High-resolution seismic reflection survey results in the eastern coastal area of Boso Peninsula, Central Japan

Abstract:

GSJ has conducted the coastal project since 2008 in order to equip seamless geoinformations of land and sea. This project has approached the eastern coastal area in Boso Peninsula, eastern part of the Kanto region, Japan. In the waters off the Boso Peninsula, the Philippine Sea plate subducts under the Honshu arc. Therefore, the subsurface structure in this area is important for understanding of tectonics of Kanto region, Japan. In this study, we obtained seismic sections of ca. 1100 km in total length with a boomer and multi-channel streamer (24 channel with 3.125 m spacing) and report the geological significance of the subsurface structure in the area.

We mainly research the Kujukuri area, eastern part of Boso peninsula. The broad shelf characterizes this area and that width is ca. 50 km. A clear unconformity can be distinguished separating two strata and we define them as the Kujukuri A Unit and the Kujukuri B Unit, in ascending order. The planner stratification characterizes the Kujukuri A Unit and this unit buries many channels. Distinct stratification deformed by synclines and anticlines develops in the Kujukuri B Unit. The amounts of displacement of them are over 50 msec (TWT) and it exceeds 100 msec in some locations. Additionally, a lot of faults develop in the Kujukuri B Unit near land and the vertical amounts of displacement of faults exceed 100 msec.

These structures in the Kujukuri B Unit might have an effect on tectonics of the Kanto region. The understanding of geology in the Kujukuri area contributes to the tectonics of Japan.