INDONESIA Earthquake

Preliminary Results of Rupture Process for the March 28, 2005 NORTHERN SUMATRA, INDONESIA Earthquake

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

On March 28, 2005, great thrust-faulting earthquake (M = 8.7) occurred in Sumatra, Indonesia. This earthquake located on the interface between the India and Burma plates where India plate is subducting beneath the overriding Burma plate at a rate of about 4-6 cm/year. I retrieved teleseismic body waves (P-waves) data recorded at IRIS-dmc stations via Internet. 19 stations were selected from the viewpoint of good coverage, and used in the waveform inversion with ABIC (Fukahata et al., 2003, 2004; Yagi et al., 2003).

Result

The seismic moment Mo = 1.6 x 10**22 Nm (Mw 8.7);
The source duration T = 150 s;
(strike, dip, rake) = (329, 14, 115)
Hypocenter: (Lat. = 2.065N, Lon. = 97.010E, depth= 28 km).
[The epicenter of the main-shock was determined by USGS]

The rupture nucleated on south side of 2004 Sumatra Great Earthquake, and propagated 300 km to the southeast. The rupture propagated mainly along trench axis.The maximum dislocation is about 10 m.

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.