Active deformation of Sagami Bay triggered by approach of the Izu island arc

Sagami Bay in central Japan is known as the seismogenic and tsunamigenic zone of the 1703 and 1923 Kanto earthquakes that caused devastating damage in the Tokyo metropolitan area. However, the tsunamigenic structure within the frontal wedges of the subduction zone remains unresolved after the last disastrous events. In the present study, the detailed structural features of the shallowest structure of the Sagami Tectonic Line in Sagami Bay were revealed by seismic reflection, a deep-towed high-resolution sub-bottom profiler, and swath bathymetry data. Based on our data, the middle segments of the Sagami Tectonic Line, which is distributed along the southwestern rim of the Miura Knoll, are considered highly likely to be an active fault that has been a repeatedly active feature. The trough-fill sediments of the south Sagami Bay are currently thought to be actively deformed by the compressive stress accompanying northwestward subduction of the tip of Izu-Ogasawara (Bonin) Arc crust on the Philippine Sea plate.