Crustal Deformation from the 2004 Sumatra-Andaman Earthquake ...
Crustal Deformation from the 2004 Sumatra-Andaman Earthquake ...
Crustal Deformation from the 2004 Sumatra-Andaman Earthquake ...
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<strong>Crustal</strong> <strong>Deformation</strong> <strong>from</strong> <strong>the</strong> <strong>2004</strong><br />
<strong>Sumatra</strong>-<strong>Andaman</strong> <strong>Earthquake</strong> detected<br />
by Continuous GPS in Sou<strong>the</strong>ast Asia<br />
From <strong>the</strong> website of NOAA<br />
Manabu Hashimoto (DPRI, Kyoto Univ.)<br />
Michio Hashizume(Chulalongkorn Univ.) ,<br />
Nithiwatthn CHOOSAKUL, Hiroshi Takiguchi, Shuzo Takemoto,<br />
Yoichi Fukuda, Kunio Fujimori (KUGI, Kyoto Univ.)<br />
Mikio Satomura (Shizuoka Univ.),Wu Peiming (JAMSTEC),Yuichi<br />
Otsuka (STE Lab., Nagoya Univ.),Takashi Maruyama, Susumu<br />
Saito (NICT),Teruyuki Kato (ERI, Tokyo Univ.)<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
1
The <strong>Sumatra</strong>-<strong>Andaman</strong> and Nias<br />
<strong>Earthquake</strong>s<br />
• Great interplate earthquakes<br />
– Dec. 26, <strong>2004</strong> <strong>Sumatra</strong>-<strong>Andaman</strong> eq.(Mw9.3)<br />
– Mar. 28, 2005 Nias eq.(Mw8.6)<br />
• Basic questions<br />
– Why such a large event occurred<br />
– Is slip slow or fast beneath <strong>Andaman</strong><br />
• GPS observation will give answers to <strong>the</strong>se<br />
questions.<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
2
Slip Distribution Derived From <strong>the</strong><br />
Inversion of Seismic Waveforms<br />
• Maximum slip off <strong>Sumatra</strong><br />
• Large slip near Nicobar Islands<br />
• No significant slip beneath <strong>Andaman</strong> Islands<br />
Ammon et al. (2005)<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
3
Horizontal<br />
Displacements in<br />
Nor<strong>the</strong>rn <strong>Sumatra</strong><br />
and <strong>Andaman</strong> –<br />
Nicobar Islands<br />
Subarya et al.(2006)<br />
• 3~6m SWS-ward<br />
displacements<br />
• Uplift or subsidence<br />
up to 3m<br />
• Can not be explained<br />
by seismic model<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
4
Slip Distribution<br />
Derived <strong>from</strong> <strong>Crustal</strong><br />
<strong>Deformation</strong><br />
(Subarya<br />
et al.,2006)<br />
• Three asperities<br />
• These asperities were<br />
linked to be a M9 event.<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
5
Coseismic Displacements of Continuous GPS Sites:<br />
Differences Between Averaged Positions 5 days before & that of Dec.27<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
6
Coseismic Displacements<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
7
Summary of Coseismic Displacements<br />
<strong>from</strong> <strong>the</strong> <strong>Sumatra</strong>-<strong>Andaman</strong> EQ<br />
• Global effects<br />
– 26cm at Phuket<br />
– Several mm in Philippine<br />
– ~10mm in India<br />
• Slip distribution<br />
– Large slips off <strong>Sumatra</strong> and beneath Nicobar<br />
– Small but significant slip beneath <strong>Andaman</strong><br />
• Estimated geodetic moment = 9.1~9.2<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
8
Postseismic Movements Following <strong>the</strong><br />
<strong>Sumatra</strong>-<strong>Andaman</strong> and Nias <strong>Earthquake</strong>s<br />
• Postseismic movements<br />
– ~20yrs. for Nankai eq.; ~40yrs. for Alaska eq.<br />
– How long for <strong>Sumatra</strong> eq.<br />
– Existence of <strong>Andaman</strong> Sea = opening back-arc<br />
• Objective: To reveal crustal movement <strong>from</strong><br />
GPS data and study <strong>the</strong>ir mechanism<br />
– Spatial and temporal variations<br />
– Modelling of postseismic movements<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
9
Mechanism of Postseismic Movement<br />
• Viscoelastic relaxation<br />
– Relaxation of stresses caused by faulting due to viscous<br />
flow in lower crust and mantle<br />
• Afterslip<br />
– Slip on source fault or its extension<br />
– 3 different models in this category<br />
• Poroelastic rebound<br />
– Flow of porous water due to pressure changes caused<br />
by faulting<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
10
Site Distribution<br />
• 11 sites in Thailand<br />
• 3 sites in Indonesia<br />
• 1 site in Singapore and<br />
Myanmar each<br />
• Complex tectonics<br />
– Oblique subduction of<br />
Indo-Australia plate<br />
– Back-arc opening in<br />
<strong>Andaman</strong> Sea<br />
– <strong>Sumatra</strong> and Saging<br />
Oct. 14, 2006<br />
faults<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
11
Phimai Observatory<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
12
Nong Khai<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
13
Chiang Mai<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
14
Analysis of GPS data (1)<br />
• Data<br />
– 21 IGS sites<br />
– 1 Bakosrutanal site (SAMP)<br />
– 1 STEL site (PDNG)<br />
– 4 KU-CU sites (PHMI, NNKI, UBRT, SIS2)<br />
– 3 CU-JAMSTEC sites (PHKT, BNKK, CHMI)<br />
– 1 SU site (KKUT)<br />
– 1 SU-JAMSTEC site (YNGN)<br />
– 3 NICT sites (CPN,KMI, CMU)<br />
• Dec. 5, <strong>2004</strong> ~ Dec. 31, 2005<br />
• 30 sec. sampling<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
15
Analysis of GPS Data (2)<br />
• Static analysis<br />
– Bernese 5.0/ BPE<br />
– IGS Final ephemeredes, earth rotation parameters and clock<br />
offsets<br />
– Estimate of tropospheric delay at every two hours<br />
– Estimate of horizontal gradient of tropospheric delay<br />
– GOT00.02 for ocean loading model<br />
– Constrain to distant sites to ITRF2000 (USUD, BAHR etc)<br />
– Application of spatial filter<br />
– Transform of displacements to those referring to <strong>the</strong> Sunda<br />
block using <strong>the</strong> model of Bock et al.(2003)<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
16
Time Series of<br />
Coordinate<br />
Changes at<br />
Phuket and<br />
Sampari<br />
Phuket:<br />
Coseismic ~26cm<br />
and<br />
Postseismic<br />
~19cm during 1 yr<br />
ITRF2000<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
17
Time Series of Coordinate Changes at Sites<br />
in SE Asia<br />
Bangkok: coseismic ~7cm, postseismic ~6cm<br />
ITRF2000<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
18
Horizontal Displacements during and after<br />
<strong>the</strong> <strong>Sumatra</strong>-<strong>Andaman</strong> EQ<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
19
Fitting to time series of<br />
postseismic movements<br />
• Montesi’s(<strong>2004</strong>) model for plastic flow<br />
D<br />
s<br />
o<br />
{ 1 [ 1 (1 1/ ) ]<br />
1/(1 )<br />
}<br />
−n<br />
− + − n t<br />
= D + nV<br />
τ<br />
0<br />
τ<br />
/<br />
• Period of fitting<br />
– Whole period (PHKT,CPN,BNKK,SIS2,CHMI)<br />
– After <strong>the</strong> Nias eq.(SAMP)<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
20
Fitting of<br />
Analytic<br />
Function<br />
Logarithmic /<br />
power-law<br />
functions are<br />
better<br />
→Controlled<br />
by friction<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
21
Fitting to <strong>the</strong> Time Series of<br />
SAMP after <strong>the</strong> Nias EQ<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
22
Parameters for fitting to<br />
postseismic movements<br />
Site 1/n τ(days) V 0<br />
(mm/day) Do(mm)<br />
PHKT -0.60 0.5 18.3<br />
4.8<br />
CPN 0.20 65.0 1.0 16.2<br />
BNKK -0.70 0.5 4.6 2.3<br />
SIS2 -1.00 0.5 1.6 3.5<br />
CHMI -0.15 200.0 0.1 3.5<br />
SAMP* -0.15 1.0 17.6 -9.3<br />
Oct. 14, 2006<br />
Negative exponent<br />
Short time constant<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
23
Variable Slip Models for Postseismic Displacements<br />
Maximum 2m slip<br />
Bfr Nias EQ: Peak off <strong>the</strong> NW <strong>Sumatra</strong><br />
Slip beneath <strong>the</strong> central <strong>Andaman</strong><br />
Aft Nias EQ: Peak near Nicobar<br />
Decrease of slip beneath <strong>Andaman</strong><br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
24
<strong>Sumatra</strong> – <strong>Andaman</strong> EQ: Summary of<br />
Observation of Postseismic Displacements<br />
– Time series can be fit by logarithmic or power-law functions<br />
• Controlled by friction on <strong>the</strong> fault<br />
– Before Nias earthquake<br />
• Largest at Phuket; small at Sampari<br />
• Largest slip NW off <strong>Sumatra</strong><br />
• No significant slip beneath nor<strong>the</strong>n <strong>Andaman</strong><br />
– After Nias earthquake<br />
• Large effect <strong>from</strong> Nias EQ at Sampari and Singapore<br />
• Postseismic displacements following <strong>the</strong> S-A EQ in Thailand<br />
• Small displacement at Yangong<br />
• Largest slip beneath Nicobar Islands<br />
• Reduction of slip area beneath <strong>Andaman</strong> Islands<br />
Oct. 14, 2006<br />
GPS Symposium in Chulalongkorn<br />
Univ., Bangkok<br />
25