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