Regional characterization of the crust in metropolitan areas, Kanto and Kinki, Japan.

Abstract

Deep seismic profiling was performed in the Kanto and Kinki areas for 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 (PSP). The depth to the top of this plate, 4 to 26 km, is much shallower than previous estimates based on the distribution of seismicity. This shallower plate geometry changes the location of maximum finite slip of the 1923 Kanto earthquake and its location corresponds to a zone of poor in reflection on the mega-thrust. Namely, a strong reflectivity zone along the mega-thrust coincidence with an aseismic slip zone. The existence of the PSP slab beneath the Kofu basin was confirmed by north-dipping strong reflections at 30–40 km in depth. In the Kinki area, a 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 16 km in depth. The shallower reflectors correspond to the base of seismogenic zone. Dipping reflectors, probable deeper extension of active faults merges the mid-crustal reflectors