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Structure and development of the Sagami trough and the Boso triple junction |
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| Authors: | Yujiro Ogawa Tetsuzo Seno Hinako Akiyoshi Hidekazu Tokuyama Kantaro Fujioka and Hidetsugu Taniguchi |
| Institution: | 1 Department of Geology, Faculty of Science, Kyushu University 33, Hakozaki, Fukuoka 812, Japan 2 Earthquake Research Institute, University of Tokyo, Yayoi, Bunkyo, Tokyo 113, Japan 3 Department of Earth Sciences, Faculty of Science, Chiba University, Chiba 260, Japan 4 Ocean Research Institute, University of Tokyo, Minamidai, Nakano, Tokyo 164, Japan 5 Department of Earth Sciences, College of Humanities and Sciences, Nihon University, Sakurajosui, Setagaya, Tokyo 156, Japan |
| Abstract: | The Sagami trough is located at the particular plate margin where the Izu forearc is subducted underneath the Honshu forearc. At its southeastern end, the world's only known TTT-type triple junction (Boso triple junction) has developed. Several different kinds of basins occur in different segments along the Sagami trough and at the triple junction. The bathymetric, geologic, and geophysical data obtained during the Kaiko Project and from additional studies are summarized together with our onland studies. We suggest that the right-lateral oblique plate motion formed an eduction margin in the Sagami basin, while a normal subduction margin and an oblique subduction margin have been formed in the Middle Sagami trough basin. These tectonic phenomena resulted from the long-lasting compressional covergence between the Philippine Sea plate and Eurasian plate since the early or middle Miocene. The North basin on the northeasternmost margin of the Philippine Sea plate near the Boso triple junction has developed as a stretched basin due to the westward motion of the Philippine Sea plate with respect to the Eurasian plate. |
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