男鹿半島の南方に見いだされた海底活断層

抄録

I re-analyzed the seismic profiles on west of Akita city, which were surveyed by Hydrographic Department of Japan in 1982. Buried active faults which deformed alluvium were recognized on the area. These faults are distributed in the same strike in echelon within a few kilometers. They are regarded as segments of one fault system (south of Oga peninsular fault, tentative name). The fault system is about 20 kilometers in length. Average rate of the fault displacement is estimated at 0.9 to 1.0 m/ky., based on the assumption that the basement of alluvium is 18,000 year before the present. Assuming that the acoustic reflectors in alluvium indicate event sediments by the past earthquakes, estimated recurrence interval of the fault is two thousand and a few hundred years, and the latest event was occurred about two thousand and a few hundred years ago. The magnitude of the earthquake is estimated to be M=7.0 based on the method proposed by Matsuda(1975).