SE Africa (SW Indian Ocean), Marine Geology 67, 37 54.

Hanson, K., Glaser, L., Coppersmith, R., Roberts, D.L., Claassen, D., & Black, D.E. (2012a).

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Hanson, K.L., Lettis, W.R., McLaren, M.K., Savage, W.U., & Hall, N.T. (2004). Style and rate

of Quaternary deformation of the Hosgri Fault Zone, offshore south-central California. In:

Evolution of Sedimentary Basins / Offshore Oil and Gas Investigations—Santa Maria

Province, M.A. Keller (ed.), U.S. Geological Survey Bulletin 1995, chap. BB, 33 pp.

Hartnady, C.J.H. (2002). Earthquake hazard in Africa: Perspectives on the Nubia-Somalia

boundary, South African Journal of Science 98, 425-428.

Hartnady, C.J.H., & le Roex, A.P. (1985), Southern Ocean hotspot tracks and the Cenozoic

absolute motion of the African, Antarctic, and South American plates, Earth and Planetary

Science Letters 75, 245-257.





Lemaux, J., Gordon, R.G., & Royer, J.Y. (2002). Location of the Nubia-Somalia boundary

along the Southwest Indian Ridge, Geology 30(4), 339-342.

Martin, A.K., & Hartnady, C.J.H. (1986). Plate tectonic development of the southwest Indian

Ocean: A revised reconstruction of East Antarctica and Africa, Journal of Geophysical

Research 91(B5), 4767-4786.



482

Nyblade, A.A. & Robinson, S.W. (1994). The African superswell, Geophysical Research

Letters 21, 765-768.

Okal, E., & Stein, S. (1987). The1942 Southwest Indian Ridge earthquake: Largest ever

recorded on an oceanic transform, Geophysical Research Letters 14, 147-150.

Parsiegla, N., Gohl, K., & Uenzelmann-Neben, G. (2007). Deep crustal structure of the

sheared South African continental margin: First results of the Agulhas-Karoo Geoscience

Transect, South African Journal of Geology 110, 393-406.

Parsiegla, N., Gohl, K., & Uenzelmann-Neben, G. (2008). The Agulhas Plateau: Structure

and evolution of a large igneous province, Geophysical Journal International 174, 336-350.

Parsiegla, N., Stankiewicz, J., Gohl, K., Ryberg, T., & Uenzelmann-Neben, G. (2009).


Geochemistry, Geophysics, Geosystems 10(3), 20 pp., doi:10.1029/2008GC002196.

Patriat, P., Sloan, H., & Sauter, D. (2008). From slow to ultraslow: A previously undetected

event at the Southwest Indian Ridge at ca. 24 Ma, Geology 36, 207-210.

Reznikov, M., Ben-Avraham, Z., Hartnady, C., & Niemi, T.M. (2005). Structure of the

Transkei basin and Natal valley, Southwest Indian Ocean, from seismic reflection and

potential field data, Tectonophysics 397, 127-141.


earthquake: Evidence of westward sequential seismic ruptures associated to the reactivation

of a N-S ocean fabric, Geophysical Research Letters 39(L15302), doi:10.1029/

2012GL052387.

Stamps, D.S., Flesch, L.M., & Calais, E. (2010). Lithospheric buoyancy forces in Africa from

a thin sheet approach, International Journal of Earth Science 99, 1525-1533.

Uenzelmann-Neben, G., & Huhn, K. (2009). Sedimentary deposits on the southern South

African continental margin: Slumping versus non-deposition or erosion by oceanic currents?

Marine Geology 266, 65-79.

483


Table 4.13. Data Evaluation Table 8.4.3. Gamtoos Fault Source (GAM)



3)



p(S) Fault

Geometry


Rupture Geometry



Anderson et al. A New, Integrated Multidisciplinary Geodynamic / Geophysical Approach to Ground Water Exploration Around the South African Coastline

1996 Fault geometry

• Mapped the Gamtoos fault onshore and in the nearshore

Q3/R3



• Seismic profile on Fig. 2 shows Gamtoos Fault dying out in Tertiary section, overlain by unfaulted upper unit.

Fault geometry

• Seismic data suggest that the Gamtoos is a single discrete fault plane, but it is possible that it is a segmented fault zone comprising the Gamtoos and Elandsberg Faults (like what is observed onshore).

Q3/R4 Q4/R4

Broad et al. Offshore Mesozoic Basins 2006 Seismogenic probability

• Seismic profile on Fig. 4c shows unfaulted drift sediments and Tertiary section overlying Gamtoos Fault.

• Fig. 7 (southern end of offshore fault) shows unfaulted Tertiary above Gamtoos Fault.

Fault geometry

• 60 km long fault onshore, 90 km offshore (Fig. 5).

Style of faulting

• Listric geometry (Fig. 7).


• Fig. 7 shows fault down to depth of at least 10 km.

Q3/R4 Q2/R3 Q2/R1 Q4/R3

Davies Pleistocene Shorelines in the Western Cape and South-West Africa


• Marine deposits on the hanging wall block along the Gamtoos River are at elevations of 18 m amsl.

• Important data set used in regional marine terrace (correlations see Hanson et al., 2012a).

Q3/R4

De Beer Investigation into Evidence for Neotectonic Deformation Within Onland Neogene to Quaternary Deposits Between Alexander Bay and Port Elizabeth—South Coast Report


• Possible trace of Gamtoos Fault does not show any geomorphic expression based on inspection of aerial photographs and 10 m DEM.

Q2/R3


484



3)



p(S) Fault

Geometry


Rupture Geometry



De Wet Bathymetry of the South African Continental Shelf


• Bathymetric data that can be used to evaluate extent of seafloor scarp along fault zone and evidence for post-LGM rupture of seafloor.


• No evidence for seafloor scarp beyond 100 m isobath suggests that the scarps observed in seismic data (Roux, 2011) may be erosional. No evidence in bathymetry for post-LGM faulting.

Q4/R2 Q4/R5

Du Toit Mesozoic Geology of the Agulhas Bank, South Africa

1976 Fault geometry

• Offshore fault trace (Plate 1 “Horizon D”) length 100 km.

Q4/R5

Dunajko Mid- to Late Quaternary Evolution of the Wilderness Barrier Dunes, South Africa

2011 Recurrence/recency & slip rate/RI

• Analogue for ages of inactive Gamtoos dune fields.

Q5/R3

Goedhardt Potential Onshore and Offshore Geological Hazards for the Thyspunt Nuclear Site, Eastern Cape, South Africa: A Review of the Latest Airborne and Marine Geophysical Data and Their Impact on the Existing Geological Model for the Site Vicinity Area


• Refers to review of Petroleum Agency data by J. Roux for possible scarps at seafloor; similar to interpretation of lines presented by Davids (Roux, 2011).

• No data for the reactivation of the Elandsberg Fault.

• Author reviewed publications and unpublished data for this project, as outlined in this table, but this publication is not heavily relied upon for this fault source.

Q2/R2

Goedhart et al. Groundwater Targeting in the Algoa Bay Region, from Humansdorp to Alexandria, Eastern Cape, South Africa

2004 Fault geometry

• Mapped the Gamtoos fault onshore and in the nearshore.

Q3/R3


2012a Seismogenic probability

• Compilation of marine terrace data does not show variations of higher terraces (~18 m and ~30 m terraces inferred to be probably Pliocene or earliest Pleistocene for the 18 m terrace) to across the Gamtoos Fault, indicating no recent activity within the resolution of the data.

• No obvious geomorphic expression of recent faulting observed in aerial photographs and GoogleEarth imagery.

Q4/R5



• Analogue based on similar orientation and deformational history.

Geometry/style of faulting

• Analogue for expected style of faulting in contemporary tectonic regime.

Q4/R1 Q3/R4 Q4/R5


485



3)



p(S) Fault

Geometry


Rupture Geometry



Mmax

• Kango Fault as analogue for Mchar: this report provides summary of geometric, structural, and behavioural data used to develop the maximum magnitude distribution for the Kango Fault.

McMillan et al. Late Mesozoic Sedimentary Basins off the South Coast of South Africa


• Offset of Tertiary sediments indicates southern end of Gamtoos Fault may have been active in mid-Tertiary, but faulting does not extend through entire section to seafloor (Fig. 17, based on Malan et al., 1990).

• South of southward bend in fault, there is no indication of offset of the Upper Cretaceous 15At1 unconformity and overlying Tertiary sediments (Profile H-H′, Fig. 18).

Style of faulting

• Normal, based on the fault being one of the reactivated Cape Fold Belt structures, and based on offset of Mesozoic sediments.


• Offshore, the fault is traced to a depth of at least 12 km.

Q4/R4 Q3/R3 Q4/R5

Nolte Structure and Tectonostratigraphy of the Gamtoos Belt Between Tweewaters and Classen Point, Eastern Cape Provence, R.S.A.


• Based on cross-cutting relations, the Elandsberg Fault has not been active as recently as the other faults in the horst.

• Tertiary gravels lie on top of some of the cross faults.

• Near the coast, Quaternary deposits obscure the trace of the Gamtoos Fault.

Fault geometry

• Detailed map of onshore fault; length of onshore fault is 75 km.

• Straight trend of onshore fault indicates a steep dip.

Q2/R2 Q4/R3

Paton Influence of Crustal Heterogeneity on Normal Fault Dimensions and Evolution: Southern South Africa Extension System


• Inactive—The fault is not exposed at the coast on account of Quaternary deposition, and there is no bathymetric expression of the fault.

Fault geometry

• Fault is 170 km long and if linked with the Kango and Bavianskloof Faults, the Gamtoos Fault is part of a 480 km long system. (Note: Other researchers prefer to link the Coega rather than the Gamtoos to the Kango and Baviaanskloof Faults [e.g., Goedhard, 2004]).

• Cross-sectional geometry of the fault plane demonstrates that the fault is continuous, linear, and nonsegmented (Fig. 8).

Q2/R2 Q3/R2 Q2/R3 Q3/R2


486



3)



p(S) Fault

Geometry


Rupture Geometry



• Dip 42.5°.

• Interpretation does not show Gamtoos anticline in hanging wall; possible alternative interpretation of a more steeply dipping fault is suggested by other researchers (e.g., Malan et al., 1990).

Mmax

• Indirect information regarding segmentation—No evidence at the resolution of data of fault segmentation, isolated depocentres, or intrabasin faults, progressively coalescing during the syn-rift interval.

Style of faulting

• Reactivated Cape Fold Belt structure, negative inversion.

• Normal, based on offset of Tertiary and older sediments in marine seismic profiles.

Paton & Underhill

Role of Crustal Anisotropy in Modifying the Structural and Sedimentological Evolution of Extensional Basins: The Gamtoos Basin, South Africa

2004 Fault geometry

• No evidence at the resolution of data of fault segmentation, isolated depocentres, or intrabasin faults, progressively coalescing during the syn-rift interval.

• The 90° bend in the fault is inherited from underlying strata.

• The fold along the southern part of the fault is a consequence of the accommodation of extension by the unusual plan-view geometry of the fault (not due to the complex interplay of compression and extension, as suggested by previous workers).

Q5/R4

Roux Offshore Geophysical Data 2011 Seismogenic probability

• Seafloor scarps ranging from 34 to 52 m along the Gamtoos and other faults in St. Francis Bay.

• 22At1 unconformity appears to be eroded on footwall, and there is extensive erosion of Tertiary section on hanging wall; the scarp could thus be an erosionally faultline scarp.

Fault geometry

• Offshore segment with seafloor scarp is approximately 50 km long.

Rupture geometry

• If seafloor scarp is tectonic, then offset is normal.

Q3/R3

Based on interpretation of seismic data collected to image deep part of section.

Q4/R3

Q2R3

Shone et al. Pre-Cape Rocks of the Gamtoos Area—A Complex Tectonostratigraphic Package Preserved as a Horst Block


• Based on cross-cutting relations, the Elandsberg Fault has no evidence for recent reactivation.

Rupture geometry

• Map of Elandsberg Fault.

Q4/R1 Q3/R2


487



3)



p(S) Fault

Geometry


Rupture Geometry



Stankiewicz et al.


2007 Rupture geometry

• Listric geometry onshore.


• Onshore seismic refraction shows the fault to at least 15 km depth.

Dip

Q4/R3

Q4/R3

Thomson Role of Continental Break-Up, Mantle Plume Development and Fault Reactivation in the Evolution of the Gamtoos Basin, South Africa


• Reactivation of Cape Fold Belt thrusts as extensional structures during breakup of Gondwana.

• Dextral movement on Agulhas-Falkland Fracture Zone during Valanginian (Early Cretaceous) resulted in reactivations of structures with extensional, compressional, and strike-slip senses of movement.

• Post-rift thermal subsidence phase with passive infill and onlap of the topography.

• Uplift of the basin resulting from the westward migration of the Falkland Plateau and Natal Valley spreading centre past the basin, resulting in nondepositional hiatus and local channeling before erosion in the Cenomanian.

• Following renewed subsidence, the basin experienced uplift during the Palaeocene and Eocene, the cause of which is problematic but is contemporaneous with igneous intrusion in southern Africa.

• Figs. 6 and 7 show unfaulted sections above 15At1 and 14At1 marker horizons (both Cretaceous), respectively. The locations of the seismic profiles are not given.

Fault geometry

• Listric geometry in some offshore profiles.

Q4/R3 Q4/R2

Zhang The Evolution of the Gamtoos River Floodplain, South Africa


• River terraces from rise from 30 to 90 m.

Q2/R1

1 Sorted by the criteria for identifying the seismic source: probability of activity, source/fault geometry, recurrence, Mmax, or future earthquake characteristics (rupture geometry, style of faulting, and

seismogenic thickness).

2 Quality refers to the degree to which these particular data relate to and provide insights to the SSC model and can be used in its development. Quality (Q1 = low; Q5 = high) 3 Reliance is the degree to which the data provide direct support and justification for particular elements/parameters of the SSC Mode. Reliance (R1 = low, U5 = high)

488



References

Anderson, N.J.B., IIIenberger, W.K., Walton, D.G., & Hambleton-Jones, B.B. (1996). A New,

Integrated Multidisciplinary Geodynamic I Geophysical Approach to Ground Water

Exploration Around the South African Coastline, Unpublished Final Draft (07 June 1996,

Volumes 1 & and 10 Sept 1996, Volumes 1 & 2), Report No. GEA 1096, Earth and

Environmental Technology Department, Atomic Energy Corporation of South Africa, 113 pp.

(+ maps in Vol. 2).




Balkema, Rotterdam.

Broad, D.S., Jungslager, E.H.A., McLachlan, I.R. & Roux, J. (2006). Offshore Mesozoic


(eds.), Geological Society of South Africa, Johannesburg, and the Council for Geoscience,

Pretoria, pp. 553-571.


(Part 2), Annals of the Natal Museum 21 (2), 225-279.



Report, Council for Geoscience Report No. 2005-0180, 187 pp.

de Wet, W.M. (2012). Bathymetry of the South African continental shelf, MSc Thesis,

University of Cape Town.

Dunajko, A.C. (2011). Mid- to Late Quaternary evolution of the Wilderness barrier dunes,

South Africa, doctoral thesis, University of Sheffield, Department of Geography, 254 pp.





489


Reactivation Along the Ceres-Kango–Baviaanskloof-Coega Fault System in the Southern

and Eastern Cape, South Africa, CGS Report No. 2004-0189, ESKOM NSIP-SHA-

013852#P1-153, 129 pp.


Nuclear Site, Eastern Cape, South Africa: A Review of the Latest Airborne and Marine

Geophysical Data and Their Impact on the Existing Geological Model for the Site Vicinity

Area, CGS Report No. 2007-0274, 85 pp. Revision of 2007 report.

Goedhart, M.L., Small, G.W., & Hulley, V. (2004). Groundwater Targeting in the Algoa Bay

Region, from Humansdorp to Alexandria, Eastern Cape, South Africa, Report No. 2004-1061,

Council for Geoscience, Pretoria, , 261 pp.

Hanson, K., Glaser, L., Coppersmith, R., Roberts, D.L., Claassen, D. & Black, D.E. (2012a).

Thyspunt Geological Investigations—Marine Terrace Studies, Council for Geoscience

Report No. 2012-0034, Rev. 0, 126 pp.

Hanson, K., Slack, C. & Coppersmith, R. (2012b). Thyspunt Geological Investigations—

Kango Fault Study, Council for Geoscience Report Number 2012-0035, Rev. 0, 126 pp.

Malan, J.A. (1990). The stratigraphy and sedimentology of the Bredasdorp Group, southern

Cape Province, South Africa, unpublished MSc Thesis, University of Cape Town, 197 pp.

McMillan, I.K., Brink, G.I., Broad, D.S. & Maier, J.J. (1997). Late Mesozoic sedimentary

basins off the south coast of South Africa. In: African Basins, R.C. Selley (ed.), vol. 3 in

Sedimentary Basins of the World series, pp. 319-376, Elsevier, Amsterdam.

Nolte, C.C. (1990). Structure and Tectonostratigraphy of the Gamtoos Belt Between

Tweewaters and Classen Point, Eastern Cape Province, R.S.A., MSc Thesis, University of

Port Elizabeth, 267 pp.


evolution: Southern South Africa extensional system, Journal of Structural Geology 28 (5),

868-886, doi:10.1016/j.jsg.2006.01.006.



490

Paton, D.A. & Underhill, J.R. (2004). Role of crustal anisotropy in modifying the structural

and sedimentological evolution of extensional basins: The Gamtoos Basin, South Africa,

Basin Research 16, 339-359.



Shone, R.W., Nolte, C.C. & Booth, P.W.K. (1990). Pre-Cape rocks of the Gamtoos area—A


Geology 93 (4), 616-621.

Stankiewicz, J., Ryberg, T., Schulze, A., Lindeque, A., Weber, M.H. & de Wit, M.J., (2007).



Thomson, K. (1999). Role of continental break-up, mantle plume development and fault

reactivation in the evolution of the Gamtoos Basin, South Africa, Marine and Petroleum

Geology 16, 409-429.

Zhang, P. (1995). The evolution of the Gamtoos River floodplain, South Africa, unpublished

MSc Thesis, University of Port Elizabeth, 94 pp.


491

Table 4.14. Data EvaluationTable 8.4.4. Plettenberg Fault Source (PLET)





p(S) Fault

Geometry


Rupture Geometry



Bate & Malan Tectonostratigraphic Analysis of the Algoa, Gamtoos, and Pletmos Basins, Offshore South Africa

1992 Fault geometry

• Downthrow towards the south or southwest.

Style of faulting

• Reactivated Cape Fold Belt fault (normal faulting).

Q4/R4 Q3/R3

Booth & Shone Pre-Cape Table Mountain Group Contact West of Port Elizabeth


• Reactivated Cape Fold Belt fault (normal faulting).

Q3/R3

Broad et al. Offshore Mesozoic Basins 2006 Style of faulting

• Reactivated Cape Fold Belt fault.

• Normal faulting based on offset of Tertiary and older sediments.

Q4/R3

Brown et al. Sequence Stratigraphy in Offshore South African Divergent Basins


• Fault trace is not extended to seafloor (Profile L-L′).

Fault geometry


Style of faulting



Q3/R4 Q4/ Q4/R3

Colletini & Sibson

Normal Faults, Normal Friction?


• Generic distribution of normal fault dips (30°–65°).

Q4/R2 Q4/R3

De Wet Bathymetry of the South African Continental Shelf


• Bathymetric data that can be used to evaluate extent of seafloor scarp along fault zone and evidence for post-LGM rupture of seafloor.


• No evidence for seafloor scarp beyond 100 m isobath suggests that the scarps observed in seismic data (Roux, 2011) may be erosional. No evidence in bathymetry for post-LGM faulting.

Q4/R4 Q4/R5

Du Toit Mesozoic Geology of the Agulhas Bank, South


• Offshore fault trace (Plate 1 “Horizon D”) length

Q4/R4


492





p(S) Fault

Geometry


Rupture Geometry



Africa 105 km.


Investigations—Marine

Terrace Studies


• Most authors do not extend the Plettenberg Fault onshore. Paton (2006) suggests that it might extend onshore to bound an onshore Mesozoic basin. If the Plettenberg Fault extends onshore, shore-parallel profiles of marine terrace data do not show variations in elevation along Mossel Bay where the Plettenberg Fault may come ashore, indicating no late Pliocene to Quaternary uplift within a resolution of approximately 5 m.

Q4/R1

Jackson & White

Normal Faulting in the Upper Continental Crust: Observations From Regions of Active Extension

1989 Fault geometry

• Generic distribution of normal fault dips (30°–60°).

Q4/R3

McMillan et al. Late Mesozoic Sedimentary Basins off the South Coast of South Africa


• The 6At1 unconformity marks the end of substantial normal motion on the Plettenberg Fault.

Seismic source or fault geometry


Style of faulting



Q4/R2 Q4/R5 Q4/R3

Paton Influence of Crustal Heterogeneity on Normal Fault Dimensions and Evolution: Southern South Africa Extension System


• No bathymetric expression of fault.

Fault geometry

• Fault may come ashore in Plettenberg Bay and be associated with Mesozoic sediments.

• Observed minimum length 160 km.

• 50°–65° planar dip (Figure 7).

• Evidence for rapid localisation of displacement on a major basin-bounding fault is hypothesised to be a consequence of the pre-existing fabric (p. 864).

Mmax

• Evidence for segmentation: Despite change in

Q2/R2 Q4/R5 Q3/R3 Q3/R3 Q4/R5

(minimum)


493





p(S) Fault

Geometry


Rupture Geometry



trend of the fault from WNW–ESE to N–S orientation, the cross-sectional geometry of the fault remains the same along the entire length. Interpolation of the fault plane to form a 3-D surface produces a fault plane that is a discrete, approximately continuous, smooth surface without steps in trend. There is no evidence of abandoned fault tips in either the hanging wall or footwall, or an en-echelon configuration, and therefore, the fault does not comprise a nonlinear fault segment.

Style of faulting




• Fault is imaged to at least 13 km.

Paton et al. Applicability of Thin or Thick Skinned Structural Models in a Region of Multiple Inversion Episodes; Southern South Africa

2006 Seismogenic thickness

• Fault is imaged to at least 12 km.

Q4/R5

Roux TNP SSHAC 3 Workshop 1


• Evidence for no scarp on northern two example seismic lines (A and B); two southern lines (E and F) show possible evidence for unfaulted sediments below the 22At1 unconformity (i.e., an inferred wedge of Cretaceous sediments at a paleoshelf break?).

• Up to 22 m vertical displacement (assuming seafloor scarp is due to tectonic faulting) on the Plettenberg Fault.

Seismic source or fault geometry

• Length of fault with apparent seafloor scarps ~35 km.

Style of faulting

• Assuming that the seafloor scarp is tectonic—suggests down-to-the south movement (normal faulting).

Q3/R4 Q4/R4 Q2/R3


494

1 Sorted by the criteria for identifying the seismic source: probability of activity, source/fault geometry, recurrence, Mmax, or future earthquake characteristics (rupture geometry, style of faulting, and

seismogenic thickness).





495

References


Pletmos Basins, offshore South Africa. In: M.J. de Wit & I.G.D. Ransome (eds.), Inversion

Tectonics of the Cape Fold Belt, Karoo and Cretaceous Basins of Southern Africa, pp. 61-73,

Balkema, Rotterdam.

Booth, P.W.K., & Shone, R.W. (1992). The pre-Cape—Table Mountain Group contact west

of Port Elizabeth, South African Journal of Geology 95(1/2), 34-39.

Broad, D.S., Jungslager, E.H.A., McLachlan, I.R., & Roux, J. (2006). Offshore Mesozoic


(eds.), pp. 553-572, Geological Society of South Africa, Johannesburg / Council for


Brown, L.F., Benson, J.M., Brink, G.J., Doherty, S., Jollands, A., Jungslager, E.H.A., Keenan,

J.H.G., Muntingh, A. & van Wyk, N.J.S. (1995). Sequence Stratigraphy in Offshore South

African Divergent Basins: An Atlas on Exploration for Cretaceous Lowstand Traps by Soekor

(Pty) Ltd., AAPG Studies in Geology #41, 184 pp.


de Wet, W.M. (2012). Bathymetry of the South African continental shelf. MSc Thesis,

University of Cape Town.



Hanson, K., Glaser, L., Coppersmith, R., Roberts, D.L., Claassen, D. & Black, D.E. (2012a).



Jackson, J.A. & White, N.J. (1989). Normal faulting in the upper continental crust:

Observation from regions of active extension, Journal of Structural Geology 11(1/2), 15-36.



496

McMillan, I.K., Brink, G.I., Broad, D.S. & Maier, J.J. (1997). Late Mesozoic sedimentary

basins off the south coast of South Africa. In: R.C. Selley (ed.), African Basins, vol. 3 in

Sedimentary Basins of the World series, pp. 319-376, Elsevier, Amsterdam.

Paton, D.A., Macdonald, D.I.M. & Underhill, J.R. (2006). Applicability of thin or thick skinned

structural models in a region of multiple inversion episodes: Southern South Africa, Journal

of Structural Geology 28(11), 1933-1947.


evolution: Southern South Africa extensional system, Journal of Structural Geology 28(5),

868-886, doi:10.1016/j.jsg.2006.01.006.




497

Table 4.15. Data Evaluation Table 8.4.5. Worcester Fault Source (WOR)

Author Title Year Relevant Information

1


3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry




Geochronology, Southern

Africa Fault Corridor

Investigation

2012a Seismogenic probability and Recurrence

• Estimates of rock uplift inferred from cosmogenic nuclide analysis of stream sediments, in combination with similar data from Scharf et al. (2011), suggest that there has been no measurable differential uplift of region encompassing Worcester Fault and projected trend of the fault to coastline.

Q4/R2 Q4/R2

(Data suggest no significant differential uplift of entire Eastern Cape region.)

De Beer Investigation into Evidence

for Neotectonic

Deformation Within Onland

Neogene Quaternary

Deposits Between

Alexander Bay and Port

Elizabeth—South Coast

Report


• Possible neotectonic faulting (Figure 42d shows thick scree (unfaulted) over fault.

• Nowhere could the author demonstrate offset of Pliocene or Pleistocene deposits.

Fault geometry

• Figure 39 is map of extent of Worcester Fault.

• Possibly links up offshore with the Plettenberg Fault (mentioned in text, but continuous fault not shown on Figure 39).

Recurrence

• Road cut east of Zuurbraak (Figure 41) shows evidence for possible neotectonic reactivation of Worcester Fault; two faults, each showing vertical displacement of ~0.5 m, displace channel gravel (unit A) inset into Cretaceous Kirkwood Formation.

• Overlying subhorizontal unconformity between units A and B (terrace gravel deposit) is not deformed.

• Estimated age of most recent faulting is >1.3 Ma based on amount of time estimated for the Tradouw River to incise 20 m below unconformity between units A and B.

Style of faulting

• Normal reactivation of Cape Fold Belt thrust.

• Steep normal fault with a southerly downthrow.

Q3/R4 Q4/R4 Q4/R5

(Lack of evidence for offset of Pliocene and Pleistocene deposits is used to constrain low rate of slip if active.)

Q4/R3

Du Toit Mesozoic Geology of the

Agulhas Bank, South Africa

1976 Fault geometry

• Onshore trace of fault is a segmented normal fault terminating at the shore near Groot Brakrivier (Plate 1).

Q3/R1


498


1


3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



Green & Bloch The Ceres, South Africa, Earthquake of September 29, 1969: I. Report on Some Aftershocks


• Possible association with Ceres seismicity and Groenhof and De Hoek (as shown on Fig. 39 in De Beer, 2005) faults.

• No evidence that the fault zone is still active.

Q4/R3

Gresse Worcester Quadrant Geological Map

1998 Fault geometry

• Compilation map (1:250000) showing extent of mapped trace of Worcester Fault.

• Fault does not disrupt remnants of Tg pediments to east of mapped trace.

Q5/R5

Hagedorn Silcretes in the Western Little Karoo and Their Relation to Geomorphology and Paleoecology


• Ages of 7.3 Ma and 9.4 Ma, respectively, for two samples of the silcrete caps on pediment remnants in the Little Karoo. Similar silcrete caps may be present on undeformed surfaces mapped as Tg remnants that cross the Worcester Fault.

Q4/R3



• Based on elevations and correlations of Pliocene and Quaternary marine terraces, there is no apparent deformation of the Cape region in the vicinity of the Worcester Fault or across any projected traces of the fault to the coastline.

Q4/R3



• Kango Fault may be analogue for reactivation potential of other Mesozoic faults having similar orientation in present tectonic regime.

Maximum magnitude

• Magnitude estimates for the reactivated Kango Fault based on palaeoseismic investigations may be analogue for the magnitude of ruptures that could be expected on the WOR if seismogenic.

Q4/R3 Q4/R4

Malan Riversdale Quadrant Geological Map

1987 Fault geometry

• Compilation map (1:250 000) showing extent of mapped trace of Worcester Fault.

• Short, discontinuous faults mapped in northeastern part of quadrangle do not disrupt remnants of Tg pediments.

Q4/R1

(Faults are not shown as a continuation of the Worcester Fault on CGS compilation map or by De Beer, 2005.)


499


1


3)



p(S)

Seismic Source or

Fault Geometry


Rupture Geometry



McMillan Late Mesozoic Sedimentary Basins off the South Coast of South Africa

1997 Fault geometry

• The trace of the Worcester Fault as shown on Figure 1 does not extend as far as Mossel Bay. No connection shown to offshore faults.

Q3/R3

Scharf et al. Denudation Rates and Geomorphic Evolution of the Cape Fold Belt Determined Through the Use Of In-Situ Produced Cosmogenic

10Be


• Denudation rates and geomorphic evolution of the Cape Fold Belt (CFB) determined through the use of in-situ produced cosmogenic

10Be show similarity between

catchment-averaged denudation rates (determined from river sediment samples) and denudation rates on interfluves (determined from bedrock samples)—indicative of steady state.

• 10

Be based denudation rates of the CFB fall between 2.3 ± 0.4 m/Ma and 8.8 ± 0.2 m/Ma, these rates are among the lowest in the world.

• Sample locations in the vicinity of the Tradouw River near the Viljoen road cut (as described by De Beer, 2005) locality yielded denudation rates of 5.67 m/Myr and 4.43 m/Myr (comparable to the average rate (5.4 m/Myr) measured for drainage basins farther to the east by Bierman (2012).

Q4/R4

Theron Ladismith Quadrant Geological Map

1992 Fault geometry

• Compilation map (1:250 000) showing extent of mapped trace of Worcester Fault.

Q5/R5

Toerien & Roby Oudtshoorn Quadrant Geological Map

1979 Fault geometry

• Compilation map (1:250 000) showing short, discontinuous faults mapped in northwestern part of quadrangle

Q4/R1

(Faults are not shown as a continuation of the Worcester Fault on CGS compilation map or by De Beer, 2005.)

Van Zyl Landscape Evolution of the Garden Route between the Bloukrans River and Mossel Bay

1997 Recurrence

• Surfaces with no apparent deformation near the eastern end of the mapped trace of the Worcester Fault are mapped as portions of the African Surface. These surfaces are typically capped in silcrete, ferricrete, or gravels.

Q4/R3






500

References

Bierman, P.R. (2012a). Report #1 Cosmogenic Geochronology, Southern Africa Fault Corridor

Investigation. In: Thyspunt Geological Investigations—Kango Fault Study, K. Hanson, C. Slack

& R. Coppersmith, Report No. 2012-0035 Rev. 0, 43 pp., Appendix B.3, Council for Geoscience,

Pretoria.




Du Toit, S.R. (1976). Mesozoic geology of the Agulhas Bank, South Africa. MSc thesis,


Green, R.W.E., & Bloch, S. (1971). The Ceres, South Africa, earthquake of September 29,

1969: I. Report on some aftershocks, Bulletin of the Seismological Society of America 61 (4),

851-859.

Gresse, P.G. (compiler) (1998). Worcester quadrant geological map, 1:250 000 scale, compiled

from mapping by Visser, H.N., de Beer, C.H., Glass, J.G.K., De Villiers, J., Hansen,

H., Mulder, M.P., Hartnady, C.J.H., and 16 others; map 3319, Council for Geoscience, Pretoria.


and palaeoecology, Palaeoecology of Africa 19, 371-375.

Hanson, K., Glaser, L., Coppersmith, R., Roberts, D.L., Claassen, D., & Black, D.E. (2012a).



Hanson, K., Slack, C., & Coppersmith, R. (2012b). Thyspunt Geological Investigations—Kango

Fault Study, Report No. 2012-0035, Rev. 0, 43 pp., Council for Geoscience, Pretoria.

Malan, J.A. (compiler) (1987). Riversdale quadrant geological map, 1:250 000 scale, compiled

from mapping by Siegfried, H.P., Viljoen, J.H.A., Wickens, H. de V., Toerien, D.K. & Malan, J.A.

(1984); map 3420, Council for Geoscience, Pretoria.



501

McMillan, I.K., Brink, G.I., Broad, D.S., & Maier, J.J. (1997). Late Mesozoic sedimentary basins

off the south coast of South Africa. In: African Basins, R.C. Selley (ed.), vol. 3 in Sedimentary

Basins of the World series, pp. 319-376, Elsevier, Amsterdam.

Scharf, T., Codilean, A.T., de Wit, M.J., & Kubik, P.W. (2011). Denudation rates and

geomorphic evolution of the Cape Fold Belt determined through the use of in-situ produced

cosmogenic 10Be, poster presentation given at Geosynthesis 2011, Integrating the Earth

Sciences, 8th Annual Inkaba Workshop, August 28–September 2, Cape Town, South Africa.

Theron, J.N. (compiler) (1992). Ladismith quadrant geological map, 1:250 000 scale, compiled

from mapping by Wickens, H. de V., Whittingham, J.K., Theron, J.N., Hiller, N.,

Dunlevy, J.N., Siegfried, H.P., Le Roux, P.M., Grey, P.R, Gresse, P.G. & Toerien, D.K. carried

out from 1974 to 1981, map 3320, Council for Geoscience, Pretoria.

Toerien, D.K., & Roby, D.J. (compilers) (1979). Oudtshoorn quadrant geological map, 1:250 000

scale, compiled from 1:125 000 sheet Gamkapoort–Prince Albert, 1:148 752 sheet Mossel Bay,

and from mapping by Rossouw, P.J. & Blignaut, J.J.G. (1939-40),

Haughton, S.H. & Frommurze, H.F. (1930-3), Du Plessis, P.G. (1944-4), Marlow, A.G. (1973-

74), Potgieter, C.T. (1946-47), Krynauw, J.R. (1975), and Gresse, P.G. (1974), and revised in

part by Toerien, D.K. (1973-77); map 3322, Council for Geoscience, Pretoria.

Zyl, M. (1997) Landscape evolution of the Garden Route between the Bloukrans River and Mossel Bay. MSc thesis, University of Port Elizabeth, 135 pp.