| Earthquake Research Institute, Univ. of Tokyo
2008 Iwate-Miyagi Nairiku Earthquake |
|---|
[Last updated 2008.06.15]
This is a preliminary finite fault model for the 2008 Iwate-Miyagi Nairiku earthquake which occurred at 08:43 on Jun. 14 (Japan local time, 23:43 on Jun 13 (UT)). Details may be revised when additional data become available.
We first analyzed the teleseismic P waves downloaded from IRIS-DMC to estimate the finite fault model assuming a point source at (latitude=N39.028 deg, longitude=E140.880 deg, depth=8 km) preliminarily announced by JMA. The result of this analysis indicates reverse faulting with possible two fault planes:
(Strike, Dip, Rake) = (203, 37, 93) or (19, 53, 88) [units in degree]
To choose an appropriate fault plane, we then estimated a slip distribution for each fault plane by minimizing the residuals between the observed and synthetic waves. The residuals for the two models, however, are not so different. We therefore choose the fault plane dipping westward, according to the aftershock distribution by JMA.
Figure 1 shows the resultant slip distribution, where slips are drawn in
a color scale. The arrows indicate the slip directions of the hanging wall
relative to the footwall. The yellow star denotes the hypocenter. The fault
plane is presumed to be 44 by 24 km, and the area of significant slip is
derived to be 25 by 16 km with the largest slip of 2.5 m. The seismic moment
and moment magnitude are estimated to be 2.0e19 Nm and 6.8, respectively.
(Strike, Dip, Rake) = (203, 37, 93) [The NW-dipping plane is chosen according to the aftershock distribution]
Seismic Moment = 2.0e19 Nm, Moment magnitude (Mw) 6.8
Maximum slip: 2.5 m
Fig.1 Slip distribution on NW-dipping fault plane.
Figure 2 shows a projection of the slip distribution onto the ground surface.
Gray circles indicate the locations of aftershocks determined by Hi-net
up to 18:00 on Jun. 14 (automatic determination). The rupture, initiated
at a point denoted by a star, mostly propagated toward the south. This
rupture propagation is also seen in the solution for the SE-dipping fault
plane.
Fig.2 Surface projection of the slip distribution for the NW-dipping fault
plane.
Fig.3 Comparison of the observed and synthetic seismograms for the NW-dipping
fault plane.