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


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Joint Inversion was made using teleseismic data (provided by IRIS-DMC) and Strong ground motion data (provided by NIED)

On July 26, 2003 (JST), a reverse-faulting earthquake (Mjma = 6.1) 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 in northeast of Honshu. I retrieved teleseismic body waves (P-waves) and strong ground motion data recorded at IRIS-dmc stations and K-net (NIED) via Internet, respectively.

Result

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

Fault model 1:
The seismic moment Mo = 1.4 x 10**18 Nm (Mw 6.0);
The source duration T = 7 s;
(strike, dip, rake) = (10, 42.5, 90)
Hypocenter: (Lat. = 38.389N, Lon. = 141.191E, depth = 6 km).
[The epicenter of the main-shock was determined by NIED]
Maximum slip = 1.1(m)

Fault model 2:
The seismic moment Mo = 1.1 x 10**18 Nm (Mw 6.0);
The source duration T = 7 s;
(strike, dip, rake) = (10, 42.5, 92)
Hypocenter: (Lat. = 38.389N, Lon. = 141.191E, depth = 6 km).
[The epicenter of the main-shock was determined by NIED]
Maximum slip = 1.1(m)

The main rupture mainly propagated 8 km to the north. The maximum dislocation is about 1 m. It is very remarkable that the source areas for largest fore-shock and after-shock were almost free from coseismic moment release of the main-shock. This implies that those areas took a part of barriers to dynamic rupture in the main-shocks.

(Yagi, IISEE, BRI, 2003)





Fault Model 1

Map View


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

Slip distribution and source time function


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

Waveform comparison and station map (Strong ground motion)


Figure : Comparison of the observed waveform (Black) with the calculated waveform (Red). The numbers below the station code indicate maximum amplitude in cm/sec. The start time of the traces is lined-up at 5 (s) before the P-wave arrival.

Waveform comparison and station map (Teleseismic)


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.




Fault Model 2

Map View


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

Slip distribution and source time function


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

Waveform comparison and station map (Strong ground motion)


Figure : Comparison of the observed waveform (Black) with the calculated waveform (Red). The numbers below the station code indicate maximum amplitude in cm/sec. The start time of the traces is lined-up at 5 (s) before the P-wave arrival.

Waveform comparison and station map (Teleseismic)


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.


Station Map



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.


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

Last Updated: May 27, 2003