Simeuleu island

The The AcehAceh/Andaman earthquake:/Andaman earthquake:

WhatWhat’’s next?s next?

Kerry Sieh

Tectonic Observatory, Caltech

11 March 2005

Indo-burmansource(s)

westSumatransources

Indian Ocean Sumatra

WEST EAST

Courtesy ofRobinLacassin,IPG Paris

What do we know about the2004 rupture?

WEST EAST

The pattern and magnitude of submergence anduplift constrain the rupture location and amount

Photo by Denis Giles

Camorta island, Nicobars

QuickBird 23 June 2004 QuickBird 28 December 2004

Banda Aceh

before after

Great Nicobar island

before after

Courtesy of Aron Meltzner,Tectonics Observatory,

Caltech

North Sentinel island, Andaman island group

before after

Courtesy of AronMeltzner, TO, Caltech

Just off the WWW,from Centre forEarth ScienceStudies, Trivandrum,India

http://www.seires.net/content/view/122/52/

GPS horizontaldisplacements

Simeuleuisland

Courtesy of Robin Lacassin,IPG Paris

2004

Helicopter crew

Boat crew

Science team Logistics and GPSDayat

Samsir

Man et al

Me

Danny Natawidjaja

John Galetzka

Imam Suprihanto

Bambang Suwargadi

MohamedChlieh

100 km

Simeulue island, Aceh, Sumatra

Annual lowest tide(“highest level ofsurvival” or “HLS”)

Substrate

Coral head

The coral “instrument”

130 cm

130 cm

155 cm

Submergence before the uplift

There must be an interesting story in here!!

From Danny Natawidjaja’s Ph.D. thesis,Tectonic Observatory, Caltech, 2003

Oops!

8 meters

15˚ dip

Trench to 43 kmdepth

First attempt to model theuplift, Mohamed Chlieh,Tectonics Observatory,Caltech

8 meters

15˚ dip

Trench to 43 kmdepth

2 segments

8 meters

15˚ dip

Trench to 43 kmdepth

2 segments

98 cm, 2004

5 cm, 2002

100 km

100 km

2004

19071861

1935

1797/1833

Submergence rates of thepast 50 years …

-1

… suggestthat the depthof locking ofthesubductioninterfacevaries alongstrike

-1

From MohamedChlieh, TO, Caltech

The wider thepatch, thebigger thepotentialearthquake?

To improve our measurements of deformation,we began installing the Sumatran GPS Array(SuGAr) in 2002

48

43

31

29

34 32

Mapping the great 2002 ruptureinspired many questions

Modeling of campaignand continuous GPSvelocity vectors alsosuggests that the depthof locking varies widelyalong strike

Mapping the great 2002 ruptureinspired many questions

Let’s take a look at thelonger term.

First here

Then here

Paleogeodetic records near the Equator show very-long-termchanges in vertical rates of deformation

~1380

~1605

17971833

To the south, we see repeating giantearthquakes

1833

18161808 1797

Two giant earthquakes and intermittent interseismic submergence

1797

90 cm

1797

Uniform 4 m slip Mw 8.2

1833

200 cm

1833

Uniform 10 m slip Mw 8.7

1833

Uniform 10 m slip Mw 8.7

1833

1797

1935

?

?

Smallerearthquakes,thinner lockedpatches.

Giantearthquake,thicker lockedpatches.

1797, M > 8.4

Recall that at some sites, upliftepisodes appear to be roughlyperiodic

An Indo-burmansource(s)

westSumatransources

Singapore

Jakarta

Kuala Lumpur

The past record of large megathrust events inNorth and West Sumatra suggests the nextevents are not too far off

Singapore

Jakarta

Kuala Lumpur

1797

Most of the megathrust failedbetween 1797 and 1907

Singapore

Jakarta

Kuala Lumpur

18331797

Most of the megathrust failedbetween 1797 and 1907

Singapore

Jakarta

Kuala Lumpur

18331797

1861

Most of the megathrust failedbetween 1797 and 1907

Singapore

Jakarta

Kuala Lumpur

18331797

18611907

Most of the megathrust failedbetween 1797 and 1907

Singapore

Jakarta

Kuala Lumpur

18331797

18611907

1935

A 70-km long patch failed in 1935,between the giant 1861 and 1833patches

Singapore

Jakarta

Kuala Lumpur

18331797

18611907

1935

A flurry of ruptures have occurredsince 2000

2000

2002

2004

Singapore

Jakarta

Kuala LumpurNext?

19071935

2000

2002

2004

Based upon what we have seen in the coral microatolls, I expect that we will seetransients in the months, years or decades between the 2004 Aceh/Andamanearthquake and the next west-Sumatran earthquakes. … the TO will be ready!

Thankyou

(My survivor buddiesaround a tsunami

block, Simeulueisland)

Coseismichorizontalvectors fromSuGAr (in mm).

Model

Data