Finite-Fault Stochastic Simulation of the 2008 Iwate-Miyagi Nairiku,
Japan, Earthquake
Abstract
Finite-fault stochastic method was applied to simulate the Mw 6.9, 2008
Iwate-Miyagi earthquake at 44 selected Kik-net sites using EXSIM
computer code. To investigate the effects of source characteristics on
the simulated results, three models were considered: two models with
prescribed slip distribution (Model 1 and Model 3) and a model with
random slip distribution (Model 2). S-wave regional attenuation
indicates obvious difference between fore-arc and back-arc regions which
are formed by volcanic front. Site amplification was determined by
corrected surface to borehole spectral ratio and Quarter wavelength
methods. High frequency decay parameter (kappa) was estimated to be
0.0473 s. The value of 160 bars for stress drop was calculated by
minimizing absolute residual of 5% damped pseudo spectral accelerations
(PSA). Comparison of the observed and simulated peak ground
accelerations and PSAs were performed to investigate the capability of
our finite-fault models. The residual models represent that the
simulated results by Model 2 are in good agreement with the observations
in f < 3 Hz, while the other models can better simulate higher
frequency motions. We also focused on the effects of slip patches
sitting on the fault plane on near-field stations placed in the
directions of slip propagation. For these stations, the simulated
results by Model 1 and Model 3 were preferred over those of Model 2.
Finite-fault models successfully interpreted the real forced motion to
AKTH04 where the recorded peak values were abnormal for
non-seismological reasons. Finally, the comparison of intensity measures
with the GMPEs showed good agreement.