Shallow seismic reflection survey across the North Matsuda fault in the Kozu-Matsuda fault system, central Japan

Kimura Haruo, Sato Hiroshi, Ito Tanio, Miyauchi Takahiro, Matsuta Nobuhisa, Kawamura Tomonori, Ishiyama Tatsuya, Okada Shinsuke, Kato Naoko, Ogino Sumiko, Kagohara Kyoko, Oda Shin, Node Katsuya, Ikawa Takeshi

doi:10.11462/afr1985.2005.25_85

The North Matsuda fault in the Kozu-Matsuda fault zone is one of the active fault system, showing the largest vertical component of slip rate onshore Japanese islands. The Kozu-Matsuda fault system is considered as a part of the northern margin of the Philippine Sea plate. It is necessary to obtain the horizontal shortening component of slip rate of the North Matsuda fault for a better understanding of active tectonics in the northern margin of the Philippine Sea plate. To reveal the subsurface structure of the North Matsuda fault, high-resolution shallow seismic reflection survey with about 3.2 km line length was carried out across the fault, A kind of accelerated weight drop system named as Yuatsu Impactor (JGI Inc. ) was used as seismic source which has wide band frequency spectrum. Both the standard shot intervals and group intervals of geophones were 10 m. The Sakawa River near the center of the line obstructed both shooting and geophone setting, and the half of the line in the Matsudayama Mountains was severely crooked. Although such a bad survey conditions, the seismic section after careful data processing shows a drastic structural change and a north dipping thrust fault with 18 degrees near the Sakawa River, which is suggested as the North Matsuda fault. The fault trace revealed by a result of the seismic reflection survey is exactly located along the Sakawa River.

Shallow seismic reflection survey across the North Matsuda fault in the Kozu-Matsuda fault system, central Japan

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