RESEARCH ACTIVITIES IN 1998
Simultaneous Simulation Experiments during 2nd International Symposium on
Effects of Surface Geology on Seismic Motion
LOC of Japanese Working Group on Effects of Surface Geology (JWG-ESG) on
Seismic Motion, Association for Earthquake Disaster Prevention, planned the
special session on the Simultaneous Simulation for Kobe and Osaka area
during the 1995 Hyogoken-nanbu (Kobe) earthquake during the 2nd
International Symposium on ESG, which will be held on Dec., 1998, in
Yokohama Irikura, Kawase, and Iwata are the member of the LOC. Purpose of
the simultaneous simulation (SS) is to compare each other the simulated
synthetics submitted by numbers of participants from all over the world for
Kobe earthquake as examples, to understand the key parameters for
quantitative prediction of strong ground motions, and to find future horizon
of researches related to the ESG study and strong motion prediction.
The strong motion data and underground structure information are collected
and distributed to the participants. The target sites at which participants
are requested to calculate their own synthetics are specified by the
organizer. Members of our research group strongly cooperated to collect the
distributed data for SS and now are summarizing the results of SS test for
Kobe to realize the status of our prediction methods and how we can improve
our simulation methods.
US-Japan Cooperative Research on Near-Source Ground Motion and Earthquake
Damage
Prof. Irikura with others did the cooperative research on Near-Source Ground
Motion and Earthquake Damage with Dr. Somerville and Prof. Anderson group.
In this project, we mainly studied (1) scaling of heterogeneous fault models
from inversion results, (2) modeling of underground structure, and (3)
Theoretical ground motion modeling based on hybrid Green function method.
On the theme (1), we compiled source models by waveform inversion andcharacterized the heterogeneities of the source parameters such as asperity
size, number of asperities, etc, to obtain the scaling relation of them. On
the theme (2), we conducted array microtremor measurements at Reno basin to
estimate S-wave velocity structure of sedimentary basins. This exploration
method has established in Japan and widely used in many basins in Japan.
Moreover, we have already experienced the microtremor measurements in L.A.
basin and San-Fernando valley. We succeeded to obtain the S-wave velocity
structure of the superficial layers and showed the applicability of this
microtremor array measurements in Reno basin. On theme (3), we simulated
ground motions in near-source area during the 1994 Northridge and the 1995
Kobe earthquakes to check the validity and applicability of the hybtrid
Green function method. We now started to predict (post-dict) ground motions
during the 1948 Fukui earthquake which was one of the most heavily damaged
earthquake before the Kobe in Japan.
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