university of nigeria · university of nigeria research publications author udom, iboro demas pg/m....

University of Nigeria Research Publications

UDOM, Iboro Demas

Aut

hor

PG/M. Sc/88/6585

Title

The Use of Vertical Electric Sounding (VES) in the Study of Ground Anisotropy in Obollo-Afor Area Of Anambra State;

Nigeria

Facu

lty

Physical Sciences

Dep

artm

ent

Geology

Dat

e

October, 1990

Sign

atur

e

THE USE OF UERTICAL ELECTRIC SOUNDING ( U E S ) IN THE STUDY OF GROUND AN1 SOTROPY I N

OBOLLO-AFOR AREA OF ANAMBRA STATE, NIGERIA.

BY UDOM, IBORO DEMAS

(REG. NO. PG/M. SC/88/6585 b 1

THESIS SUBMITTED TO THE DEPARTMENT OF GEO LOGY I N THE FACULTY OF PHYSICAL SCIENCES IN PARTIAL FULFIL-? MENT OF THE DEGREE OF MASTER OF SCIENCE (APPLIED GEOPHYSICS 1.

DEPARTMENT OF GEOLOGY UNIUERSITY OF NIGERIA

NSUKKA.

O C T O B E R , 1990

- - ,'

CERTIFICATION

Mr. Udom, Iboro Demas, a postgraduate student in the

Department of Geology and with the registration Number

PG/MSc/88/6585 has satisfactorily completed the

requirements for course and research work for the degree of

Master of Science (MSc) in Applied Geophysics.

The work embodied in this thesis is original and has

not been submitted in part or full for any other diploma, 6

or degree of this or any other university.

,\ ~ r l L. I. Mamah Supervisor

D< K. M. Onuoha Supervisor

Head of Department of Geology University of Nigeria

Nsukka.

DEDICATION

This thesis is dedicated to the memory of my late

father, Elder.Demas Udom Udonnekke, my immediate senior

brother, Deacon Idongesit D. Udom; and all those who

decided to see me through this academic attainment though

they, themselves, either did not have, or did lose, or b

denied themselves the opportunity to go as far for the sake

of others.

TABLE OF CONTENTS

PAGE

CHAPTER 1:

1.1

1.2

1.3

1.4

1.5

CHAPTER 2:

2.1

2.2

2.3

CHAPTER 3:

3.1

3.2

3.3

3.4

Certification

Dedication

Acknowledgment

List of figures and Plates

List of Tables

Abstract

INTRODUCTION

General Note

Location and Accessibility

Climatic features

Objective and Scope

Literature Review

GEOMORPHOLOGY, GEOLOGY

AND STRUCTURAL SETTING

Geomorphology

Geology

Structural Setting

ELECTRICAL RESISTIVITY SURVEY

Principles

Instrumentation

Survey Operational Technique

Precautions and Practical Limitations

iii

xiii

CHAPTER I : DATA ACQUISITION, PR0C:ESSING

AND INTERPRETATION

4.1 Data Acquisition and I;*rocessing

4.2 Tnterpretation

4.2.1 General

4.2.2 Electrical Anisotropy

4 . 2 . 3 Cause of Fracturing

CHAPTER 4 : SUMMARY AND C0NCLUS:'ON

References

Appendix I Tables 3.1. - 3.7 - Observed

resistivity sounditlg results

l~nenC!!u 7 vl9l lres 5.1. - 5.7 - Observed --A C

resistivity profiles

Appendix 3 Tables 4.la - 4.7h - Direct Interpretation results

Appendix 4 Figures 6.1 - 6.7 - Computed resistivity profiles, lower and upper

azimuths of each station compared 110

Appendix 5 Tables 5.1 - 5.7 - Coefficients of apparent anisotropy per geosounding

station 119

ACKNOWLEDGMENT

Thanks be to the Almighty God who led me into the M.Sc

programme, gave me caring supervisors, and sustained us

through it in mutual relations. I sincerely and gratefully

acknowledge the wholesome supervision of the work by Dr. L.

I. Mamah of the Department of Geology, University of

Nigeria, Nsukka. His accessibility, co-operation and

understanding is highly commended. I really appreciate the

fatherly role and character of Dr. K. M. Onuoha (my other b

supervisor). Though he was on sabbatHica1 leave much of the

duration of this research, his frequent inquiry about the

project, and liberality in giving out research materials is

to be desired.

I am thankful to Mr. Ej ike Uboaja (the instrument

technician in charge of geophysical equipment in the

Department) for his quick response and personal involvement

in the geophysical investigation when his service was

needed. I appreciate, highly, the love and co-operation of

my graduate colleagues, Viz, Ifeanyi Ifionu, Okechukwu Eze,

Chike Chinwumba, Gabriel Obiefuna, Ifedigbo and others

throughout the period of this research. I wish to

acknowledge also the friendliness and concern of all my

geology lecturers, viz, the Acting Head of Department - Dr. A. C. Umeji, . Professor Ogbukagu, Dr. Ezeigbo,

Dr. C. 0. Okagbue, and Dr. K. 0. Uma. The love also of the

General Office and Workshop staff has been a great

encouragement to me.

This research was highly supported by the prayers and

daily encouragements of my christian brethren, too numerous

to mention here. I should, however, acknowledge the roles

of brother (Dr.) Akubuo and brother Simon Irtwange both of b

the Department of Agricultural Engineering in helping to

plot some of the diagrams.

I acknowledge gratefully the sacrifices of my aged

mother, Mrs Esther D. Udom; my brothers, especially Deacon

Idongesit D. Udom; sisters, brothers - and sisters-in-law; and friends, particularly Imowo Tom Udo in pushing me to

this academic level.

Finally, I express my gratitude to F. E. Nathaniel &

Co. for diligently typing this thesis.

IBORO D. UDOM DEPARTMENT OF GEOLOGY UNIVERSITY OF NIGERIA

NSUKKA.

LIST OF FIGURES AND PLATES

FIGURE TITLE

1. Topographic map of Obollo Afor

and the environs showing

structural dispositions and

geologic boundaries.

A cross-section of the area of

study along the line AB of

figure 1.

Orientations of structures

(fractures, gullies and stream

channels) in Obollo Afor area.

4.1 Schematic layout of Terrameter

instruments with Wenner

electrode configuration.

4.2 Symmetric Schlumberger electrode

configuration.

5.1 Observed - resistivity profiles, Umuezejor/Ugbaike boundary,

[a] 40° azimuth [b] 130° azimuth

5.2 Observed - resistivity profiles, Ugbaike, [a] 30° azimuth

[b] 125' azimuth.

PAGE

Observed - resistivity profiles, Umuezejor, [a] 30° azimuth [b] 120° azimuth.

Observed resistivity profiles,

Iheakpu [a] 75O azimuth [b: 165O azimuth


Iheaka [a] 22O azimuth [b] 115O azimuth


Umusigide [a] 16O azimuth [b] 106O azimuth 91 /92

Observed resistivity profiles, Ohulor

[a] lo0 azimuth [b] loo0 azimuth. * &/94

Computed - resistivity profiles (Appendix 4) l1O- lPa

Computed - resistivity profiles, 0 40 - and 130° azimuths compared - ' P i 1

Computed - resistivity profiles, Ugbaike, 30° - and 125O azimuths compared 112

Computed - resistivity profiles, Umuezejor, 30° - and 120° azimuths compared 1 1 3

Computed,- resistivity profiles,

Iheakpu, 75O - and 165O azimuths compared 1 1 4

Computed - resistivity profiles,

Iheaka, 22O - and 115O azimuths compared Computed - resistivity profiles, Umusigide, 16O - and 106O azimuths compared Computed - resistivity profiles,

Ohulor, lo0 - and loo0 azimuths compared Geoelectric Sections of Ugbaike and boundary

compared with borehole log of Ugbaike - 34

Geoelectric Sections of Umuezejor compared with 6

borehole log of Ugbaike - Geoelectric Sections of Umusigide and Ohulor

compared with borehole logs of Ezimo and

Ugbaike respectively.

Geoelectric Section of Iheaka compared with

borehole log of Ovoko.

Borehole Sections at Ezimo

Borehole (Lithologic) logs of Ugbaike

(a) Anisotropy diagram showing the directions of

fracturing in Umuezejor/Ugbaike boundary

(b) Variation of the degree of fracturing with

depth.

(a) Anisotropy diagram showing the directions

of fracturing in Ugbaike

(b) Variation of the degree of fracturing

with depth.

10.3 (a)

(b)

10.4 (a)

(b)

10 .5 (a)

(b)

10.6 (a)

(b)

10.7 (a)

(b)

Plate 1

Plate 2

Anisotropy diagram showing the

directions of fracturing in Umuezejor

Variation of the degree of fracturing

with depth.


directions of fracturing in Iheakpu


with depth.


directions of fracturing in Iheaka


with depth.


directions of fracturing in Umusigide


with depth.


directions of fracturing in Ohulor


with depth.

PLATES

Gully site by Km 2? to Ikem along

Obollo Afor - Adda road 138

Fracture setting in a house at Umuezejor. 1x6

LIST OF TABLES

TABLE

1

TITLE

Generalized Stratigraphic

Succession of the Anambra basin

Structural orientations at Ugbaike

Structural orientation at Umuezejor.

Structural orientations at Iheakpu

Structural orientations at Iheaka

Structural orientations at Umusigide

Structural orientations at Ohulor

Observed - resistivity sounding result,

Umueze j or/Ugbaike boundary, 40° azimuth

Observed - resistivity sounding result,

Umuezej or/Ugbaike boundary, 13 o0 azimuth

Observed - resistivity sounding result, Ugbaike, 30° azimuth

Observed - resistivity sounding result, Ugbaike, 125O azimuth

Observed - resistivity sounding result, Umu ezejor, 30° azimuth

Observed - resistivity sounding result, Urnuezejor, 120° azimuth

PAGE

Observed - resistivity sounding result, Iheakpu, 75O azimuth

Observed - resistivity sounding result, Iheakpu, 165O azimuth

Observed - resistivity sounding result, Iheaka, 22O azimuth

Observed - resistivity sounding result, Iheaka, 115O azimuth

Observed - resistivity sounding result, Umusigide, 16O azimuth

Observed - resistivity sounding result, Umusigide, 106O azimuth

Observed - resistivity sounding result, Ohulor, lo0 azimuth

Observed - resistivity sounding result, Ohulor, loo0 azimuth

Direct interpretation results,

Umuezejor/Ugbaike boundary, 40° azimuth


Umueze j or/Ugbaike boundary, 130° azimuth


Ugbaike, 30° azimuth


Ugbaike, 125O azimuth

4.3a Direct interpretation results,

Umuezejor, 30° azimuth

4.3b Direct interpretation results,

Umuezejor, 120° azimuth

4.4a Direct interpretation

Ihkakpu, 75O azimuth

4.4b Direct interpretation

Iheakpu, 165O azimuth

4.5a Direct interpretation

Iheaka, 22O azimuth

4.5b Direct interpretation

Iheaka, 115O azimuth

Direct interpretati,on

Umusigide 16O azimuth

Direct interpretation

results,

results,

results,

results,

results,

results,

Umusigide, 106O azimuth


Ohulor lo0 azimuth


Ohulor, loo0 azimuth

Coefficients of apparent anisotropy

per geosounding station (Appendix 5 )

Coefficients of apparent anisotropy for

Umuezejor/Ugbaike boundary


Ugbaike 123


Umueze j or 1 -22


Iheakpu 123

Coefficients of apparent anisotropy for 1,

Iheaka 124


Umus igide 125


Ohulor 1.26

Classification of degree of homogeneity. &

ABSTRACT

The area of study lies between kbitudes 6' 5 3 W

and 6' 5 6 H andLon itudes 7' 2ar6 and 7' 35r6, and 9 falls within the Anambra basin of Nigeria. It has an

undulating topography with some deep valleys and high

hills. Geologically, the area is underlain by loose,

unconsolidated to poorly consolidated sandstones and

gravels that are undergoing ferruginisation and *

lateritization. The high hills are constituted by

ironstones, claystones and some lateritic cap of Nsukka

Formation, while underneath the sandstones and gravels is

the sequence consisting of alternation of shales,

sandstones and mudstones of the Mamu Formation.

Structurally, the area is highly eroded downslope by

surface runoff, and fractures abound on the scarp surfaces.

Surface mapping has revealed high degree of

correlation between the trend of fractures, erosion and

stream channels. Electrical anisotropy of the ground due to

fractures was investigated geophysically using vertical

electric sounding (Schlumberger) method. Sounding was

executed in each of seven stations located in the area

along the two principal directions of the local fractures

(NNE-SSW/ESE-WNW or NE-SW/NW-SE, average).

Variation in the values of apparent resistivity from

traverse to traverse and with depth suggests ground

anisotropy which is related to the intensity and trend of

fractures observed at the surface.

CHAPTER 1 INTRODUCTION

1.1 GENERAL NOTE

It has been observed that many parts of Anambra State of

Nigeria are fractured to a great extent, coupled with a high

degree of gully erosion. In such places existence of roads,

buildings, trees and farmlands are seriously threatened by

intensive erosion and fracturing. Erosion control measures

have been defied, structures and trees being pulled down by *

overland flow along Obollo Afor - Adda road in the study area, v-1 Fracturing of buildings and land in this area

has caused the inhabitants great fear of an impending

earthquake.

A reconnaissance survey of the area was carried out

between December, 1989 and February 14th, 1990 to obtain a

first hand information on the geology and structural setting

in the area. This survey was repeated during the rainy season

at the end of July, 1990. It was observed that the area is

predominantly covered with loose, unconsolidated to poorly

consolidated sandstone which makes it highly

susceptible to surface-water erosion. Almost all the

buildings in the area are fractured. To say the least, the

degree of surface erosion, and fracturing both of the walls

of buildings and roads in the area should not only arouse

the fears of the inhabitants, but deserves immediate and

remedial attention of researchers (Governments and

universities).towards finding a lasting solution to the

problem.

1.2 LOCATION AND ACCESSIBILITY +

The area of study is dominantly a part of Isi-Uzo

Local Government Area coupled with a relatively small

portion of Igbo-Eze Local Government Area, both of Anambra

State. It lies between longitudes 7' 28IE and 7' 35IE

and latitudes 6' 53IN and 6' 56IN, an area of

approximately 72.0 sq.km. Major towns and villages include

Iheaka (Likke), Iheakpu, Umusigide, Adda, Umuezejor,

Umundu, Ohulor and Ugbaike in Enugu-Ezike. Fig.1 shows the

area copied from maps of Nsukka sheet 287 and Igumale sheet

288 published by Geological Survey of Nigeria, 1965 and

19 64 respectively.

The area is accessible by a fine network of roads, and

footpaths too numerous to insert in the map. The new road

4

from 9th mile Corner to Makurdi has been carefully

inserted, guided by the Administrative map of Anambra

State, 2nd Edition (1985).

1 . 3 CLIMATIC FEATURES

The Survey area has been classified under the tropical

rain forest/quinea savanah belt of Nigeria. It has two

climatic seasons - the wet and the dry seasons annually. The wet season commences from April and ends in September

while the dry season lasts from October to March. The wet 4

season is marked by heavy rain falls in the months of May

to July, while the dry season has the greatest severity of

cold, dry and windy weather during its harmattan period

between November and January. These climatic cycles are

caused by the "North - South fluctuation of the zone of discontinuity between the dry continental (Saharan) air and

the humid Atlantic airn (Garnier, in Ozoko, 1988).

Ozoko (1988) gave the mean annual temperature of about

0 30 c, and mean annual humidity of 75% for the area.

1 . 4 OBJECTIVE AND SCOPE

This work has the following objectives and limits:-

(a) To measure the fracture trends and the

5

attitudes of streams and erosion channels in the survey

area, and attempt their correlation.

To carry out vertical electric soundings

(VES) at selected locations in the area with

the aim to determine the ground anisotropy

due to continuity, or otherwise, of the

fractures in the subsurface.

To determine, or speculate, based on the

above findings the probable cause(s) of the

fracturing in the area. +

1.5 LITERATURE REVIEW

Little is known of the application of electrical

methods in the study of ground anisotropy due to

fracturing. The few known examples include the works of

Mallik et al, (1983) and Mamah and Ekine (1989). In

particular, no geophysical work has yet been done in the

area of study. However, record abounds on studies carried

out on the regional geology of Nsukka which part the study

area is.

Preliminary geologic (lithologic, stratigraphic,

structural) description of rocksin the region can be dated

back to the work of Bain (1924), Simpson (1954) and

6

De Swardt and Casey (1963) on Nigerian coal fields. A

biostratigraphic correlation of sediments of the Southern

Sedimentary basins, including those of Maau Formation,

Ajali Sandstone and Nsukka Formation underlying the study

area, was attempted by Reyment (1965). Other geologic

aspects of these sediments, such as, tectonic evolution and

textural characteristics, have been variously studied by 0

short and Stale (1967), Nwachukwu (1972), Hoque (1976,

1977), Hoque and Ezepue (1977), Banerjee (1979) and Unuevho

(1983). +

Available literature gives credence to the works of

Grove (1951), Floyd (1965) and Ofomata (1965) as remarkable

preliminaries on the development and impact of erosion

gullies in some parts of Anambra State. Further researches

have been carried out by others, such as Ogbukagu (1976),

Technosynesis (1978), Nwajide and Hoque (1979) Egboka and

Nwankwor (1985) , Uma and Onuoha (1986) and Okagbue (1986)

on gully development in Agulu - Nanka - Oko, Enugu area and in some parts of Imo and Cross River States. These workers

concentrated on the causes of gully development in

South-Eastern Nigeria, and on the failure of control

measures and made suggestions on more durable control

measures to the gully problem. They paid little or no

attention to the other possible threat to life - the fracturing of both land and buildings in the State

(Anambra).

Nevertheless, Unuevho (1983) did make some

observations on the fracture/joint pattern in the area of

study. He noted the existence of two-directional,

0 tight-spaced, vertical joints (67' - 90 dip), striking

60' azimuth (ENE-WSW) and 165' azimuth (NNW-SSE), and

believed that the fractures d e n products of residual stress

from Santonian tectonic episode, acting in the South-west +

and North-east directions respectively.

CHAPTER 2 GEOMORPHOLOGY. GEOLOGY, AND STRUCTURAL SETTING.

2.1 GEOMORPHOLOGY

The survey area has an undulating topography with few

scattered hills and lowlands (fig. 2). The hills are

constituted by remjdnants of Nsukka Formation, mainly

intercalation of ironstone layers, mudstones, and lateritic

cap that have withstood denudational activities of the

geologic past. Much of the surface rocks have been highly

eroded downslope exposing the red earth and laterite cover b

of the underlying Ajali Sandstone. The area is thought to

have been uplifted during the Miocene-Pliocene, and exposed

to intense erosional activities (Simpson, 1954).

The topographical setting of the area constitutes part

of Enugu escarpment running roughly North-South from Enugu

through Nsukka to Eha-Alumona, Ehandiagu and Obollo-Afor.

In the study area, the escarpment tends to have a mean

vector in the Northwest - Southeast direction with its peak at Obollo-Afor (a height of about 488.0m above sea level - a.s.1.) and its lowest point at Adda (about 24.0m a.s.1.).

The h i g h e s t g r a d i e n t of t h e t o p o g r a p h y i s s l i g h t l y i n t h e

S o u t h - e a s t d i r e c t i o n , where wide and deep g u l l i e s ( p l a t e 11,

s t r e t c h i n g o v e r s i x k i l o m e t r e s , have b e e n created by

s u r f a c e r u n o f f a l o n g b o t h f l a n k s of t h e Obollo A f o r - Adda

road . Both t r e n d and magn i tude of t h e g u l l i e s show t h a t

e r o s i o n i n t h e area h a s been d o m i n a n t l y c o n t r o l l e d b y f o u r

factors, v i z : (1) s o i l e x p o s u r e d u e to loss o f v e g e t a t i v e

c o v e r ; (2) g r a d i e n t of t h e topography ; ( 3 ) t h e loose and

p o o r l y c o n s o l i d a t e d r e d e a r t h and l a t e r i t e c o v e r of t h e

A j a l i S a n d s t o n e u n d e r l y i n g most p a r t s of t h e a r e a , a n d @

(4) f r e q u e n t and heavy r a i n f a l l s .

Egboka (19831, work ing o n Nsukka a r e a and t h e

e n v i r o n s , o b s e r v e d t h a t s u r f a c e w a t e r s were a b s e n t on

t h e pe rmeab le members of t h e A j a l i S a n d s t o n e , b u t w e r e

h i g h l y d e v e l o p e d o n t h e less pe rmeab le s h a l y beds of

Nsukka and Mamu Format ion . I n t h e s t u d y a r e a , t h e f e w

streams and r i v e r t r i b u t a r i e s ( n o n e o n Nsukka Forma t ion )

r u n a l o n g N o r t h s o u t h to NortWest - S o u t h e a s t d i r e c t i o n

of t h e e sca rpmen t .

11

2.2 GEOLOGY

Obollo Afor area constitudes part of Anambra basin of

Nigeria and is underlain by three Formations - the Mamu Formation, Ajali Sandstone, and Nsukka Formation (all upper

Cretaceous to lower Paleocene) in upward succession. These

were previously known and described respectively as

theLower Coal Measures, the False - bedded Sandstone, and the Upper Coal Measures (Tattam, 1944; simpson, 1954). The

stratigraphic sequence of the basin is shown in table 1.

The Ajali Sandstone predominates the surface geology +

of the area, with exposures of remnants of the overlying

Nsukka formation only at the hills and their immediate

environs. Hoque and Ezepue (1977) supposed that the Ajali

Sandstone and other Sandstone units of the Anambra basin

were formed by "profound chemical weathering of granitic

rocks of the Cameroun highlands in a climatic environment

very similar to the present day humid conditionsgg.

Egboka (1983) gave the total thicknesses of the three

+ + Formations as 400m, 330m , 330m respectively. Based on

boreholes drilled within the area of study and surface

QS exposures, the total thickness,of these Formations are

estimated at 20m. 200m+, and 50m' respectively.

HOLOCENE

TABLE

PLEISTOCENE

1: GENERALISED STRATIGRAPH

7 PLIOCENE

MIOCENE

PALEOCENE

Marine detaic deposits, ~lluvium

Benin Formation

Ogwashi - Asaba Formation

Ameki Formation/~anka Sands Imo Shales

I Nsukka Formation b

Maestrichtian I Aj ali Sands tone

Turonian I Eze-Aku Shales

,

Senonian

Albian

Aptian

Mamu Formation

Cenomanian

AbakalikiIAsu

River Group

Campanian

Santonian

Coniac ian

Odukpani Formation

(Adapted from Reyment, 1965)

Nkporo Shale

Awgu Shale

13

The Mamu Formation is constituted of layers of

carbonaceous shales, sandy shales, mudstones, sandstones

and siltstones with some lithologic units varying in

thicknesses between 50cm and 100cm. At Adda, around km 18

to Ikem along Obollo Afor - Obollo Eke road (four kilometres outside the study area) the above lithologic

units are exposed. Sandstone units of this formation are

friable, and poorly cemented, while the shale members are

highly fractured*

The Ajali Sandstone conformably overlies the Mamu 4

Formation. It is constituted by white, sometimes

iron-stained sandstones. Hoque and Ezepue (1977), and

Egboka (1983) respectively reported the occurrence of this

beds of white to pinkish claystone and shale beds at

various intervals, some claystones having plant

impressions. The Sandstone Formation is typically composed

of friable, fine to coarse grained, poorly to moderately

sorted, subangular to subrounded sands with characteristic

cross-bedding. In the survey area, the formation is almost

entirely overlain by the transitional (reddish) sandstone

between Nsukka Formation and the Ajali Sandstone.

The overlying Nsukka Formation has been considerably

eroded away leaving thin layer of highly weathered and

ferruginised sandstone around the hills.

14

Ironstone layers, boulders and pebbles, claystones and some

lateritic cap of this formation abound at the residual

hills. According to Reyment (1965) the general lithology

of this formation includes sandstone, carbonaceous shale,

clay, siltstone and bands or lenses of impure coal. The

shale units are laminated and fissile, giving rise to

numerous sets of joints; while the sandstone units are fine

to medium grained, poorly consolidated and friable. The

claystone has fossil leaf impressions (Egboka, 1983).

Nwajide and Hoque (1976) observed that the lateritic

overburden of this formation was over 15m in some 4

flat-topped hills. Composition (they stated) is dominantly

iron oxide with iron content varying from 22.0 to 53.0%,

and minor amounts of clay, gibbsite, quartz and amorphous

silica. The laterites are highly permeable.

STRUCTURAL SETTING

Effect of surface run off is manifested in many

channels that have been differenti#ally eroded downslope.

Deep gullies (between less than one metre and ten metres)

have been created along both flanks of Obollo Afor - Adda road. Similar effect of rain wash is observed at Ugbaike

- and Umuezejor where roads have been cross-cut by . f b o d a

- Though the erosion channels are downslope everywhere in the area, careful observation reveals that they have

followed lines of weakness, some of which were most

probably pre-existing fracture traces.

A t Ohulo r , , for i n s t a n c e , a z i m u t h s o f g u l l i e s measu red i n c l u d e 0 0 0 0 0 0

120 , 1 0 0 , 1 3 0 , 1 0 5 , 1 1 0 , t h e mean ( 1 1 3 ) o f which

c o r r e s p o n d s t o one o f g e n e r a l t r e n d s o f t h e s t r u c t u r e s i n t h a t

a r e a ( f i g . 3 ) . A t Umuezejor, two a d j o i n i n g e r o s i o n g u l l i e s have 0 0

o r i e n t a t i o n s i n 40 and 1 3 0 a z i m u t h s r e s p e c t i v e l y . #

Brun ton c o m p a s s / c l i n o m e t e r was u s e d t o m e a s u r e d i r e c t i o n s o f

t h e e r o s i o n c h a n n e l s and f r a c t u r e s . Wid th s o f t h e f r a c t u r e s were

measured w i t h V e r n i e r c a l i p e r s . F r a c t u r e s are u b i q u i t o u s i n t h e

a r e a , and a r e commonly found r u n n i n g f rom t o p o f h o u s e w a l l s t o

t h e f l o o r , and on r o a d s i n two o r t h o g o n a l o r a l m o s t o t h o g o n a l

d i r e c t i o n s . T a b l e 2 . 1 - 2 .6 p r e s e n t s t h e o b s e r v e d s . t r u c t u r a 1

orientation^ i n t h e a r e a and t h e i r f r e q u e n c y d i s t r i b u t i o n s .

F i g u r e s 3 ( a - f ) show t h e p r i n c i p a l o r i e n t a t i o n s o f t h e

s t r u c t u r e s . I n g e n e r a l , t h e s e s t r u c t u r a l t r e n d s c o r r e l a t e w i t h

t h e ma jo r f r a c t u r e s o f t h e Lower Benue B a s i n which t r e n d s NE-SW

a n d NW-SE. The r e a d e r I s r e f e r r e d t o t h e s t r u c t u r a l map o f

Nigerla, 1385.

Structural o r i e n t a t i o n s are g r o u p e d w i t h c lass i n t e r v a l s of 0 0 0

30 o v e r a r a n g e oE 0 --I79 , and are p r o j e c t e d t o t h e o p p o s i t e 0 0

r a n g e of 1 8 0 - 360 t o a c c o u n t f o r a z i m u t h a l d i r e c t i o n s .

(a) UGWKE

l o . SSE S

(d 1 IHEAKA (n =27)

S ( c ) IHEAKA (f) OHULOR

NOTE: n = number of observations - FIG- 3 ORIENTATION O F STRUCTURES ( fractures, gullies

and stroam channels) IN OBOLLO-AFOR AREA

TABLE 2.1 STRUCTURAL ORIENTATIONS AT UGBAIKE - OBSERVED VALUES AND CLASS FREQUENCY DISTRIBUTIONS

OBSERVED VALUES (in degrees)

50, 75, 50, 105, 115, 50, 120, 50, 15, 50, 120,

125, 70, 20, 45 25, 125, 55, 105, 75, 30, 50,

55, 30, 50, 130, 10, 25, 70, 50, 50, 125, 100

(n = 33)

FREOUENCY DISTRIBUTION

CLASS (Degrees) ------------ FREQUENCY ------------ PERCENTAGE ------------

TABLE 2.2 STRUCTURAL ORIENTATIONS AT UMUEZEJOR - OBSERVED VALUES (in degrees) 45, 135, 10, 125, 135, 135, 160, 40, 25, 30, 35,

45, 107, 25, 55, 145, 25, 110, 5

(n = 30)

FREQUENCY DISTRIBUTION

CLASS (Degrees) ------------ FREQUENCY ------------ PERCENTAGE ------------

NOTE : n = number of observations.

TABLE 2.3 STRUCTURAL ORIENTATIONS AT IHEAKPU


140, 50, 150, 135, 143, 0, 90, 26, 120, 125,

90, 80, 130, 0, 90, 28, 0, 12, 5, 7, 5,

5, 100, 95, 95, 100, 95, 15. (n = 28)


CLASS (Degrees)

FREQUENCY ------------ PERCENTAGE ------------

NOTE : n = number of observations. ...........................................................

TABLE 2.4 STRUCTURAL ORIENTATIONS AT IHEAKA


155, 155, 155, 140, 155, 100, 90,102,

103, 55, 60, 24, 48, 33, 140, 51, 141,

135, 145, 142, 52, 50, 150, 60, 0, 150, 79

(n = 27)


l CLASS I I (Degrees) 10-29 130-59


20

TABLE 2.5 STRUCTURAL ORIENTATIONS AT UMUSIGIDE AND ADDA


90, 40, 45, 140, 140, 100, 110, 140, 105, 0, 0,

4, 0, 90, 90, 30, 18, 10, 30, 40, 50, 120,

135, 60, 170, 115, 0, 120, 18, 20, 22, 25, 15,

160, 160, 165, 5, 15, 15, 15, 108, 4, 20, 103,

100, 100, 100, 100, 110, 115, 35, 130, 0, 0,

15, 110, 93, 4. (n = 58)


CLASS (Degrees)

FREQUENCY ------------ PERCENTAGE ------------

NOTE : n = number of observations. ...........................................................

TABLE 2.6 STRUCTURAL ORIENTATIONS AT OHULOR


62, 60, 62, 0, 140, 122, 153, 103, 85, 170,


CLASS (Degrees) ------------ FREQUENCY

PERCENTAGE ------------


CHAPTER 3: ELECTRICAL RESISTIVITY SURVEY

3.1 PRINCIPLES

If a direct current is passed through a passive

circuit element, the ratio of the potential difference

across the element to the amount of current flowing through

it equals its electrical resistance, R which is constant

for the element. In voluminous materials, R is often

considered in terms of resistivity, .? which is the

resistance of a unit volume of the material, and is

proportional to R. Thus, .? = RA/L, where A is the b

cross-sectional area of the medium through which the

current passes, and L is the linear dimension of the

material measured in the direction of the current.

Resistivity of earth materials varies over a long

range depending on the average electrical properties (most

importantly, conductivity) of the various components of the

medium, viz, the lithology, porosity, permeability, and

principally the fluid content and quality. This

resistivity is designated apparent resistivity, fa since

the earth is heterogeneous and anisotropic; and is given by

fa = FR, where F is a factor of linear dimension

characteristic of the geometry of electrode configuration

used in the survey.

With Wenner array, for instance, in which four electrodes

are arranged collinearly with equal spacing, F = 2ra,

where a is the interelectrode spacing (fig. 4.1).

In standard resistivity survey, a direct current (I),

or very low frequency alternating current is passed into

the ground via two electrodes while the ground potential is

measured across two other electrodes. It has been

demonstrated (e.g. Telford et al, 1976) that in a four - electrode configuration, such as in fig 4, over an

homogenous and isotropic medium the potential difference b

(AV) measured across the two potential electrodes, PI and

P2 is given by the relation:

where r, , 5, ra3 and re are CL &,fi C Z f cL&, and P$,,c2 respectively, and is given as 6 for the heterogeneous and anisotropic case. Ci and C~are current electrodes. For the

symmetric Schlumberger configuration fa is transformed and

approximated to

2J T' where I, = 1/2 C1 C2 and 1 = q 2 Ppi p2

I

V- BOX

F I G 4.1 SCHEMiiTIC LAYOUT O F T E R R N T E R INSTRUMENTS WITH WENNER ELECTRODE CONFIGURATION.

(courtesy of ~ b e m )

F I G 4.2 SYMMETRIC SCHLUMBERGER ELECTRODE CONFIGURATION.

In homogeneous and isotropic media fa should be

constant in both the horizontal and vertical directions.

In heterogeneous and anisotropic media, such as the earth,

the apparent resistivity could vary in one, two or three

directions. Variation of the resistivity may then be

interpreted in terms of stratification of the earth, layer

thicknesses and resistivities, lithology, porosity and

permeability, fluid content and quality. The application

of electrical resistivity technique in the exploration of

fracture zone is based on the fact that a fracture usually b

contains materials that are more or less conductive than

the host or surrounding rocks. Consequently, apparent

resistivities measured across or along the fracture zone

show a departure (anomaly) from the normal value for the

host rock. Thus, such zones of discontinuity can be traced

laterally, or probed vertically using the electrical

resistivity method.

INSTRUMENTATION

A set of Abem A.C. Terrameter equipments, consisting

of a current - transmitting unit (G - box, type No. 5312), a receiving unit (V - box, type No. 5311), two current - transmission cables (on reels), potential cables, four

metal electrodes and three hammers, was used. Auxiliary

equipments included a Brunton compass for profile

orientation, matchet for clearing of traverses, and vessels

for salt solution. b

The Abem A.C. Terrameter is a compact, yet a light

weight instrument designed to give high quality results

even under difficult conditions, especially in tropical

environments. Combined weight of the G - and V-boxes is only 13.5kg (301b). The G - box consists of a transistorized oscillator fitted with twelve 1 . 5 ~ dry

batteries and operating controls. It supplies a square

wave alternating current with a frequency of about 4Hz.

The V-box contains the potential - measuring units (consisting of a switch, attenuator, amplifier,

microammeter and two standard 9v dry batteries) and a

reference potentiometer circuit. Special features of the

Terrameter instruments include:-

- High Sensitivity and accuracy :- it has a measuring

range of 0.003 - 10,000 Ohms, and an accuracy better than 3% down to 0.01 Ohm and 10% for readings as

low as 0.003 Ohm.

The application of a very low frequency square wave

alternating current eliminates electrode polarization

and minimizes capacitative effects.

Possible leaking current between the oscillator and

voltmeter circuits is eliminated by the use of two

separate units for current supply and measurement.

The amplifier is designed so as to effectively

attenuate noise from power lines, current - carrying cables, or ground telluric current.

4 There is ease and speed of operation as a consequence

of well combined operating controls. Accurate

readings can be taken in 30 seconds or less.

The instrument can be used in structural

investigations down to a depth of 600 metres.

3.3 SURVEY OPERATIONAL TECHNIQUE

Vertical electric soundings were carried out at seven,

carefully selected points in the area between April 23rd

and May 5th, 1990. Care was taken within practical

limitations to run the traverses in two azimuths falling

within the range of the local fracture orientations

(Fig. 1) .

Four men constituted the sounding crew; one in charge

of instrument operation while the others moved the

electrodes. Symmetric Schlumberger array (radial) in which

two outer current electrodes and two inner potential

electrodes are collinearly and symmetrically arranged over

a common centre, was employed (Fig. 4.2). Maximum Current

electrode spread (AB = CIC2) was 400 metres, while that of

the potential electrodes (MN = P2) was 28 metres. Most

of the spread dimensions satisfied the principle that MN 4

should be small compared to AB (that is, MNs 1/5 AB).

Both current and potential electrodes were metals driven

into the ground so as to make good electrical contact.

Loose earth materials, such as crop ridges and heaps in

farmlands, were as much as possible avoided; and salt

solution was used to wet electrode contact with the ground

in dry areas.

A complete circuit connection of the electrodes with

the ground, cables, and instruments is shown in Fig. 4.1.

The principle is, however, illustrated with Wenner array in

which the interelectrode spacing, a is constant. In this

thesis, CI , Pi and P2 are denoted respectively as A, B,

M and N (Fig. 4.2). E and T are the oscillator and power

transformer respectively, of the G - box; while A (of the instrument), M and R are the amplifier, microammeter and

potentiometer of the V-box.

The G-box is connected to the current electrodes Cl and C2

(or A and B), while the V-box is connected to the potential

electrodes PI and P2 (or M and N). The G - and V- boxes

are inter-connected and switched on. Then reading is

taken.

3.4 . PRECAUTIONS AND PRACTICAL LIMITATIONS

There are some problems, practical limitations, and

precautions to face in electrical resistivity survey.

Some of the problems are due to instrument design or b

setting in the field, while others are due to the

operational efficiency of the field operators. The

Abem A.C Terrameter offers good results when the

instruments are operated by experienced men with

necessary precautions and care being taken. Problems

associated with resistivity survey, and with

Terrameter instruments in particular are presented

below: - - Output voltage generated by the transmitting

unit range from 100 volts to 400 volts, therefore

the primary current is dangerous. The current

electrodes should not be touched when current is

flowing. In this survey, care was taken to ensure

that the oscillator was switched off before signal

was given to move the electrodes and that they were

fixed to the ground before switching on.

- There is, usually, high probability of

induction effects that can disturb observations,

resulting from electromagnetic coupling between the

G - and V - boxes, between the cables plus reels and ground. Electromagnetic coupling between G-

and V- boxes could be minimized by always placing

thei.r short sides parallel to each other, about

0.5m apart. The instruments were operated by a

highly experienced technician. Some care was also

taken to avoid current and potential v4.5 b

touching each other, or running parallel over long

distances.

- Topographic undulation can have large

influence on measurements obtained in the field,

especially if the undulation does not reflect the

subsurface structure and if the rock formation is

not homogeneous and isotropic. To avoid this

topographic effect, profiles were run over

relatively flat lands.

- Structural, cable and jungle interference: In

many parts of the area of study there are either

houses scattered about, or high tension cables, or

jungles that interfere with one or both of the

planned traverses. It was possible to avoid the

later two objects; but in all, where the

interference could not be completely avoided, some

degree of deviation from a straight traverse was

CHAPTER 4 DATA ACOUISITION, PROCESSING AND INTERPRETATION

4.1 DATA ACOUISITION AND PROCESSING

Radial vertical electric soundings (VES) were carried

out at seven stations distributed over the area of survey.

Two orthogonal sounding traverses were determined at each

location depending on the attitudes of fractures in the

local environment, and apparent resistivities of the ground

were calculated against spacing (AB/2 ) from the values of

ground resistances measured in the field (Table 3.1 -83.7,

pagea $56-79). The apparent resistivity was computed from

the relation,

2 2 1

where L and 1 are half the current electrode separation,

and half the potential electrode separation respectively,

and R is the measured resistance of the ground (R =Av/I).

Graphs of the field observations (apparent resistivity

versus spacing) were plotted (Figs. 5.1 - 5.7,pa9es - Smoothing of the curves was done by shifting the segments up or down to obtain the average and continuous

profile.

Apparent resistivities of the smoothed curves, computed

against AB/2 were used as input data for direct (computer)

computation of the thicknesses and resistivities of each

layer of the ground for each station (Tables 4.1 - 4.7, 6409). The computer output is a quantitative and an

automatic interpretation of sounding curves using modified

Dar Zarrouk functions, after Zohdy (1975). The

interpretation approach is an iterative method which

generally involves comparison of the field data with the B

data derived from a layer model obtained by an approximate

method (Koefoed, 1979). Resistivities and thicknesses of

the layer model are adjusted in steps until an adequate

agreement between the model and field data is obtained. In

the particular approach of Zohdy (1975), Mamah and Ekine

(1989) summarized the pebculiarities of the technique as

follows:

"This approach is based on inversion of the vertical

electrical sounding curves (VES) without first

transforming it into its corresponding total Kernel

function curve (TKF). Furthermore, unlike most of the

direct interpretation methods the interpreter does not

have to make an initial assumption on the number of

layers or about their resistivities and thicknesses.

Instead, the VES curve is digitized (at the rate of

six points per logarithmic cycle) and the number of

layers is automatically fixed as equal to the number

of points on the digitized curve. For the first

approximation, the points on the digitized VES curve

are considered to be points on a modified Dar Zarrouk

(MDZ) curve which is solved for layer thicknesses and

resistivities. The TKF curve for this layering is

calculated by Sundefs (1949) recursion formula, and b

the VES curve is calculated by convolution using

Ghoshfs coefficient (Ghosh, 1971a). The calculated

and observed VES curves are compared and through an

iterative formula, a new MDZ curve is calculated,

solved for layering and a second VES curve is

calculated. The iteration continues until a fit

within a prescribed tolerance is obtained between

observed and the calculated VES curves."

The advantage of this approach is that the total

kernel function values for a given layer determined by

recursion formula are more accurate than those obtained by

transformation of a VES curve. It can be seen from tables

4.1 - 4.7,PafgeS 6-189)that there are very little or no

differences between the observed and the calculated values

of the apparent resistivity.

Figures 6. 7 - 6.7 (.ms, l l l - l i 7 ) compare the resistivity

profiles along the two azimuths of each station.

4.2 INTERPRETATION

4.2.1 GENERAL

Apparent resistivities of the various stations were

compared with the direct interpretation result, and with

the few borehole (lithologic) logs of the area. The

geoelectric profiles (apparent resistivity curves) show a @

two - to four - layer earth (Figs. 6.1 - 6.7, pgs. ¶11-11")),

analysed through a direct interpretation programme into

multiple layers with corresponding computed resistivities

(Figs. 7.1 - 7.4). This multiple - layer earth is confirmed by the borehole logs. Their absence in the

apparent resistivity curves should be due to layer

suppression - a condition in which a layer of resistivity intermediate between the one on top of it and that below

can not be detected in the resistivity curve. Suppression

may also arise when the intermediate layer is too thin.

Compared to the enclosing layers unless its resistivity is

very high.

There is generally a progressive increase in layer

resistivities in each station, except at the boundary

between ~muezejor and Ugbaike (Fig. 7.1) and along 30°

azimuth at Ugbaike (Table 4.2a,page 98).

Coarse red sand

1

Gravel . , I I

Z ~ I ' S ~ i t d (~r-lci'

white sand, I some g m w ~ I below 92m

I

STATIC 95 - WATER LEVEL V 113m. I I 117 -

Coome yellow I and white sand I

Coarse white 1 sand I

-I-- EXPLANATION

LZ) Resistivfslvaries from 1542.,87Qm to 2562-76nm. but rises t o the mnge uf 20,441-87-26,806.9Qnm b e t w n the depth of QMW'1.55m

mResi&vity value is 26,945.2a m Figures after the locations are calculated elevations above sea level from contour values in the map Water level as at May 26th. 1977. (Courtesy d Anambm State

Water Corporafion) Ground level as at 1965

F IG71 GEOELECTRIC SECTIONS OF UGBAIKE AND BOUNDARY COMPARED WITH BOREHOLE LOG OF UGBAIKE.

CEOELECTRIC SECTION I BH W.61 W K E 1469.0 m) 1 GEORECTRIC SECTKIN

I 7636 79-51

GEOELECTRIC

' Coarse red I sand I

Laterite

Gravel

Coarse red and white sand, some gravel below 9.2 m

sand 1 Coarse white I

sand ,

MPlANATION Ground level as a t 1965

FIG 7.2

Water level CIS at May 26th. 1977 when the well was completed (Courtesy of Anambra State Water Corporation)

beosouddigg stations at MEAKPU and UMUEZEJOR are respectively 1.5km bni'075krn(approx-) from Ugbake borehole

Elevation of the station above sea level ( f r om 1965 topoy mphic map)

GEOELECTRIC SECTIONS OF IHEAKPU AND UMUEZEJOR COMPARED WITH BOREHOLE LOG OF UGBAIKE.

1 GEDELECTRIC SECTION ' BH NO. 1220 EZIMO

. . . . I stone

. . f :- --,I: Sand- . ' . I st one

. . stone

BH NO- 61 1 UGBAIKE I GEOaECTRIC SECTION

. - ;:: Coarse ,:-: '. red and! ': white 1 . . .-

. $ . . sand, 60-0 * . . some I - . \ . .. . - , .. -. .

. below I : . : 92m

I

sand ',

ELECTRIC BASEMENT

Ezimo is 3.50km (merage) from Umusigide. Ugboike is appr oximately ZOkm from 0 hulor

I3 Ground elevation above sea level (from topographic map d 19651 mGround level ca at 7965

FIG 7.3 GEOELECTRIC SECTIONS OF UMUSIGIDE AND OHULOR COMPARED WITH BOREHOLE LOGS OF EZlMO AND UGBAIKE RESPECTIVELY

, -- - ---- - - - NOTE - 8 Water level as at May 16th, ?977 when the well was

completed (Courtesy of Anambra State Water Corpmtionl. PY Ovoko borehold site is the nearest to I h d a , less than

4km f rom the VES State Ground elevntion above sea level as at 1965

GEOELECTRIC SECTION + I BWEHOLE NO 58, OVOKO 1 (LZ6.O rnf

IHEAKA (L26X)rn )

FIG. 7.4 GE OELECTRIC SECTION OF IHEAKA COMPARED WITH BOREHOLE LOG OF OVOKO

RESTNITY Cn rn)

721 66 - 5696-11 - = 11.81

5309 16455

.70 124 03.25

- 20.90

39x104-3.6~ 10s 26.4 8

22

29.56 31-66 32

38-96

48

59.99 . 63.34

@ STATIC WATER LEVEL

- q:101.W**

1L6

DEPTH (m)

721 '.. . ' .- . .* . . . : . .. .

. .;.-:+., - . . . . . . . . : : : . . -.. . . . . r.0:.

~2.5::';;~ ., . -, ;: : . . :.:: . . . . . . '. . . .

58: " ' . ' .. - - . ... , : . .. o .' '.

a < - -

: , . .: . . * * * 0. ( '@ . . : .. . 0 ...' --.

Red sand

Laterite

Laterite /Gravel B

Red and White Sand

Sand / Laterite

Bands of White and Yellow Sand with Bands of Gravel

L

LOG - . . 1 . . - . . .. .

LTTHOL~GY

The resistivity values range from 605.05 Ohm-m at the

surface at Iheaka to 699, 663.39 Ohm-m at the greatest

depth of penetration at Ikeakpu. Depth of investigation

too varies from about 31. Om along 30° azimuth at Ugbaike

to 113.0m along 40° azimuth at the boundary between

Umuezejor and Ugbaike. Resistivity variation at the

subsurface depends on a number of factors, viz, lithology,

porosity and permeability, stratification, fluid content

and quality, and heat condition of the rock. The higher 4

the porosity and permeability, water content and salinity

and the metallic mineral content of a particular rock type,

the lesser its resistivity. High temperature increases the

concentration of electrons in semi-conductors (such as

rocks) and thus raises the electrical conductivity of rocks

(Rzhevsky and Novik, 1971). If the rock layers have a

steep dip and resistivity measurement is made perpendicular

to strike, the apparent resistivity will be smaller than

the true resistivity normal to the bedding. If the array

is parallel to the strike of the dipping beds, the apparent

resistivity will be too large (Telford et al, 1976).

Depth of investigation is variable too, and is

dependent on relative conductivity and thicknesses of the

subsurface geological strata, lateral variations in the

electrical properties and thicknesses of the component

layers; and subsurface or near-surface irregularities.

Surface geologic mapping of the area and the environs,

petrographic studies of the component formations, such as

by Hoque and Ezepue (1977); and lithologic logs all support

the presence of all the above factors, hence variation of b

the depths of investigation and layer resistivities at the

different stations is justified.

Variation in the layer resistivities is attributed to

grain size variations (medium to coarse), degree of

ferruginisation and lateritization, intensity of fracturing

and water saturation. Degree of water saturation was most

probably responsible for the very low surface resistivity

values at Iheakpu and Iheaka on the one hand, and the high

values at Umusigide on the other. While the former areas

were well watered by rain before the soundings, the latter

was dry. The high values of resistivity (113, 115.81 - 699, 663.38 Ohm-m) at depths between 31.0m and 80.0m are

attributed to the coarsening downwards of the sandstone,

and very low water content at depths above the water table

(static water level varies from 101.0m at Ovoko to 113.0m

at Ugbaike, according to 1977 borehole record).

A comparison of the borehole logs of the study area (Figs.

8 and 9) reveals that the lithology is basically the same,

although some rock units appear to be lost in some places,

and layer thicknesses vary. The lithology is thought to

have a low range of primary porosity values, and does not

seem to allow for the wide changes in resistivity observed Some

atAdepths. Moreover, the dip of the Ajali Sandstone range

from 3O to 7O. Consequently, the lithology and

stratification appears to contribute very little to the b

observed vertical variation in the ground resistivity. It

is, therefore suspected that the vertical variation is due

mainly to the degree of fracturing and water saturation at

the different stations.

4.2.2 ELECTRICAL ANISOTROPY

Figures 10.1 - 10.7(lpg~,45-55) are anisotropy

diagrams plotted with apparent resistivities against AB/2

along both sounding traverses at each station. Such

diagrams are often used to express the degree and attitude

of electrical anisotropy (such as that due to fracturing)

of rock formations (Mallik et all 1983; Mamah and Ekine,

1989). Mallik et a1 (1983) observed that the apparent

resistivity of any anisotropic formation due to the

presence of fractures measured normal to its strike

direction is less than that measured along the strike

direction.

GEOLOGICAL SURVEY W NIGERIA

a Shale El Sandstone

Weathered sandstone Weathered sandy shale Weathered grit

a Carbonaceosdde B9 Weathered shale = Coal I

Blank parts of sectiorl i n d i t e nosludge or core recovery

VERTICAL SCALE: tin = Soft

FIG. 8 BOREHOLE SECTIONS AT EZIMO (courtesy of Geological Survey of N ig eria)

For an homogeneous and isotropic medium, the component

quadrilaterals (or polygons, in case of more than two

azimuths) of the anisotropy diagrams have circular shape.

Any tendency towards elliptical form indicates electrical

anisotropy of the formation. The degree of anisotropy

designated as coefficient of apparent anisotropy ( Aa), is

calculated from each elliptical quadrilateral (or polygon)

by the relation Aa = a/b, where a and b are the semi-major

and semi-minor axis respectively of the ellipse fitted +

through each quadrilateral. For the homogeneous and

isotropic medium A a = 1 (Tables 5,Pgs. 120-326) . Figures

10.1 - 10.7 are thus interpreted to show the attitudes and degrees of fracturing of the formation at each station at

various depths corresponding to different electrode

separations.

According to Mallik et a1 (1983) the strike direction

of the anisotropy is given by the major axis of the ellipse

which can fit the quadrilateral. The above observation is,

however, not true for all cases of rock fractures.

Apparent resistivity measured along the strike of fracture

is less than that measured normal to it when the fracture

is water-saturated or filled with some other conductive

materials (Hardt, 1984; Brace and Orange, 1968; Stesky,

1986; Walsh and Brace 1984).

This is explained by the fact that such conductive

materials within the fracture increases current flow along

the strike of the fracture. Thus, the strike direction of

the fracture is given by either the major axis or minor

axis of the ellipse depending on the materials filling the

fracture. In this thesis, both the major and minor axis of

the ellipse are interpreted as supporting fracturing in two

perpendicular or almost perpendicular directions, one being

more pronounced than the other. In plotting the curves, +

points of little or no anisotropy, and of maximum

anisotropy were selected. AB/2 was limited to 0-150m as

this presents the whole picture of the ground anisotropy in

the area of study.

At the boundary between Umuezejor and Ugbaike the

quadrilaterals all tend to circular outline (Fig. 10.la).

Values of Aa range between 1.0 and 1.12 suggesting that the

region is very homogeneous (Table 6) with low intensity of

fractures.

At Ugbaike, a similar trend is observed (Fig. 10.2a).

There are high values of apparent resistivity first along

the 125' azimuth (NW - SE) from the surface down to a depth corresponding to AB/2 = 5.3m, then a reversal to

0 30 azimuth (NE-SW) to a depth corresponding to AB/2 =

15m, and finally a trend in the NW-SE direction.

FIG. 10.1 (a ANISOTROPY DIAGRAM SHOWING THE DIRECTIONS OF FRACTURING I N UMUEZE JOfUUGBAIKE BOUNDARY.

(b) VARIATION OF THE DEGREE OF FRACTURING WITH DEPTH.

TABLE 6 CLASSIFICATION OF DEGREE OF HOMOGENEITY (after

Mamah and Ekine, 1989)

COEFFICIENT OF ANISOTROPY CLASSIFICATION

------------- 3-------- Very homogeneous -A

Homogeneous -B ...................... Fairly Homogeneous -C ...................... Heterogeneous - D

ABf2 45 - ( m l

60 -

75 - 90 - SCALE :

Horizontal , , 01 UplT (bl J i

105 - Vertical - tk4 I

'4 1

FIG.10.2 (a) ANISOTROPY DIAGRAM SHOWING THE DIRECTIONS OF FRACTURING IN UGBAIKE.

(b) VARIATION OF DEGREE OF FRACTURING WITH DEPTH .

Geoelectric sounding was carried out at this station after

about the first two rains which wetted the surface layer,

leaving the middle zone dry. Fractures thus appear to be

persistently more prominent in the NE-SW direction(minor

axis at the wetted surface and deep layers, major axis at

the intermediate layers) . Values of j\ a (between 1.3 5 ,and

2.0, table 5.2, fig. 10.2b) depicts very heterogeneous

medium at depths equivalent to AB/2 = 25m. The above

result agrees with surface observations. +

At Umuezejor (Fig 10.3) the top layer corresponding to

AB/2 = 0.32 - 1.5m has low resistivities (952 - 1002 Ohm-m) along 30' azimuth compared to 120' azimuth. From a

depth corresponding to AB/2 = 3.0m downwards apparent resistivity along the 30' azimuth attains consistently

and remarkably higher values (Table 5.3). The initial

rains that wetted the surface layer must have left dry the

layers below. The result is, thus, interpreted to show a

more pronounced anisotropy along the N-S to NNE-SSW

direction. Values of Aa between 1.0 and 1.24 suggest a

very homogeneous to homogeneus formation at the station,

and a low degree of fracturing, or low intensity difference

in fracturing along both directions in the deeper layers.

FIG.10-3(a) ANISOTROPY DIAGRAM SHOWING THE DIRECTIONS OF FRACTURING IN UMUEZEJOR

(b) VARIATION OF THE DEGREE OF FRACTURING WITH DEPTH

Similarly, at Iheakpu the minor axis along 75 0

azimuth (Fig. 10.4) gives the direction of the probable

major fracture. This traverse was well watered by

rain before the sounding in contrast to the hardened foot

path and football field which constituted the 165'

azimuth. The values of Aa here (1.18 - 1.83) are indicative of very heterogeneous medium, and probably high

intensity of fracturing at the surface (along the ENE-WSW

to E-W directions) which gradually decays into an B

homogeneous medium below depths equivalent to AB/2 = 100m.

The NNE-SSW traverse at Iheaka (Fig. 10.5) was a

highly consolidated road, while the WNW - ESE traverse was 1

a soft farmland. The low apparent resistivity at the

surface of the former, and higher values from depths

equivalent to AB/2 > 8.0m could be indicative of higher

intensity of fractures in the NNE-SSW trend. The ground

here, excepting the surface layers, appears to be very

homogeneous. This agrees with surface observations.

The contrary is the case in Ohulor (Fig. 10.6). Here,

the ground appears to be homogeneous except at depths

corresponding to AB/2 > 100m. Fracturing appears to be

almost of equal intensity in both N-S and E-W directions.

FIG.?O-4(a AN1 SOTROPY DIAGRAM SHOWING THE DIRECTIONS OF FRACTURING IN IHEAKPU


FIG1 O.S(a) ANISOTROPY DIAGRAM SHOWING THE DIRECTIONS OF FRACTURING IN IHEAKA

(b) VARIATION1 OF THE DEGREE OF FRACTURING WITH DEPTH.

Xa 1.0 1;1 1.J li3 0

15-

30- AW2

(m) 45- p 1 uyn

60

75-

90

100

-

Vertical ,15m,

- f (b,

FIG. lO6a ANISOTROPY DIAGRAM SHOWING THE DIRECTIONS OF FRACTURING IN UMUSIGDE

(b)VARIATlON OF THE DEGREE OF FRACTURING WITH DEPTH

At Umusigide (Fig. 10.7) the high values of apparent

resistivity, and values offla between 1.0 and 1.06 almost

throughout the entire depth range depicts high degree of

fracturing, but of almost equal intensity in the directions

of measurement.

In general, the observations show that there is

variation in the directions of fracturing across the

stations from N-S /NE-SW trend through E-W to NW-SE trend,

and fluctuations in the intensity of fracture with depth.

Thus, the continuity of the surface fractures into the

subsurface, and their orientations in the N-S to NE-SW,

through E-W to NW-SE directions are strongly supported by

the VES result.

4 . 2 . 3 CAUSE OF FRACTURING

Fractures at the earthts surface nd buildings may be

caused by stress in the subsurface which results in the

rupturing of the rocks when the strength of the latter is

exceeded. Such rupturing of rocks in the earth's crust

often occur, not along a single line or over a single spot,

but on a regional scale over a network of lines, such as is

observed in the area of study.

FIG.

. I

55

1.0 11 12 1.3 1 4 I 'p (01

0.1 UNIT Scale: Horizontal - , vertical - ?-

AB12 45

75 :\ 105 \

\ \

10.76) ANISOTROPY DIAGRAM SHOWING THE DIRECTIONS OF FRACTURING IN OHULOR


1 Scale: Horizontal - ,

ash uth

10.76) ANISOTROPY DIAGRAM SHOWING THE DIRECTIONS OF FRACTURING IN OHULOR

Seismic and quarry (rock - blasting) activities, and earth-quakes could produce fractures both in the ground and

on buildings. I1Cracks in the walls of buildings," such as

in Plate 2, may also be caused by "differential settlement

due to poor foundation designs in soft soil condition^^^

(Fubara, 1990). Other causes of fracturing includes

faulting, tectonic event, and cavity development in the

sub-surface due to ground water solution (Orazurike, 1987).

A careful observation of the fractures shows that b

there is no vertical displacement of the walls of the

fractures. Lateral displacements are, however, conspic ous Lw h n

as gaps (of widths ranging from,Imm to4Omm in the

majority) in houses all over the study area which widen

from the floor of those houses to their highest value at

the top of the walls. Some inhabitants of Ugbaike,

Umuezejor and Ohulor have reported opening of the ground at

some points along the fracture traces some time in the past

during extreme dry weather conditions. These openings,

they said, could take a stick as long as seven feet (7ft)

or more. Though the openings have been closed by rainwash,

the fracture lines are still traceable. It is still

doubtful, nevertheless, whether these openings are true

lateral displacements characteristic of faulting.

Of the total thickness of 330m' of Ajali Sandstone,

over 200m (including the red earth cover) has been

confirmed from borehole logs (Courtesy of Anambra State

Water Corporation). Sub-surface geology consists of thick

layers of Sandstone and gravels, and few thin layers of

clay at great depths. This lithology has no suggestion of

such softness, or ground water solution that could trigger

off ground collapse and the consequent fracturing. Neither

seismic/quarry

scale has been

the fractures,

operations, nor earthquake

reported in the area. The

lack of lateral continuity

occurrence of any b

small widths of

over distances

greater than few metres, and lack of obvious displacements

of the fracture walls (characteristic of faulting) cast

doubts on faulting as the cause of fracturing of the area.

From the above discussions, we are left with two

options, viz, tectonic event(s) and drastic climatic

fluctuations as the probable causes of the fracturing.

Tension cracks are common in areas underlain by clay,

shales and other such fissile materials, and are well known

to be products of severe heat during dry seasons. Such

cracks differ from the ones in this study area in that they

lack well defined orientations, and (except those in

buildings and concrete floors) close almost entirely during

rains.

Fractures of the scale in this area are not known to the

author to have climatic changes as the primary cause.

Nevertheless, the nature of the fractures is obviously

characteristic of tensional pulls in the rocks which tend

to open and close during the dry and wet seasons

respectively; The author, thus supposes that fracturing in

Obollo Afor area is an after effect of the upliftment of

the area during the Miocene-Pliocene period, accelerated by

the drastic atmospheric changes between the dry and wet 4

seasons. It can not be a product of Santonian tectonic

episode as Unuevho (1983) thought, since the stratigraphic

sequence underlying the area of study is only Maastrichtian

to Danian in age. This could, however be a contributing

factor if a resurgence of the event is established.

CHAPTER 5 SUMMARY AND CONCLUSION

Obollo Afor area, as defined here is a part of Anambra

basin of Nigeria and is underlain predominantly by

furruginised sandstone and loose to poorly consolidated

sandstones and gravels of Ajali Sandstone. Underneath it

lies the sandstones, shales and mudstones of Mamu Formation

at some depths. The entire area is highly fractured in two

perpendicular or almost perpendicular directions, the

fractures trending either NE-SW and NW-SE or N-S and E - W

with deviations to NNE-SSW and ESE-WNW directions. * Radial geoelectric sounding (VES) was carried out at

seven locations in the area at the beginning of the rainy

season (1990). The field observations were analysed through

a direct computer interpretation programme, and

coefficients of anisotropy were calculated for all the

stations and interpreted in terms of degree of fracturing

and water saturation. The sounding data confirm fracturing

in two principal directions in each locality as observed at

the surface, and indicates variable intensity of fracturing

with depth.

There is a good csrrelat%on between fracture

orientations, erosion gullies and stream channels. This is

suggestive of a common origin of the structures, and

specifically that the gullies and streams followed

pre-existing fractures. The definite orientation of the

fractures, coupled with their persistence over the entire

area, and the opening and closing of the fractures during

dry and wet seasons suggest that the fracturing was

initiated by a tectonic episode and activated by the B

harsh climate changes between the dry and wet seasons in

the area. Lack of obvious displacements of the walls of the

fractures is an indication that the fractures have little

or no bearing with faulting, while the continuous

fracturing of recently built houses is indicative of the

activity of the tensional forces that cause them. It is,

therefore, suggested that more research be carried out in

the area with the aim of determining the growth rate of the

fractures and gullies and any other structural development

in the area. This, the author believes, will enhance an

unambiqous determination of the cause(s) of fracturing and

possible solutions to the problem.

REFERENCES

Bain, A.D.N. 1924. The Nigerian coal field, Enugu Area Geol. Surv. Nigeria Bull., No.6,~

Banerjee, I. 1979. Analysis of cross-bedded sequence, an example from the Ajali Sandstone of Nigeria. Quart. Geol. Min. Metal. Soc. India, V.51(2), p.69-81.

Brace, W. F..and orange, A. S. 1968a-Electrical resistivity changes in saturated rocks during fracture and frictional sliding. J. Geophys. Res., v.73, p.1433-1445.

De Swardt, A.M.J. and Casey, O.P. 1963. The coal resources of Nigeria. Geol. Surv. Nigeria Bull., No. 28, p.

@ Egboka, B.C.E. 1983. Analysis40f the groundwater resources

of Nsukka area and the environs. Nigeria J. Min. and Geol., v.20, p 1-6.

Egboxa, B.C.E. and Nwankwor, G.I. 1985. The hydrogeological and geotechnical parameters as agents for gully-type erosion in the rain forest belt of Nigeria. J. African Earth Sci., v.3, p.417-425.

Floyd, B. 1965. Soil Erosion and deterioration in Eastern Nigeria. Nigerian Geogr. J., v.8, p.33-43.

Fubara, 1990. VictQria Island is not under threat. The Guardian, Thursday, February 1, 1990, p.1.

Ghosh, D. P. 1971a. The application of linear filter theory to the direct interpretation of geoelectrical resistivity sounding measurements. Geophy. Prosp. (Netherlands), v.11, No.4, p.471-508.

Grove, A.T. 1951. Land use and soil conservation in parts of Onitsha and Owerri Provinces. Geol. Surv. Nigeria Bull., v.21, p.5-28.

Hardt, I.

Hoque, M.

Hoque, M.

Hoque, M.

1984. A geoelectrical frac detection method. Natural Resources and Development, v.19, p.43-50.

1976. Significance of the textural and petrographic attributes of several Cretaceous sandstones, Southeastern Nigeria. J. Geol. Soc. India, v.17, p. 514-521-

1977. Petrographic differentiation of tectonically controlled Cretaceous sedimentary cycles, Southeastern Nigeria. Sedim. Geol., v.17, p. 235-245.

and Ezepue, M.C. 1977. Petrology and Paleogeography of the Ajali sandstone. Nigerian J. Min. Geol. v.14(1), p. 16-22.

4 Koefoed, 0. 1979. Geosounding principles, 1:

Resistivity sounding measurement. Elsevier Scientific Publication Company, Amsterdam. p. 141-215.

Mallik, S. B., Bhattacharya, D.C. and Nag, S.K. 1983. Behaviour of fractures in hard rocks - a study by surface geology and radial VES method. Geoexploration, v.21(3), p.181-189.

Mamah, L.I. and Ekine, A.S. 1989. Electrical resistivity anisotropy as indicator of sedimentary fabric resulting from tectonic adjustments in basal Nsukka Formation. Nigerian J. Min. and Geol., v-25, ~.f21-129.

Nwachukwu, S.O. 1972. The Tectonic evolution of the Southern part of the Benue trough. Nigerian Geol. Mag., v. 109, P. 411-419.

Nwajide, C.A. and Hoque, M.1979. Gullying processes in Southern Nigeria. Nigeria Field, v.XLlV, p.64-74.

Ofomata, G.E.K. 1965. Factors of soil erosion in the Enugu area of Nigeria. Nigeria Geogr. J., v.8, p.45-59.

Ogbukagu, IK. N., 1976. Soil erosion in the northern part of the Awka - Orlu uplands; Nigeria Geogr. J., v.8, p.45-59.

Okagbue, C. 0. 1986. Gully development and advance in a rain forest of Nigeria. 5th International IAEG Congress/Buenos AIRES 1986, p.1999-2009.

Orazulike, D. M. 1987. Recent cracks in the vicinity of Pindiga,Bauchi state: product of groundwater solution. Nigeria J. Min. Geol., v.23, Nos. 1, 2, p.105-108.

Ozoko, D.C. 1988. The hydrogeology of Nsukka area and environs, Anambra State, Nigeria. Unpublished M.Sc. thesis, University of Nigeria, Nsukka.

Reyment, R.A. 1965. Aspect of the geology of Nigeria. Ibadan University Press, Ibadan.

Short, K.C. and Stauble, A. J. 1967. Outline of geology of the Niger Delta. Bull. A. A. P.G., v.51, , p.761-779.

Simpson, A. 1954. The Nigeria coalfield: The geology of parts of Onitsha, Owerri and Benue Provinces. Geol. Surv. Nigeria Bull., No. 24, p.1-85.

Stesky, R.M.1986. Electrical conductivity of brine saturated fractured rocks. Geophysics. v.51, No.8, P.1585-1593.

Sunde, E.D. 1944. Earth conduction effects in transmission systems. New York, Van Rostrand, 370 P-

Tattam, C. M. 1944. A review of Nigerian stratigrphy. Geol. Surv. Nigeria Ann. Report, p.27-46.

Technosynesis, SP. A. 1978. Soil erosion control in Imo and Anambra States, part 1, control measures against gully erosion. Technical report prepared for the Federal Ministry of Agriculture and Rural Development of Nigeria.

Telford, W.M., Geldart, L.P, Sherrif, R.E and Keys, D. A. 1976. Applied geophysics. Cambridge University Press, London

Uma, K. 0. and Onuoha, K. M. 1986. Groundwater fluxes and gully development in Southeastern Nigeria. Groundwater and Mineral Resources of Nigeria. p.39-59.

Unuevho, C. I. 1983. Geology of the area northwest of Igumale, Udenu and Okpowu Local Government areas, Anambra State and Benue States respectively, Nigeria. Unpublished B.Sc. thesis, University of Nigeria, Nsukka.

Walsh, J. B. and Brace, W.F. 1984. The effect of pressure on porosity and transport properties of rock. J. Geophys. Res., v.89, p.9425-9431.

Zohdy, A. A.R. 1975. Automatic interpretation of Schlumberger sounding curves using modified Dar Zarrouk functions. Geol . Surv. Bull ; l313-&-.

APPENDIX 1 - TABLES 3.1 - 3.7 - OBSERVED RESISTIVITY SOUNDING RESULTS

TABLE 3.la OBSERVED RESISTIVITY SOUNDING RESULT LOCATION: Umuezejor@Jgbaike boundarg. COORDINATES: Longo7 30.gfE, Lat. 6 AZIMUTH OF AB: 40 Date: 23/4/90

OBSERVED GROUND

RESISTANCE R( ohm )

m) 1 SMOOTHED . 1 CURVE

.............................................................. EXPLANATION :

AB/2 = current electrode spacing (in metres)

MN/2 = potential electrode spacing (in metres)

R = observed ground resistance (in ohm)

F = fingeometric factor" of & (in metre)

_& = apparent resistivity (in ohm-metre)

g(2) = resistivity of smoothed curve (in ohm-metre)

TABLE 3.lb OBSERVED RESISTIVITY SOUNDING RESULT

LOOATI COORDI AZIMUT

Umuezeaor/Ugbaike bounaary. YATES : Long 7 30.gtE, Lat. 6 55.5'N 3 OF AB: 130 Date: 23/4/90

OBSERVED GROUND

RESISTANCE R( ohm )

.B/2 RESISTIVITY OF (m) 1 OF SMOOTHED

CURVE

&I MM-~?)

5 35 205.2133 7,182.47 150 21,000 5 25 339.2920 8,482.30 180 23,000 5 18 609.1324 10,964.38 200 25,000 0 14 15 1100.0062 16,500.09 0 6.1 2502.5029 15,265.27 0 4.1 4466.0 18,310.60 ..............................................................

EXPLANATION: : AB/2 = current electrode spacing (in metres)



F = "geometric factornn of (in metre)

94 = apparent resistivity (in ohm-metre)

f4z) = resistivity of smoothed curve (in ohm-metre)

TABLE 3.2a OBSERVED RESISTIVITY SOUNDING RESULT LOCATION: Ugbaike COORDINATES: Long 7 0 3 0 . 8 r E , Lat. 6' 5 5 . g r N

AZIMUTH OF AB: 30 Date: 24/4/90 .............................................................. R F s.

( ohm-m) Slaw

( ohm 1 (ohm-m)

EXPLANATION -: AB/2 = current electrode spacing (in metres)



F = "geometric factortt of fa (in metre)

% = apparent resistivity (in ohm-metre)

!&(2)= resistivity of smoothed curve (in ohm-metre)

TABLE 3.2b OBSERVED RESISTIVITY SOUNDING RESULT LOCATION: Ugbaike COORDINATES: bong7 30.8'E, Lat. 6'55.9'N AZIMUTH: 125 Date: 24/4/90

.............................................................. R F AB/2 fa(2)

(m) (ohm-m)

EXPLANATION : AB/2 = current electrode spacing (in metres)



F = ttgeometric factorvv of & (in metre) fi = apparent resistivity (in ohm-metre)

&(2) = resistivity of smoothed curve (in ohm-metre)

TABLE 3.3a OBSERVED RESISTIVITY SOUNDING RESULT LOCATION : Ugbaikg 0 COORDINATES: Lotjg.7 30.3?EI Lat. 6 55.3'N AZIMUTH : 30 Date: 24/4/90




F = 'geometric factoru of (in metre)

= apparent resistivity (in ohm-metre)

f~1)= resistivity of smoothed curve (in ohm-metre)

TABLE 3.3b OBSERVED RESISTIVITY SOUNDING RESULT LOCATION: Umueze or d 0 COORDINATES: Lo~g. 7 30.3'E, Lat. 6 55.3'N AZIMUTH : 120 Date: 1/5/90 ..............................................................

R F fa



F = ttgeometric factornn of % (in metre)

1.5 3 6 8 10 15

10 15 20 25 35 45 55

45 55 75 100 150 180 200


FXPLANATION : AB/2 = current electrode spacing (in metres)

&Q = resistivity of smoothed curve (in ohm-metre)

0.5

3.5

14

............................................................. 6.2832

27.4889 112.3119 200.2765 313.3739 706.0729

39.3821 95.4820 174.0218 275.0016 544.2809 903.3201 1352.120 ............................................................. 205.2133 339.2920 609.1324 1100.0062 2502.5029 3613.2804 4466.0 ..............................................................

1.5 3 6 8 10 15

20 25 35 45 55 75 100

215 42 16 11 8 6 .............................................

87 30 20 13 10 8 7

28 22 13 12

4.4 3.6 3.1

1350.89 1154.53 1796.99 2203.04 2506.99 4236.44

3426.24 2864.46 3480.44 3575.02 5442.81 7226.56 9464.84

5745.97 7464.42

17918.72 13,200.07 11.011.01 13,007.81 13,844.60

1,050 850

1,300 1,550 1,800 3,000

3,400 3,800

fi 5,400 7,200 9,500 10,000 14,000 iL! 25,000 , 32,000 38 000

EXPLANATION' : AB/2 = current electrode spacing (in metres)



F = 'geometric factorn of (in metre)

Sb = apparent resistivity (in ohm-metre)

fi@) = resistivity of smoothed curve (in ohm-metre)

TABLE 3.4b OBSERVED RESISTIVITY SOUNDING RESULT LOCATION: Iheakp~ COORDINATES: Loflg.7 29.7IE, Lat. 6'54.6'N AZIMUTH : 165 Date: 1/5/90

Pa AB/ 2 (ohm-m) (m)

EXPLANATIONS: AB/2 = current electrode spacing (in metres)



F = "geometric factorww of .f& (in metre)

& = apparent resistivity (in ohm-metre)

%(I) = resistivity of smoothed curve (in ohm-metre)

TABLE 3.5a OBSERVED RESISTIVITY SOUNDING RESULT LOCATION: Iheakao (Likke) COORDINATES: Losg 7 29.0 E l Lat. 6' 53.8 IN AZIMUTH : 22 Date: 2/5/90

XPLANAT ION' : AB/2 = current electrode spacing (in metres)



F = "geometric factorw of % (in metre)

& = apparent resistivity (in ohm-metre)

&[t)= resistivity of smoothed curve (in ohm-metre)

.............................................................. EXPLANATION :

AB/2 = current electrode spacing (in metres)



F = "geometric factorH of (in metre)

$I = apparent resistivity (in ohm-metre)

9b($ = resistivity of smoothed curve (in ohm-metre)

TABLE 3.6a OBSERVED RESISTIVITY SOUNDING RESULT LOCATION: Umusigade 0 COORDINATES: Loeg-7 33.5'Et Lat. 6 53.7'N AZIMUTH : 16 Date: 5/5/90




F = llgeometric factortt of Pa (in metre)




TABLE 3.6b OBSERVED RESISTIVITY SOUNDING RESULT LOCATION: Umusigade COORDINATES: L o p 7 33.5)E, Lat. 6'53.7)N AZIMUTH : 106 Date: 5/5/90


F = "geometric factorl1 of .% (in metre)

$ = apparent resistivity (in ohm-metre)

a(1) = resistivity of smoothed curve (in ohm-metre)

AB/2 (m)

1.5 3 6 8 10 15

10 15 20 25 35 45 55

45 55 75 100 150 180 200


.............................................................. F (m)

............................................................. 6.2832

27.4889 112.3119 200.2765 313.3739 706.0729

39.3821 95.4820 174.0218 275.0016 544.2809 903.3201 1352.120

205.2133 339.2920 609.1324 1100.0062 2502.5029 3613.2804 4466.0 ..............................................................

MN/2 (m)

0.5 .

3.5

14

fa (ohm-m)

2544.70 3573.56 4941.71 7209.95 7207.60 8472.87

7010.01 7161.15 6438.81 5775.03 5987.09 7226.56 9464.84

4514.69 4750.09 6091.32 7700.04 27,527.53 25,292.96 26,796.0

R (ohm)

405 130 44 36 23 12 .............................................

178 75 37 21 11 8 7 .............................................

22 14 10 7 11 7 6

AB/ 2 (m)

1.5 3 6 8 10 15

20 25 35 45 55 75 100

150 1180 200

fh (ohm-m)

2,500 3,600 5,000 7,200 7,200 7,200

6,400 5,800

) 6,000 7,200 8,500 11,800 17,000

37,000 52,000 55,000

TABLE 3.7a OBSERVED RESISTIVITY SOUNDING RESULT LOCATION: OhulorO COORDINATES: L o p 7 30.gfE, Lat. 6'54.5'N AZIMUTH : 10 Date: 5/5/90




F = I1geometric factoru of $ (in metre)

yfi = apparent resistivity (in ohm-metre)


TABLE 3.7b OBSERVED RESISTIVITY SOUNDING RESULT LOCATION: OhulorO COORDINATES: Loeg.7 30.9'E1 Lat. 6'54.5'N AZIMUTH : 100 Date: 5/5/90




F = !!geometric factortt of & (in metre)

fa = apparent resistivity (in ohm-metre)

f4(2)= resistivity of smoothed curve (in ohm-metre).

APPENDIX 2 - FIGURES 5.1 - 5.7 - OBSERVED RESISTIVITY SOUNDING PROFILES

smoothed

E L E C T R O D E S P A C I N G , A 8 / 2 ( m )

F IG. 5 .10 : OBSERVED R E S I S T I V I T Y P R O F I L E , U M U E Z E J O R /

UGBAIKE B O U N D A R Y , on^. 7 ' 3 0 . g 1 € , L o t . 6" 5 5 - 5 ' ~ ) V E S 40" o z i r n u t h , 2 3 / 4 / 9 0

- 2-

smoothed

-

10'. observed 9- ,X

7- x '

4-

3 - - 2 -

I o~~ 1 -8

I I I I I I I I I I I I I 1 I I I I I I I I I I

I 2 3 4 5 6 7 8 9 1 0 2 3 4 5 678910 ' 1.5 2 x 1 0 ~

E L E C T R O D E S P A C I N G , A B / 2 ( m )

FIG.5 . lb : OBSERVED RESlSTlVlTY PROFILE, UMUEZEJOR UGBAIKE,

Long. 7'30.9'€, L o t . 6'55.5' N., 40' azimuth, 23/4/ 90


F l C . 5 . 2 0 : OBSERVED RESISTIVITY PROFILE, UGBAIKE-, Long. 7 O 30.8' E , Lot . 6' 55 - 9 ' ~ ,30° a t imu th, 2 4 / 4 / 9 0

E L E C T R O D E S P A C I N G , A B / 2 (m )

F I G . 5 . 2 b : OBSERVED R E S l S T I V I T Y P R O F I L E , U G B A I K E ; Locg. 7030.8'~

Lot. 6 * 5 5 * ' 9 ' ~ , 125O a z i m u t h , 2 4 / 4 / 9 0 .

9 x 1 0 t 8 - 7 - 6- 5-

4- C-

3 - i z 2. 2 - s m o o t h e d

,/ x '

0 f 4 - > I- 18- - 9-

\/-I' 8- v, - 7-

/x

v, 6- W

~ " t ,x' O b s e r v e d

a g-

I- 4- observed /

z w 3- rK a a a 2- a -

3 10-

2 9- 1-8

ELECTRODE SPACl NG , A B / 2 ( m )

FIG. 5. 30 : O B S E R E D R E S I S T I V I T Y P R O F I L E , U M U E Z E J O R ; L o n g . P 3 0 . 3 ' ~ , L o t . 60 55.3'N, 30° o z i m u t h , 1 / 5 / 9 0

ELECTRODE S P A C I h i G , A B / 2 ( m )

F I G . 5.3 b : OBSERVED RESISTIVITY PROFILE , U M U E Z E J O R ; Long. 7 " 3 0 . 3 ' , ~ a i . 7 ~ 5 5 - 3 ' ~ , I Z O O a z i m u t h ,

1 / 5 / 9 0

' observed


FIG.5.4 o : O B S E R V E D R E S I S T I V I T Y P R O F I L E , IHEAKPU; L o n g . 7' 2 9 . 7 ' ~ ~ L o t . 6054.6' N ,

75' a z i m u t h , 11 5 1 9 0 .

I 2 3 4 5 6 7 8910 2 3 - 4 - 2 678910 ' 1.5 2x10'

E L E C T R O D E S P A C I N G , A B I 2 ( m )

FIG. 5 . 4 b : OBSERVED RESISTIV ITY PROFILE, IHEAKPU ; Long. 7' 2 9 . 7 ' ~ ; L a t . 6O45 -6' N ; 165O azimuth,

I / 5 I 9 0

/ x

X /

o b s e r v e d / x o b s e r v e d

- - - - - - ----- 2- 3 4 5 6 7 8 9 K ) 2 3 4 5 6 78910' 1-5 2x10' . . _ELECTRODE S P A C I N G , A B / 2 ( m )

FIG. 5 . 5 0 : OBSERVED RESISTIVITY PROFILE, IHEAKA(LIKKEI, ~ o n g . 7 0 2 9 . 0 ' ~ , L a t . 6 O 53.8'~, 22"azimuth,

I 2 3 4 5 6 78910 2 3 4 5 6 7 8 9 1 0 ~ 1.5 2x10'


F I G . 5.5 b : O G S E R V E D R E S I S T I V I T Y P R O F I L E , I H E A K A (L IKKE) , L o n g . 7 * 2 9 . 0 ' ~ , ~ 0 1 . 6 0 5 3 . 8 ' ~ ;

115' a z i m u t h , 5 1 5 1 9 0 .

ELECTRODE SPACING, AB /2 ( m )

FIG. 5 - 6 0 : OBSERVED RESISTIVITY P R O F I L E ,

UMUSIGIDE, L o n g , 7" 3 3 . 5 ' E, Lot. 6" 5 3 . 7 ' N ,

1 6 O a z i m u t h , 51 5 / 9 0 .

E L E C T R O D E S - P A C I N G , A B / 2 ( m )

FIG. 5 a 6 b : OBSERVED RESISTIVI.TY. PROFILE,_UMU-St-GI-D_E_ ,----- Long. 7" 3 3 . 5 ' ~ , L o t . 6 " 5 3 . 7 ' ~ ; 106O o z i muth,

5 1 5 1 9 0

Observed \

smoothed

I 2 3 4 5 678910 2 3 4 5 6 7 8 9 1 0 ~ ; 5 2x10'


FIG: 5 . 7 0 : OBSERVED RESISTIVITY P R O F I L E , OHULOR ; L o n g . 7 ' 3 3 . 5 ' ~ , L o t . 6" 53.7'~; l o0 azimuth, 5 / 5 / 9 0

I 04x 4

3 - - - 2-

E

i - C 0 CI

q 6- >- g t > - F 6 - V) - 5- V)

: 4-

l- 3- 2 - W e 2- Q n n u

13 ) I f I I 1 1 1 1 1 q I , s I I , I I t , , , , - I 2 3 4 5 6 7 8 9 1 0 2 3 4 5 6 7 8 9 1 0 2

E L E C T R O D E S P A C r N G , A 8 1 2 (-mi

FIG. 5 . 7 b : OBSERVED RESISTIVITY P R O F I L E , OHULOR; L o n g . 7" 3 3 . 5 ' ~ ) L o t . 6 O 5 3 . 7 ' ~ i

100" a z i m u t h , 5 / 5 / 9 0

APPENDIX 3 - TABLES 4 . l a - 4.76 - DIRECT INTERPRETATION

RESULTS

TABLE 4m?a DIRECT INTERPRETATION RESULT

LOCATION: umuezejor/ugbaike boundary

COORDINATES: Longe 7O 3 0 . 9 * ~ , ate 6O 5Se5@N

AZIMUTH OF AB; 40° DATE : 23/4/90

REDUCED THICKNES:

(m)

Oe58

om22

0.08

0.67

4.36

4m46

3 m80

lm5O

2m34

2m97

5,76

14m55

19m67

38,03

1.3 l 79

REDUCED DEPTH

(m)

Oe58

O m 8 O

0m88

1,55

5,90

10m36

14,16

15m67

18m01

20m98

26,74

41m29

60m96

98m99

12.78

REDUCED RESISTIVITY

( ohm-m 1

TABLE 4.lb DIRECT INTERPRETATION RESULT

LOCATION: umueze jor /ugbaike boundary 0

COORDINATES: Long. 7 3 0 . 6 1 ~ , L a t e 6O 5 5 . 5 1 ~

AZIMUTH OF AB: 130°

REDUCED THICKNESS

( m )

REDUCED DEPTH

( m )

DATE: 23/4/90

REDUCED RESISTIVITI

( ohm-m )

- CALC oVES

( ohm-m )

1836.60

1843.91

1860.37

1902.89

2018.92

2290.99

2783 a27

4139.66

5554.74

5906058

6075 a56

59774.13

6080.11

6467.29

7755.42

9263.23

10744.24

13417.04

16273.95

21117.66

23 769 e48 25482.54

1

OBSERVED f VES

(ohm-m)

TI~BLE 4 e 2eL DIRECT INTERPRETATION RESULT-

LOCATION : u g b a i k e

COORDINATES: Long. 7O 30.81~, at. 6O 55.911

AZIMUTH OF AB: 30' DATE : 24/4 /9Q - REDUCED THICKNESS

( m )

REDUCED DEPTH

( m 1

REDUCED I A B / ~ t RESISTIVITY

( ohm-m 1 ( m ) -

I 1385 .42 , I

I

OBSERVED

( ohm-m 1

TABLE 402% DIRECT INTERPRETATION RESULT

LOCATION : u g b a i k e

0 0 COORDINATES : ~ o n g . 7 3 0 . 8 , ~ , L a t o 6 5 5 . 9 , ~

REDUCED THICKNESS

( m )

?-EDUCED DEPTH

( m )

DATE : -

EDUCED E S I S T I V I T Y

( ohm-m )

A B / ~ CALC. VES OBSERVED

( m ) ( o h m a ) t '

-

1

3

2

TABLE 403a DIRECT INTERPRETATION RESULT

LOCATION : umueze jor

COORDINATES : ~ o n g . 7O 3 0 . 3 * ~ , . at. 6O 5 5 . 3 * ~

AZIMUTH OF AB: 30°

REDUCLD THICKNESS

( m )

1.52

1.46

2.25

101.7

1.29

3.56

3.53

3.20

5.23

3.81

2.91

4.62

5m17

10.53

3 091

REDUCE. DEPTH

(m)

DATE : -

REDUCED I A B / ~ ] CALC. VES

( ohm-m )

948.80

950.09

952.12

955 018

960.66

972.88

1002.64

1175.58

1690o90

2062m80

2431.05

3319.25

4177015

5025 l 24

6724.14

843 2 a10

10139.21

13719.18

17643057

25556.46

30108.93 33070.26

TABLE 4-3b DIRECT INTERPRETATICN RESULT

AZIMUTH OF AS: 120°

REDUCED THICKNESS

( m )

R E D U C E D D E P T H

( m >

R E D U C E D R E S I S T I V I T Y

( Ohm-m )

0 - CALC. V E S

( o h m - m )

1026m94

1027,74

102gm45

103 l m 9 6

1035,26

1O4Om88

1053,21

1133.33

1476m30

l773,62

2085.38

2859,92

3603,91

4321 e87

5709,32

' 7060.33

8390m55

11008.55

14212,34

20391,54

23954,OS

252176.90

O B S E R V E D VE S

( 0hm-m 1 I

1049,83

IO51.2O

1052.69

' 1053,O

l o s f 1047,06

1036m16

1069,96

1463.30

178?am70

2106,09

2869,03

3591e58

4291 m63

5648m45

6962-45

8249.33

10788,95

13950.14

20227.20

28930m44

26365.84

TABLE 4.4a DIRECT INTERPRETATION RESULT

LOCATION : I heakpu

COORDINATES : Long 7O 2 9 . 7 1 ~ , at. 6O 54 .61~

AZIMUTH OF AB: 75O DATE: 1/5/90

f-

REDUCED THICKNESS

( m )

0 .95

0.53

1.21

2.28

1-

7 REDUCED DEPTH (m)

0.95

1 .48

2.69

REDUCED RESISTIVITY

- -1

I CALC. VES OBSERVED

VE S ( ohm-m ) ( o h m - m )

I C

0.15 634.63

TABLE 4.4b D I R E C T IIiTSFIFRET.hTIGN RESULT

LOCATION: ~ h e a k p u

0 COORDINATES: Long. 7 2 9 . 7 1 ~ , at. 6O 5 4 . 6 1 ~

0 AZIMUTH OF AB: 165 - DATE: 1 /5 /90

REDUCED T H I C K N E S S

( m )

REDUCED DEPTH

( m )

1.39

2-88

8.25

6.58

7.93

11 -86

16.31

20.79

28.80

34.09

38e07

45 e66

54e70

76.36

79.57

REDUCED R E S I S T I V I T Y

( ohm-m

TrtBLE 4.5a DIRECT INTER1 RETATION RESULT

LOCATION : R he aka ( ~ i k k e ) 0

COGRDI NATES : Long. 7 29 .01~ , at. 6 O 5 3 . 8 1 ~

AZIMUTH OF AB: 2Z0 DATE: 2/5/90, -

REDUCED THICKNESS

( m )

REDUCED DE FTH

( m )

1.85

2.87

4.78

6 . lo 7.63

11 -80

15-75

18-93

21.58

24.67

26.94

31.26

37.20

49.38

55.06


( ohm-m

0

:ALCw VES

( ohm-m )

608.35

610.10

613.31

621.24

641 040

690.38

795 099

1215087

1492.80

1754.22

2361.71

2945 -68

3533.08

4738.12

5969084

7208.72

9670.52

12690.44

18534.88

21930.62

24152.95

OBSERVED VES

( ohm-m )

TABLE 4*5b DIRECT INTERPRETATION RESULT

LOCATION : hea aka ( ~ i k k e )

0 COORDINATES: Long. 7 26.0,~, at. 6O 53.81~

AZIMUTH OF AB: 115O

REDUCED THICKNESS

REDUCED DEPTH

( m )

1e93

2,91

4e54

5,60

7.21

lle81

16e55

2Oe9O

26 e 4 8

29e16

29.56

31e66

38.96

59e99

63e34

DATE: 2/5/90 -

REDUCED AB/ 2 R E S I S T I V I T Y

( ohm--m ) ( m >

Oe30

0

L C a V E S OBSERVED VE S

: ohm-m ) ( ohm-m ) -

1

L


LOCATION: u m u s i g i d e

AZIMUTH OF AB: 16O

REDUCED THICKNES

REDUCED DEPTH (m)

oa97

1.47

2.62

5.32

7,17

l l a 2 8

42.54

51e11

53a35

56.64

60a13

63,04

99997296 ,O

DATE: 5/5/90 -


( ohm-m 1

- CALC. VES

( ohm-m 1

2417a44

2421 a42

2427.71

2443,68

2485a32

2591,57

2838.37

3864a23

5488,96

6213,72

6766,73

7708,80

8301.24

8727a36

9443 -68

10255054

11267.01

13820a30

17588.64

25661 -03

30511,45

337l3,59

-----

OBSERVED VES

( oh-m 1

TABLE 4.6b DIRECT INTERPRETATION RESULT

LOCAT1 ON : Urnusigide

COORDINATES: Long. 7O 3 3 . 5 ~ ~ , L a t e 6O 5 3 . 7 ~ ~

AZIMUTH OF AB: 106O DATE: 5/5/90 - - - - -

REDUCED THICKNESS

(m > REDUCED DEPTH

(m)

0.97

1.47

2.69

5.26

7.64

13.86

18 ..96

23.96

31 l 24

33e19

36.19

39.15

45,23

69.03

9999754.0

REDUCED RESISTIVITY

( Ohm-m )

OBSERVED VE S

( Ohm-rn )

2508 m94

2513.23

2520.73

2536.60

2375.59

2685.08

2952.26

4002,08

5602.47

6285.92


LCCATI ON : ohulor

COORDINATES: L o n g .

AZIMUTH OF AB: lo0 DATE: 5/5/90 -


( ohm-m

0

:ALC. VES

( ohm-m )

BSERVED

1603.15

1603 -58

1604.27

1603.72

1626.03

1663.67

1749.58

2105.22

2587.03

2837.71

3106 25

3882.62

4738.28

5611.07

7320.88

8958.04

10541.80

13647.80

17541.89

25448.56

30203 .O5

33356094

TABLE 4 .7b DIRECT INTERPRETATION RESULT

LOCATION : o h u l o r

0 COORDINATES : Long . 7 30 .91~, ' at. 6 O 54 .51~

DATE : -

REDUCED THICKNESS

( m )

REDUCED DEPTH (m)

EDUCED E S I S T I V I T l ( ohm-m

- :ALCo VES

( ohm-m )

IBSERVEP, VES

( ohm-m )

b

APPENDIX 4 - FIGURES 6.1 - 6.7 - COMPUTED - RESISTIVITY PROFILES, LOWER AND UPPER AZIMUTHS OF EACH

STATION COMPARED

A P P E N D I X 4. - F I G U R E S 6 . 1 - 6 . 7 :

COMPUTED R E S I S T I V I T Y PROFILES, L O W E R A N D

UPPER A Z I M U T H S C O M P A R E D .

1 b

10 x 5 CI

4- i c 0 - 3- 0 a\ -

2- k > - C V)

rot 9- 40° azimuth

a 8-

4- 7- z 6- ," .. W a 5- a a 4- P

a 3- 130° azimuth

I o~~ 2 I I I I 1 1 1 1 1 , I I 1% I

1 1 L

2 3 4 5 6 7 8 9 1 0 i i 4 5 i h 'C io2 115 2 x 1 0 ~ E L E C T R O D E S P A C I N G , A B 1 2 ( m )

FIG. 6 .1 : COMPUTED RESISTIVITY PROFILES, LOWER AND

UPPER A Z I M U T H S COMPARED , UMUEZEJOR 1

UGBAIKE BOUNDARY, L o n g . 7 O 30.9 '€ , Lot. 6O55.5~

40'1 130" a z i m u t h s 2314 190

I 2 3 4 5 6 7 8 9 1 0 2 3 4 5 6 7 8 9 ~ ~ 1-5 2x10~ E L E C T R O D E S P A C I N G , A B / 2 ( m )

- - - - ----- F I G . 6 . 2 : COMPUTED R E S I S T I V I T Y PROFILES, LOWER AND - - - - UPPER AZIMUTHS COMPARED; U G B A I K E ,

Long. 7 0 3 0 - 8 ' ~ , L o t . 6 ' 5 5 . 9 ' ~ ; 30" -AND 125' a z i m u t h s , 2 4 / 4 1 9 0 .

I o'x 7 ,

I 2 3 4 5 6 7 8 9 1 0 2 3 4 5 6 7 8 9 1 0 - 1-5 2x10 E L E C T R O D E S P A C I N G , A B / 2 ( m )

FIG.6 3 : COMPUTED RESISTIVITY PROFILES, LOWER AND UPPER ( 3 0 ° AND 120° ) AZI MUTHSCOMPARED ;

UMUEZE J,OR, Long. 7O30 - 3 E'; La t . 6 0 5 5 - 3 ' ~ ,

1/5 /90

E L E C T R O D E S P A C I N G , A B / 2 ( o h m - m )

FIG. 6 . 4 : COMPUTED- RESISTIVITY PROFILES, LOWER AND UPPER (75"-AND 165") AZIMUTHS COMPARED IHEAKA; Long. 7" 2 9 . 7 ' E , Lat. 6" 5 4 + 6 ' ~ , 1 / 5 / 9 0

E L E C T R O D E S P A C I N G , A 0 1 2 ( m )

F I G . 6 . 5 : COMPUTED-RESIST IVITY PROFILES, LOWER AND

UPPER ( 2 2 " - A N D 115") AZIMUTHS COMPARED; IHEAKA (LIKKE 1 , Long. 7 ° 2 9 - 0 ' E , Lat . 6 0 5 3 . 8 ' ~ , 2/ 5 / 9 0

E L E C T R O D E SPACING, AB/2 ( m )

FIG. 6 .6 : COMPUTED RESISTIVITY PROF1 LES, LOWER AND

UPPER ( 1 6 ° - A N 0 0 6 0 ) AZIMUTHS COMPARED; UMUSIGIDE , L o n ~ . 7 ~ 3 3 . 5 ' € , ~ a t . 6 O 53 . 7 ' N , 5 / 5 1 90


F I G . 6 . 7 : COMPUTED R E S I S T I V I T Y P R O F I L E S , LOWER AND U P P E R (10"-AND1OOO ) A Z I M U T H S C O M P A R E D ,

O H U L O R , Long . 7 " 3 0 . 9 ' ~ ~ L a t . 6 " 54.5 N ,

5 / 5 / 9 0

-

GULLY S I T E BY KM 27 TO IKEM ALONG OBOLLO AFDR - ADDA ROAD.

PLATE 1:

PLATE 2: FRACTURE S E T T I N G I N A HOUSE AT UPIUEZE JOR.

APPENDIX 9 - TABLES 5 1-5.7:

C O E F F I C I E N T S O F APPARENT ANISOTROPY PER GEOSOUNDING STATION.

TABLE 5.1 COEFFICIENTS OF APPARENT ANISOTROPY FOR

UMUEZEJOR/UGBAIKE BOUNDARY

APPARENT RESISTIVITY, fa (Ohm-m)

0 40 azimuth 0 130 azimuth

COEFFICIENT OF APPARENT ANISOTROPY ( ha)

TABLE 5.2 COEFFICIENTS OF APPARENT ANISOTROPY FOR UGBAIKE

APPARENT RESI

125O azimuth 1 ---------------- 1472.72

COEFFICIENT OF APPARENT ANISOTROPY ( m ---------------

1.07

1.10

1.0

1.09

1.09

1.0 * 1.14

1.83

1.96

1.94

TABLE 5.3

I? 2

COEFFICIENTS OF APPARENT ANISOTROPY FOR UMUEZEJOR

APPARENT RESISTIVITYt & (Ohm-m)

0 30 azimuth 120° azimuth

COEFFICIENT OF APPARENT ANISOTROPY

( m

TABLE 5.4

12 3

COEFFICIENTS OF APPARENT ANISOTROPY FOR IHEAKPU

APPARENT RESISTIVITY, [ohm-m)

0 165 azimuth ---------------- 1165.02

1265.16

1583.68

2786.46

4203.14

8989.06

13855.46

17985.73

COEFFICIENT OF APPARENT ANISOTROPY

( m

TABLE 5.5 COEFFICIENTS OF APPARENT ANISOTROPY FOR IHEAKA

APPARENT RESI G

22' azimuth -------------- 621.24

795.99

1492.80

2361.71

4738.12

5969.84

9670.52

12690.44 --------------

;TIVITY ' Ohm-ml

115' azimuth ---------------- 739.79

924.96

1716.39

2603.95

4658.95

5738.45

9118.68

11936.84

TABLE 5.6

12 5

COEFFICIENTS OF APPARENT ANISOTROPY FOR UMUSIGIDE

APPARENT RESISTIVITY, Sa ohm-m 1

COEFFICIENT OF APPARENT ANISOTROPY ( aa) ---------------

1.04

TABLE 5.7

12 6

COEFFICIENTS OF APPARENT ANISOTROPY FOR OHULOR

APPARENT RESISTIVITYt

0 LOO azimuth

1608.45

1801.33

2194.22

3128.84

5273.04

7893.40

10827.31

12915.56

17074.93 -----------------

COEFFICIENT OF APPARENT ANISOTROPY ( M --------------- 1.02

university of nigeria · university of nigeria research publications author udom, iboro demas pg/m....

Documents