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
[email protected], GFZ-Potsdam
ENS Paris
ENS Paris
UC Santa Cruz
EGU2020!
what’s in it for me?
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