2005年3月28日スマトラ沖で発生した巨大地震 (M 8.7) について


Inversion was made using teleseismic data (provided by IRIS-DMC)

2004年12月26日に北スマトラ沖でM9の巨大地震が発生しました.ここでは、 IRIS-DMCが 収集している波形をABICを考慮した波形インバージョン法(Fukahata et al., 2003, 2004; Yagi et al., 2004) に適用して, 地震の時空間のすべり量分布の変化を求める事を求めました.

結果

地震モーメント Mo = 1.6 x 10**22 Nm (Mw 8.7);
破壊継続時間 T = 150 s;
(strike, dip, rake) = (329, 14, 115)
震源: (Lat. = 2.065N, Lon. = 97.010E, depth= 28 km).
[ここで,震央はUSGSの値を使用しました.]

破壊は,2004年スマトラ沖巨大地震(Mw9.5)の南側から始まり,南側に約300km伝搬しています.断層のずれは約10m(海底付近) にも及びますが,2004年スマトラ沖巨大地震(ずれの量40m程度)と比べると小さいです.今回の地震の破壊領域は,2004年の地震 の破壊領域と全く重なりません.従って,今回の地震は,2004年スマトラ沖巨大地震の余震と考えるより,別の地震と考える方が妥当です.

Note: Since I used the teleseismic body wave, the resolution of space is not so good. The maximum dislocation and fault area will be revised using the near-field data.
(Yagi, IISEE, 2003)

Distribution of fault-slip


Figure : (upper left) Focal mechanism; (upper right) Total moment-rate function; (lower) Distribution of coseismic slip. Star indicates the location of the initial break.

Map View


Figure: Hypocenter of the main-shock determined by USGS.

Waveform comparison


Figure : Comparison of the observed waveform (Black) with the calculated waveform (Red). The numbers below the station code indicate maximum amplitude in microns. The start time of the traces is lined-up at 10 (s) before the P-wave arrival.

Figure : Teleseismic stations used in inversion. The star represents the epicenter of the main-shock.

Reference

Fukahata, Y., Y. Yagi, and M. Matsu'ura, Waveform inversion for seismic source processes using ABIC with two sorts of prior constraints: Comparison between proper and improper formulations, GRL 30, 10.1029/2002GL016293, 2003.

Fukahata, Y.; A. Nishitani; M. Matsu'ura, Geodetic data inversion using ABIC to estimate slip history during one earthquake cycle with viscoelastic slip-response functions, Geophys. J. Int., 156, 140-153, 2004.

Yagi, Yagi ; T. Mikumo; J. Pacheco, Source rupture process of the Tecoman, Colima, Mexico earthquake of January 22, 2003, determined by joint inversion of teleseismic body wave and near-field data (PDF), submited to Bull. Seism. Soc. Am., 2003.

Links


If you have questions, please send to yagi@kenken.go.jp.

Last Updated: March 29, 2005