Sumatra Earthquake

Preliminary Results of Rupture Process for The 2002 NORTHERN SUMATRA, INDONESIA EARTHQUAKE

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

I retrieved teleseismic body waves (P-waves) data recorded at IRIS-dmc stations via Internet. 19 stations were used in the waveform inversion. We assumed a reference fault model :(strike, dip, rake) = (298, 8, 72) which is inferred from the Harvard CMT solution. This focal mechanism is consistent with release of stress buildup on the inter-plate boundary in Subdction zone.

Result

The seismic moment Mo = 1.1e20 Nm (Mw 7.3);
The source duration T = 30 s;
Fault mechanism: (Strike, Dip, Slip)=(298, 8, 75) ;
Hypocenter: (lat.= 3.02N, lon.= 96.18E, depth= 16 km).
Rupture propagated upward and unilateral. Two asperities (large slip areas) are identified. The maximum dislocation is about 1.6 m. (Yagi, 2002)

Distribution of fault-slip

Fig. 1 : (upper left) Focal mechanism; (upper middle) Total moment-rate function; (lower) Distribution of coseismic slip. Star indicates the location of the initial break.

Snapshot of fault-slip

Fig. 2 : Snapshots of the interval dislocation.

Map View

Fig. 3: Hypocenter of the main-shock determined by USGS. Blue lines represent the extent of the fault plane used in our inversion.

Waveform comparison

Fig. 4 : 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- or S-wave arrival.

Fig. 5 : Telesesimic stations used in our inversion (Azimuthal Equidistant Projection). The star represents the epicenter of the main-shock.

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