Sediment deformation in eastern Sagami Bay revealed by high-density seismic reflection survey

Abstract

Sagami Bay is known as a seismogenic area occurring large earthquakes repeatedly with M > 7 at the boundary between the Philippine Sea plate and the overriding northeastern Japan with the Quaternary sediments. To investigate this area for understanding the mechanism of repeated large earthquakes, we carried out a high density single-channel seismic reflection survey around Sagami Bay in April - May, 2005 using R/V Kaiyo of Japan Agency for Marine-Earth Science and Technology (JAMSTEC). We propose new growth scenario of a unique reverse fault associated with the 1923 Kanto earthquake in the Sagami Trough in this paper as follows from units of sedimentary layers of the seismic profiles provided tectonics information studies of the clear sedimentary facies is indicated along the Sagami Trough. In particular, the fault with reverse sense displacement of ENE-WSW strike is recognized in the Sunosaki Canyon. This reverse fault is located on the asperity of the large aftershock epicenter (M7.3) in the 1923 Kanto earthquake. There is no active fault in the seafloor of sedimentary layers from this reverse sense displacement to onshore. Thus, this displacement would be developed with the subducting Philippine Sea plate. We propose the growth process of obtained reverse sense displacement in Sagami Trough.