Preliminary Results of Rupture Process for July 15, 2003 CARLSBERG RIDGE Earthquake

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

On May 21, 2003, a right-lateral strike slip earthquake (Mw = 7.7) occurred near Carlsberg ridge, where the plate boundary between the African plate and the Indian plate. I retrieved teleseismic body waves (P-waves) data recorded at IRIS-dmc stations via Internet. 15 stations were selected from the viewpoint of good coverage, and used in the waveform inversion with ABIC (Fukahata et al., 2003a; Fukahata et al., 2003b; Yagi et al., 2003).


The seismic moment Mo = 4.1 x 10**20 Nm (Mw 7.7);
The source duration T = 85 s;
(strike, dip, rake) = (37, 80, -177)
Hypocenter: (Lat =2.56S, Long = 68.30E , depth= 15 km).
[The epicenter of the main-shock was determined by USGS]

The source process is characterized unilateral rupture propagation. The rupture propagated 150 km to the northeast. The rupture extended to surface of the earth. One asperity (large slip areas) are identified. The maximum dislocation is about 11.5 m at 125km northeast from hypocenter.

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.

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.


Fukahata, Nishitani and Matsu'ura, Geodetic data inversion using ABIC to estimate slip history during one earthquake cycle with viscoelastic slip-response functions, Geophys. J. Int., submitted, 2003a.

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, 2003b.

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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Last Updated: 2003 July 16