Preliminary Results of Rupture Process for May 27 2003 Near East coast of Honshu, Japan, earthquake


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

On May 26, 2003 (JST), a thrust-faulting earthquake (Mjma = 7.0) occurred in near east coast of Honshu, Japan, where the Pacific plate subductes west beneath the northeastern Japan island arc at rate of about 80 mm/year (DeMets et al., 1990, 1994). The depth of hypocenter and focal mechanism show that this earthquake is a typical intra-plate earthquake. 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., 2003; Yagi et al., 2003).

Result

Fault model 1

The seismic moment Mo = 3.8 x 10**19 Nm (Mw 7.0);
The source duration T = 16 s;
(strike, dip, rake) = (6, 21, 86)
Hypocenter: (Lat. = 38.817N, Lon. = 141.654E, depth = 70 km).
[The epicenter of the main-shock was determined by NIED]
Variance: (obs-cal)**2/obs**2 = 0.24177
Maximum slip = 2.1(m)

Fault model 2

The seismic moment Mo = 4.0 x 10**19 Nm (Mw 7.0);
The source duration T = 16 s;
(strike, dip, rake) = (193, 69, 87)
Hypocenter: (Lat. = 38.817N, Lon. = 141.654E, depth = 70 km).
[The epicenter of the main-shock was determined by NIED]
Variance: (obs-cal)**2/obs**2 = 0.23335
Maximum slip = 1.7 (m)

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

The aftershocks distribution determined by Hi-net (NIED) shows the fault model 2 is the proper model.

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)


Comparison between fault slip and aftershocks



Figure : Hypocenter determined by Hi-net (NIED).

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 NIED. Gray 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

DeMets, C., R. Gordon, D. Argus, and S. Stein, Current plate motion, Geophys. J. Int., 101, 425-478, 1990

DeMets, C., R. Gordon, D. Argus, and S. Stein, Current plate motion, effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motion, Geophys. Res. Letters, 21, 2191-2194, 1994.

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 27, 2003