Preliminary Results of Rupture Process for May 21, 2003 NORTHERN ALGERIA Earthquake


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

On May 21, 2003, a destructive thrust-faulting earthquake (Mw = 6.7) occurred in Northern Algeria, where the plate boundary between the Eurasian plate and the African plate. I retrieved teleseismic body waves (P-waves) data recorded at IRIS-dmc stations via Internet. 14 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).

Result

The seismic moment Mo = 2.4 x 10**19 Nm (Mw 6.9);
The source duration T = 18 s;
(strike, dip, rake) = (54, 47, 86)
Hypocenter: (Lat = 36.89N , Long = 3.78E , depth= 10 km).
[The epicenter of the main-shock was determined by USGS]

The source process is characterized asymmetric bilateral rupture propagation. The main rupture mainly propagated 30 km to the southwest and 20km northeast. The rupture extended to surface of the earth. Two asperities (large slip areas) are identified. The maximum dislocation is about 2.3 m 25km southwest from hypocenter. The damage zone should extend to southwest direction due to the rupture propagation.

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. Gray lines represent the extent of the fault plane used in our inversion.

Snapshots


Figure : Snapshots of cumulative dislocation.

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.

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.

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

Last Updated: May 24, 2003