HR: 1340h
AN: T43B-1350    [Abstracts]
TI: Fault model in the eastern margin of the Japan Sea based on the asymmetric topography profile of the oceanic ridges
AU: * Aoyagi, Y
EM: y-aoyagi@criepi.denken.or.jp
AF: Central Research Institute of Electiric Power Industry, 1646 Abiko, Abiko-shi, Chiba-ken, Abiko, 270-1194, Japan
AU: Abe, S
EM: shintaro@criepi.denken.or.jp
AF: Central Research Institute of Electiric Power Industry, 1646 Abiko, Abiko-shi, Chiba-ken, Abiko, 270-1194, Japan
AB: The eastern margin of the Japan sea is one of the major convergent zone in East Asia. In a past few decades several M7-8 earthquakes (1964 Niigata, 1983 Japan Sea, 1994 SW-off Hokkaido, and 2007 off Mid-Niigata) occurred in this zone. They were often followed by large tsunami, which indicated a vertical seafloor movement by faulting. As a result of such crustal movement since 3Ma, many oceanic ridges with asymmetric topography profile have been formed along the coast. Recent seismic reflection surveys displayed the existence of active faults at the base of the ridges. However the fault parameters such as dip angle, width, top depth are still unknown. We introduce a method to estimate the unknown parameters paying attention to the asymmetric profiles as following 3 steps: (1) Calculation of surface deformation pattern for various combinations of fault parameters based on the dislocation theory. The calculated profiles of the surface pattern are stored to a deformation database. (2) Extraction of the ridge profile from observed seafloor topography. (3) Retrieval of the best fitting model to the observed profile from the deformation database. As a result of investigation using SEABEAM data, highly correlated surface deformation pattern were found for most oceanic ridges in the eastern margin of the Japan Sea. The region between the Okushiri Island and the Oga Peninsula is dominated by east-dipping faults with a high angle, whereas the regions on either side to the north and south tend to be dominated by west-dipping faults with a low angle (20 to 50 degrees). We will propose a fault model, which can be referred in a seismic and tsunami hazard assessment.
DE: 3001 Back-arc basin processes
DE: 3025 Marine seismics (0935, 7294)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8107 Continental neotectonics (8002)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting