[S-SS14] Active faults and paleoseismology

[SSS14-07] Multi-scale seismic reflection profiling across the Miura Peninsula fault system and its western extension in the Sagami Bay

*Tatsuya Ishiyama¹, Hiroshi Sato^1,2, Hideo Saito³, Hirokazu Ishige³, Mamoru Nakata³, Susumu Abe³ (1.Earthquake Research Institute, the University of Tokyo, 2.Center for Integrated Research and Education of Natural Hazards, Shizuoka University, 3.JGI, Inc.)

Keywords:Active fault, Miura Peninsula , Sagami Trough, Seismic reflection profiling

We acquired onshore and offshore multi-scale seismic reflection data across the Miura Peninsula fault system and its western extension in the Sagami Bay, to define their subsurface geometries, along-strike distribution, and recent activities offshore faults. Onshore, 16-km-long multichannel seismic reflection profile using two vibroseis trucks illuminate fault and basin structures to depth of 5 km, indicating that Takeyama and Kitatake Fault dip northward and Minamishitaura fault dip southward steeply, respectively. Considering across-strike their close spacing, Takeyama and Kitatake Fault merge into a single fault plane at a shallow crustal level. As indicated by AIST (2021) , these strike-slip fault system seemingly extend to the Sagami Bay to the west. Our high resolution seismic reflection profiles clearly indicate along the fault traces identified by AIST (2021) offsets and deformation of sea floors on the continental shelf and/or underlying Holocene sediments are identified, indicating recent fault activities. Styles of deformation identified by our seismic data also indicate that strike-slip components are dominant along these offshore active structures, similar to the Miura Peninsula fault system. These results strongly suggest onshore and offshore strike-slip faults in the Sagami Bay, Miura Peninsula, and Tokyo Bay comprise a series of longer strike-slip fault system. In our presentation, we also discuss recent offshore fault activities and deeper fault structures based on higher resolution seismic reflection profiles and reprocessed onshore-offshore MCS data, respectively.