lockingdepth

shelf break coastline

Uplift

isostatic uplift

structural uplift

permanent interseismic uplift

Subsidence

low-stand

high-stand

transition

locked

total rock uplift

lockingdepth

shelf break coastline

Upliftisostatic uplift

permanent interseismic uplift

total rock uplift

structural upliftSubsidence

low-stand

high-stand

transition

locked

compressional-accretionary(e.g. Cascadia, Chile)

extensional-erosional(e.g. Central America, Ecuador-Colombia)

type of active margin

A B

distance from trench to shelf break and coastline, km

0

50

100

150

200

250

300

dist

ance

from

tren

ch to

lock

ing

dept

h, k

m

distance to locking, km

0

1

PD

F /

cum

ul. f

rac.

Shelf breakCoastline

50 100 150 200 250 350300 400 450-50 0

ratio

1:1

-50 0 50 100 150

Mw 9.2, Alaska (1964)

Mw 9.1, Tōhoku (2011)

Mw 8.3, Alaska Peninsula (1938)

Mw 8.6, Nias-Simeulue (2005)

Mw 7.9, September Sumatra EQs (2007)

Mw 8.4, SeptemberSumatra EQs (2007)

Mw 7.6, Nicaragua (1992)

Mw 7.4, Guatemala (2012)

Mw 7.3, El Salvador (2012)

Mw 8.3, Illapel (2015)

Mw 8.8, Maule (2010)

Mw 8.1, Iquique (2014)

Mw 8.6,Andreanof Isl. (1957)

Mw 8.1, Tōnankai (1944)

Mw 8.8, Ecuador-Colombia (1906)

Mw 7.6,Costa-Rica (2012)

Mw 7.2, Guerrero (2014)

shelf-width

coastlineshelf-break

0 50 100 150 200 250 300 350 400distance from trench to shelf break and coastline, km

0

50

100

150

200

250

300

dist

ance

from

tren

ch to

lock

ing

dept

h, k

m

Sumatra2,4

Nankai8

N. Honshu9,11

Hokkaido9

Aleutian15

Alaska15,16

Cascadia18,20

GTM-NIC24

Chile32,33,34

ratio

1:1

-50 50 100 150 200distance to locking, km

0

1

PD

F /

cum

ul. f

rac.

Shelf break Coastline

0

500 100 150 200 250 300 350 400 450distance trench to shelf break and to coast, km

0

50

100

150

200

250

300

dist

ance

from

tren

ch to

lock

ing

dept

h, k

m

NZ1

Sumatra2,3,4

Nankai5,6,7,8

N Honshu6,7,9,10,11

Hokkaido6,9,12

Kamchatka13

Aleutian14,15

Alaska15,16

Cascadia17,18,19,20

Mexico21,22

GTM-NIC23,24

Costa Rica23,24

COL-ECD25,26

Peru26,27 Chile27,28,29,30,31,

-200 -100 0 100 200 300distance to locking, km

0

1

PD

F /

cum

ul. f

rac.

Shelf break

Coastline

ratio

1:1

A: All subduction sites: B: Erosive sites with simple geometry and well-known coupling:

32,33,34,35

shelf-width

coastlineshelf-break

Tectonic geomorphology on the sea floor,

If I understand sedimentation and erosion,I may invert the topography for its active tectonic driver.

Sedimentation patterns and erosion processes are relatively well known

UTM 10T, Easting, 105 m

4.6

4.8

5

5.2

5.4

5.6

Nor

thin

g, 1

06 m

1 2 3 4 5 6

1

1.1

1.2

1.3

1.4

1.5

1.6

-1 0 1 2 3 4 5 6 7 8UTM 16P, Easting, 105 m

4

4.1

4.2

4.3

4.4

4 5 6 7 8UTM 54S, Easting, 105 m

200 km

100 km

McCaffrey et al. (2007)Burgette et al. (2009)Wang et al. (2003)Schmalzle et al. (2014)

Locking depth inversion

-4

-3

-2

-1

0

>1 kmElevation

-6

-4

-2

0

>1 km

200 km

100 km

200 km

100 km

A

C

B

-8

-4

-6

-2

0

>1 km

Lay et al. (2011)

Ye et al. (2013)

In 1996, Ruff & Tichelaar propose that coastlines sit above the downdip endof seismic coupling based on EQ outlines.Crustal buoyancy and subduction angle would explain it.

But the position of the coastline at active margins primarily depends onsea level and erosion. What gives?What are the morphological and active tectonic elements at a subduction?

Is the near universal downdip end of locking indeed reflected in morphology?

The locking depth appears to co-locate with the shelf break, not the coastlineLetʼs compile large megathrust EQs and see how they align or not withthe shelf break and the coastline at erosive continental shelves.

The shelf break is a much better predictor of the downdip end of large EQthan the coastline. Does the relationship hold by adding all information frominterseismic coupling studies?

Assuming that a small fraction of the interseismic deformation is not recov-ered during the coseismic rupture, it becomes an important driver of moun-tain building. And its location is linked to the location of the locking depth.

Uplift landward of the locking depth would feed rock into the domain of wave-base erosion. The shelf break would reflect a hingeline in long-term tectonic uplift (many earthquake cycles).How to link locking depth and uplift pattern I hear?

locking depthsfrom interseismicdeformation

Outlines of Mw ~7EQs in Central America

Outline of theTohoku-Oki EQ

This line is200 m depth

(~ shelf break)

Erosional truncation of deposits on the Cascadia Shelf. Wave erosion on the Santa Cruz coast, CA

What’s a subduction margin anyway?Geometries can vary widely according to subduction type,

The morphology of the seafloorrecords the combined action of

1) sedimentation,2) erosion, and

3) active tectonics

on geological timescales(>100 kyrs)

but one element is common: strain associated to seismic coupling.

Figure 5. East-west multichannel seismic reflection profile across the continental shelfat Stonewall Bank west of Alsea Bay (Fig. 1). The late Miocene unconformity (bold blackline) is angular landward of Stonewall Bank anticline, slightly angular just west of thebank where small wavelength folds are truncated, and conformable or disconformableseaward of these folds. This profile typifies the character of the unconformity from east

to west. Note that the unconformity truncates the late Miocene Columbia River Basaltflow (CRB) just east of well P-0093. Pliocene sediments onlap landward at a very low an-gle at the eastern end of the profile and are parallel to the unconformity elsewhere, indi-cating little relief on the unconformity at the time of erosion. After Yeats et al. (1998).

A feature along this linelies above the locking depth

Shelf breaks cluster above the locking

depth

Shelf breaks still cluster above the locking depth, using all compiled data all data (left) or

using a higher confidence selection (right)

Splay

fault

Splay

fault

BackthrustBackthrust

Underplating

CompressionCompression

Possibleextension regime

High basal shear strength

Thin trench fillStable taper angleStable taper angle

Extension

Subsidence SubsidenceSubsidenceSubsidenceSubsidence

UpliftUplift

Basal erosionBasal erosion

Frontal erosionFrontal erosion

Extensional nonaccretionary (erosional) typeCompressional accretionary type

spectrum of subduction margins

The position of the shelf is anchored by the onset of uplift above the locking depth. This robust observation can be explained by a local deformation signal driven by permannent interseismic deformation.

If the shelf break is linked to the locking depth, its morphologic sharpness could reflect the stability of the locking depth over 100ʼs kyr.

Underplating

Compression Compression

Possibleextension regime

SubsidenceSubsidenceSubsidence SubsidenceSubsidence

UpliftUplift

Basal erosionBasal erosion

Extensional nonaccretionary (erosional) type Compressional accretionary type

spectrum of subduction margins

locked thrust

narrow shelf wide shelf

The submarine morphology of an active margin reflects the state and distribution of coupling on the megathrust.

The shelf break is

located at the subsidence - uplift

hinge line, above the locking depth of

the subduction.

The position and shape of the shelf

break reflect coupling

patterns integrated

over 100ʼs kyr.

McNeill et al. (2000)

Nod

a (2

016)

Nod

a (2

016)

Co-location of the down-dip end of seismic lock-ing and the continental shelf break

Luca C. Malatesta

Lucile BruhatNoah J. Finnegan

Jean-Arthur L. OliveManuscript currently in revision

Preprint at https://eartharxiv.org/uwzbrFunded by the Swiss National Science Foundation

luca.malatesta@gfz-potsdam.de, GFZ-Potsdam

ENS Paris

ENS Paris

UC Santa Cruz

EGU2020!

what’s in it for me?

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