Crustal Deformation from the 2004 Sumatra-Andaman Earthquake ...

Crustal Deformation from the 2004 

Sumatra-Andaman Earthquake detected 

by Continuous GPS in Southeast Asia 

From the website of NOAA 

Manabu Hashimoto (DPRI, Kyoto Univ.) 

Michio Hashizume(Chulalongkorn Univ.) , 

Nithiwatthn CHOOSAKUL, Hiroshi Takiguchi, Shuzo Takemoto, 

Yoichi Fukuda, Kunio Fujimori (KUGI, Kyoto Univ.) 

Mikio Satomura (Shizuoka Univ.),Wu Peiming (JAMSTEC),Yuichi 

Otsuka (STE Lab., Nagoya Univ.),Takashi Maruyama, Susumu 

Saito (NICT),Teruyuki Kato (ERI, Tokyo Univ.) 

Oct. 14, 2006 

GPS Symposium in Chulalongkorn 

Univ., Bangkok 

1

The Sumatra-Andaman and Nias 

Earthquakes 

• Great interplate earthquakes 

– Dec. 26, 2004 Sumatra-Andaman eq.(Mw9.3) 

– Mar. 28, 2005 Nias eq.(Mw8.6) 

• Basic questions 

– Why such a large event occurred 

– Is slip slow or fast beneath Andaman 

• GPS observation will give answers to these 

questions. 

Oct. 14, 2006 



2

Slip Distribution Derived From the 

Inversion of Seismic Waveforms 

• Maximum slip off Sumatra 

• Large slip near Nicobar Islands 

• No significant slip beneath Andaman Islands 

Ammon et al. (2005) 

Oct. 14, 2006 



3

Horizontal 

Displacements in 

Northern Sumatra 

and Andaman – 

Nicobar Islands 

Subarya et al.(2006) 

• 3~6m SWS-ward 

displacements 

• Uplift or subsidence 

up to 3m 

• Can not be explained 

by seismic model 

Oct. 14, 2006 



4

Slip Distribution 

Derived from Crustal 

Deformation 

(Subarya 

et al.,2006) 

• Three asperities 

• These asperities were 

linked to be a M9 event. 

Oct. 14, 2006 



5

Coseismic Displacements of Continuous GPS Sites: 

Differences Between Averaged Positions 5 days before & that of Dec.27 

Oct. 14, 2006 



6

Coseismic Displacements 

Oct. 14, 2006 



7

Summary of Coseismic Displacements 

from the Sumatra-Andaman EQ 

• Global effects 

– 26cm at Phuket 

– Several mm in Philippine 

– ~10mm in India 

• Slip distribution 

– Large slips off Sumatra and beneath Nicobar 

– Small but significant slip beneath Andaman 

• Estimated geodetic moment = 9.1~9.2 

Oct. 14, 2006 



8

Postseismic Movements Following the 

Sumatra-Andaman and Nias Earthquakes 

• Postseismic movements 

– ~20yrs. for Nankai eq.; ~40yrs. for Alaska eq. 

– How long for Sumatra eq. 

– Existence of Andaman Sea = opening back-arc 

• Objective: To reveal crustal movement from 

GPS data and study their mechanism 

– Spatial and temporal variations 

– Modelling of postseismic movements 

Oct. 14, 2006 



9

Mechanism of Postseismic Movement 

• Viscoelastic relaxation 

– Relaxation of stresses caused by faulting due to viscous 

flow in lower crust and mantle 

• Afterslip 

– Slip on source fault or its extension 

– 3 different models in this category 

• Poroelastic rebound 

– Flow of porous water due to pressure changes caused 

by faulting 

Oct. 14, 2006 



10

Site Distribution 

• 11 sites in Thailand 

• 3 sites in Indonesia 

• 1 site in Singapore and 

Myanmar each 

• Complex tectonics 

– Oblique subduction of 

Indo-Australia plate 

– Back-arc opening in 

Andaman Sea 

– Sumatra and Saging 

Oct. 14, 2006 

faults 



11

Phimai Observatory 

Oct. 14, 2006 



12

Nong Khai 

Oct. 14, 2006 



13

Chiang Mai 

Oct. 14, 2006 



14

Analysis of GPS data (1) 

• Data 

– 21 IGS sites 

– 1 Bakosrutanal site (SAMP) 

– 1 STEL site (PDNG) 

– 4 KU-CU sites (PHMI, NNKI, UBRT, SIS2) 

– 3 CU-JAMSTEC sites (PHKT, BNKK, CHMI) 

– 1 SU site (KKUT) 

– 1 SU-JAMSTEC site (YNGN) 

– 3 NICT sites (CPN,KMI, CMU) 

• Dec. 5, 2004 ~ Dec. 31, 2005 

• 30 sec. sampling 

Oct. 14, 2006 



15

Analysis of GPS Data (2) 

• Static analysis 

– Bernese 5.0/ BPE 

– IGS Final ephemeredes, earth rotation parameters and clock 

offsets 

– Estimate of tropospheric delay at every two hours 

– Estimate of horizontal gradient of tropospheric delay 

– GOT00.02 for ocean loading model 

– Constrain to distant sites to ITRF2000 (USUD, BAHR etc) 

– Application of spatial filter 

– Transform of displacements to those referring to the Sunda 

block using the model of Bock et al.(2003) 

Oct. 14, 2006 



16

Time Series of 

Coordinate 

Changes at 

Phuket and 

Sampari 

Phuket: 

Coseismic ~26cm 

and 

Postseismic 

~19cm during 1 yr 

ITRF2000 

Oct. 14, 2006 



17

Time Series of Coordinate Changes at Sites 

in SE Asia 

Bangkok: coseismic ~7cm, postseismic ~6cm 

ITRF2000 

Oct. 14, 2006 



18

Horizontal Displacements during and after 

the Sumatra-Andaman EQ 

Oct. 14, 2006 



19

Fitting to time series of 

postseismic movements 

• Montesi’s(2004) model for plastic flow 

D 

s 

o 

{ 1 [ 1 (1 1/ ) ] 

1/(1 ) 

} 

−n 

− + − n t 

= D + nV 

τ 

0 

τ 

/ 

• Period of fitting 

– Whole period (PHKT,CPN,BNKK,SIS2,CHMI) 

– After the Nias eq.(SAMP) 

Oct. 14, 2006 



20

Fitting of 

Analytic 

Function 

Logarithmic / 

power-law 

functions are 

better 

→Controlled 

by friction 

Oct. 14, 2006 



21

Fitting to the Time Series of 

SAMP after the Nias EQ 

Oct. 14, 2006 



22

Parameters for fitting to 

postseismic movements 

Site 1/n τ(days) V 0 

(mm/day) Do(mm) 

PHKT -0.60 0.5 18.3 

4.8 

CPN 0.20 65.0 1.0 16.2 

BNKK -0.70 0.5 4.6 2.3 

SIS2 -1.00 0.5 1.6 3.5 

CHMI -0.15 200.0 0.1 3.5 

SAMP* -0.15 1.0 17.6 -9.3 

Oct. 14, 2006 

Negative exponent 

Short time constant 



23

Variable Slip Models for Postseismic Displacements 

Maximum 2m slip 

Bfr Nias EQ: Peak off the NW Sumatra 

Slip beneath the central Andaman 

Aft Nias EQ: Peak near Nicobar 

Decrease of slip beneath Andaman 

Oct. 14, 2006 



24

Sumatra – Andaman EQ: Summary of 

Observation of Postseismic Displacements 

– Time series can be fit by logarithmic or power-law functions 

• Controlled by friction on the fault 

– Before Nias earthquake 

• Largest at Phuket; small at Sampari 

• Largest slip NW off Sumatra 

• No significant slip beneath northen Andaman 

– After Nias earthquake 

• Large effect from Nias EQ at Sampari and Singapore 

• Postseismic displacements following the S-A EQ in Thailand 

• Small displacement at Yangong 

• Largest slip beneath Nicobar Islands 

• Reduction of slip area beneath Andaman Islands 

Oct. 14, 2006 



25

Crustal Deformation from the 2004 Sumatra-Andaman Earthquake ...

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