Seismic Reflection Profiling in the Kanto and Kinki Metropolitan Areas, Japan

概要

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Deep seismic profiling was performed in the Kanto and Kinki areas to obtain a better estimation of strong ground motions. In the Kanto area, we identify the seismogenic source fault on the upper surface of the Philippine Sea plate. The depth to the top of this plate, 4 to 26 km, is much shallower than previously estimated from the distribution of seismicity. This shallower plate geometry changes the location of the maximum finite slip of the 1923 Kanto earthquake, and its location corresponds to a zone of poor reflection on the mega-thrust, namely, a strong reflectivity zone along the mega-thrust coincidences with aseismic slip zone. In the Kinki area, 120-km-long seismic reflection profiling was carried out from Osaka to Suzuka across the Osaka and Ise basins and several active faults. Deep sub-horizontal reflectors are found at 26 and 16km in depth. The shallower re flectors correspond to the base of the seismogenic zone. Dipping reflectors, probably deeper extensions of active faults, merge into the mid-crustal reflectors.