著者

渡辺 満久

出版者

日本活断層学会

雑誌

活断層研究 (ISSN:09181024)

巻号頁・発行日

vol.2016, no.44, pp.1-8, 2016-03-31 (Released:2016-10-21)

参考文献数

18

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There are several marine terrace surfaces in the southeastern part of Shimokita peninsula, northeast Japan. They are classified into H1, H2, M1, M2 and M3 surfaces in descending order. The M1 and M2 surfaces are correlated with those formed in MIS 5e and in MIS 5a, respectively. The Rokkasho fault merging into the extensive submarine fault along shelf edge in the north has successively deformed these terrace surfaces, resulting in a 1-2 km wide flexural scarp tilting to the east on the M1 and M2 surfaces. Vertical offset of the M1 surface is over 30 m in the north and less than 20 m in the south. The flexural scarp extends at least 15 km to the south of the Takahoko Lake. The Detoseiho fault is a subsidiary branch fault of the Rokkasho fault developed in the Rokkasho flexural scarp. Because the M1 surface is bending toward the east (toward the coast), the sand layer composing of the M2 surface abutted on the monocline slope. Following movements of the Rokkasho fault have deformed the M2 surface in the same direction as the M1 surface, and consequently the M1 and M2 surfaces converged upon in the flexural scarp. This makes it very difficult to distinguish one from the other. Such geomorphic development should be strongly controlled by the activity of active fault differentiating tectonic relief and the width of flexural scarp reflecting the depth of tip of fault plane. Further examinations on active faults extending parallel to the coast lines are required to solve the problems.