Rediscovery of the Hakuchi thrust associated with the Median Tectonic Line active fault system in Awa-Ikeda town, eastern Shikoku, southwest Japan

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  • KATO Hironori
    Aratani Civil Engineering Consultants CO., LTD.:Graduate School of Integrated Arts and Sciences, Kochi University
  • YOKOYAMA Shunji
    Research and Education Faculty, Kochi University

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  • 中央構造線活断層系に伴われる阿波池田町白地衝上の再発見

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In the western part of Ikeda town, Miyoshi City, Tokushima Prefecture, there remains an unsolved issue about the geological boundary between the Cretaceous Izumi Group and the Pleistocene Dochu Formation. Nakagawa and Nakano (1964) considered there is the Hakuchi thrust comprised of the Izumi Group as its hanging wall, but Okada (1968) argued this was a high angle right lateral reverse fault. Based on our field investigation on the distribution of the Izumi Group and the Dochu Formation elucidated by the layout of each outcrops and the discovery of fault gouge containing the material from the Sambagawa crystalline schist at their boundary, we made it clear that a thrust really exists between the Izumi Group and the Dochu Formation, and that the Izumi Group thrusts over the Dochu Formation at an average angle of 25 degrees from the north at this fault. Namely, we substantiated the existence of the Hakuchi thrust recorded by Nakagawa and Nakano (1964).

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