[S-SS14] 活断層と古地震

[SSS14-07] 三浦半島断層群および海域延長部（相模湾側）のマルチスケール反射法地震探査

*石山 達也¹、佐藤 比呂志^1,2、斉藤 秀雄³、石毛 宏和³、中田 守³、阿部 進³ (1.東京大学地震研究所、2.静岡大学防災総合センター、3.株式会社地球科学総合研究所)

キーワード：活断層、三浦半島、相模トラフ、反射法地震探査

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.