Preliminary Results of Rupture Process for 2003 December 22 CENTRAL CALIFORNIA, earthquake


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

On December 22, 2003 (GMT), a thrust-faulting earthquake (Ms 6.5) occurred in central California USA. I retrieved teleseismic body waves (P-waves) data recorded at IRIS-dmc stations via Internet. 20 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

Fault model 1

The seismic moment Mo = 8.0 x 10**18 Nm (Mw 6.5);
The source duration T = 12 s;
(strike, dip, rake) = (115, 40, 91)
Hypocenter: (Lat. = 35.706‹N, Lon = 121.102‹WN, depth = 7.6 km).
[The epicenter of the main-shock was determined by USGS]
Variance: (obs-cal)**2/obs**2 = 0.30596
Maximum slip = 2.4(m)

Fault model 2

The seismic moment Mo = 8.8 x 10**18 Nm (Mw 6.6);
The source duration T = 12 s;
(strike, dip, rake) = (297, 50, 92)
Hypocenter: (Lat. = 35.706‹N, Lon = 121.102‹WN, depth = 7.6 km).
[The epicenter of the main-shock was determined by USGS]
Variance: (obs-cal)**2/obs**2 = 0.29991
Maximum slip = 2.2 (m)

The difference of variances for two fault models is too small to judge which is an actual fault plane.

The rupture mainly propagated 15 km to the southeast from hypocenter. The rupture may extend to surface of the earth. Two asperities (large slip areas) are identified.

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, BRI, 2003)


Distribution of fault-slip (model 1)



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 (model 1)



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

Waveform comparison (model 1)


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.


Distribution of fault-slip (model 2)



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 (model 2)



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

Waveform comparison (model 2)



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., A. Nishitani and M. Matsu'ura, Geodetic data inversion using ABIC to estimate slip history during one earthquake cycle with viscoelastic slip-response functions, Geophys. J. Int., accepted 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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If you have questions, please send to yagi@kenken.go.jp.

Last Updated: December 24, 2003