HR: 1340h
AN: S13B-0205    [Abstracts]
TI: Fault Plane Determination for the 1964 Niigata Earthquake Using Tsunami Simulations
AU: * MORITA, M
EM: morita@eqh.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasyo, Uji, Kyoto, 611-0011 Japan
AU: MORI, J
S13B-0205 AF: Disaster Prevention Research Institute, Kyoto University, Gokasyo, Uji, Kyoto, 611-0011 Japan
AB: The 1964 Niigata earthquake (Ms 7.5) occurred off the Japan Sea coast of Honshu, Japan, with a 4 m tsunami that caused significant damage. The earthquake is important for understanding the seismic hazards along the Japan Sea coast and also for understanding the tectonic boundary between the Eurasian and North America plates. This earthquake was located fairly close to the coast, yet the orientation of the fault plane has not been clearly determined. The focal mechanism has been well constrained to be a thrust solution striking approximately north, with one nodal plane dipping steeply toward the west and the other dipping at a low angle toward the east (Hirasawa, 1965; Abe, 1975; Mori and Boyd, 1985). In this study, we calculate sea bottom deformation for assumed models with fault plane dipping toward the west and toward the east, and simulate tsunami wave caused by these deformations. We used teleseismic P waveforms to determine the slip distribution for the earthquake. We assumed two fault planes for the earthquake. Fault 1 has a strike of 9°E and a dip of 25°to the east, and Fault 2 has a strike of 189°E and a dip of 65°to the west. To estimate slip distributions on these assumed fault planes, we inverted the waveforms from 10 stations, well distributed in azimuth around the earthquake. Using the derived slip distribution for each fault plane, we calculated the ground (sea bottom) deformation by the method of Okada (1992). This deformation was used for the tsunami simulation. Our results show that the large area of subsidence, fairly close to the Honshu coast, in the model for Fault 2 (westward dip) is very similar to the tsunami generation area obtained by back-projecting the tsunami arrival times (Iida, 1968). Also, the relative arrival times of the tsunami for the close stations along the Honshu coast compared to the arrivals at Sado island, match the model for Fault 2 better than for Fault 1. There is limited tsunami waveform data for the close stations, but we were able to examine the polarity of the initial tsunami wave at the station, Matsugasaki. The observed data shows a positive first motion which is consistent with the model for Fault 2. The model for Fault 1 (eastward dipping) shows a downward first motion. These results indicate that the fault plane for the 1964 Niigata earthquake dips toward the west.
DE: 4564 Tsunamis and storm surges
DE: 7200 SEISMOLOGY
SC: Seismology [S]
MN: Fall Meeting 2005