活断層研究
Online ISSN : 2186-5337
Print ISSN : 0918-1024
ISSN-L : 0918-1024
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北上低地西縁断層帯・南昌山断層群の断層変位地形と断層露頭
小坂 英輝楮原 京子今泉 俊文三輪 敦志吉田 春香齊藤 華苗儘田 豊
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2011 年 2011 巻 34 号 p. 13-22

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In this paper, we describe distribution and activity of the Nanshozan active fault group (F1, F2 fault) in detail, based on geomorphic feature and surface geology (Plio-Pleistocene Siwa Formation), including the active reverse fault passing through the first outcrop of the flexure (F3 fault). The Miocene strata have been thrust over the Siwa Formation along the mountain front (F1 fault). The F2 fault deforms fluvial terraces in the footwall of the F1 fault. Deformations of fluvial terraces and arrangement of valley spread of alluvial terraces (L2 surface) provide that the F3 fault runs through east side of the hills on the footwall of the F2 fault. Distribution of fluvial terraces indicates that the F1 fault has been inactive since the middle Pleistocene (H surface). Structure of the Siwa Formation indicates that the F2 fault has been formed since the middle Pleistocene (upper Siwa Formation). Studies of the surface folding and faulting of the fluvial terraces indicate a late Pleistocene vertical offset rate of 0.3 m/k.y. at the F2 fault and 0.05 m/k.y. at the F3 fault. Comparison of vertical offset rates of fluvial terraces provides that the primary fault activity is on the F2 fault.

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© 2011 日本活断層学会・活断層研究会
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