Preliminary Results of Rupture Process for 2004 OFF COAST OF NORTHERN SUMATRA Giant Earthqauke (ver. 1)


Old version (ver. 0)

On December 26, 2004 (GMT), a thrust-faulting giant earthquake (Mw 9.0) struck off coast of northern Sumatra. To estimate rupture process of this giant earthquake, I retrieved teleseismic body waves (P-waves) data recorded at IRIS-dmc stations via Internet. 13 stations were selected from the viewpoint of good coverage, and used in the waveform inversion with ABIC (Fukahata et al., 2003; Yagi et al., 2003).
From a broadband seismic wave, we can divide the giant earthquake into two stages. In first stage, the rupture mainly propagated to the northwest from hypocenter during initial 100 sec. The second rupture started about 100 sec after initial break. The second rupture generate ultra long period seismic wave. This may imply that slow and large dislocation occurred in the second stage. Form a high frequency component of seismic wave, I rough estimated the duration of source process, and found that the duration may exceed 400 sec (figure: duration of shaking = source duration + sP-Ptime). Unfortunately, the period of seismic wave of the second stage is too long to analyze my program set. In this web-site, I estimated a part of rupture process using waveform that were bandpassed between 4 and 200 sec.

Yuji Yaig (IISEE, BRI, 2004)


Map View


Figure: Hypocenter determined by USGS. Blue lines represent the extent of the fault plane used in our inversion.

Distribution of fault-slip and Moment-rate function


Figure : (upper left) Focal mechanism; (upper right) Total moment-rate function; (lower) Distribution of coseismic slip. Star indicates the location of the initial break. The average rupture propagation velocity is about 2.5 km/sec.

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; 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, Y. ; 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), Bull. Seism. Soc. Am., 94, 1795-1807, 2004.


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Last Updated: 2005 Jan. 12