阿讃山地北麓の断層地形

概要

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The studied areas are two; the midstream area of the Kôtô River and the Saida River area in the northern foot of the Asan Mountains, Shikoku. The geomorphic surfaces distributed in the two areas can be classified into four groups, namely H, M, L1 and L2 surfaces. The H and M surfaces were formed as fans overlying the Pliocene Mitoyo Formation. These fan deposits consist of weathered boulder gravels. The L1 and L2 surfaces are distributed only along the Saida River: the deposits underlying the two surfaces are not so weathered compared with the cases of the H and M surfaces.In the studied area, there are some major faults of east-west trend and minor faults north-south trend and these faults divide this region into east-west belts or blocks. The faults were active during the deposition of the Mitoyo Formation. But after the H surface was formed, the faults became inactive except the Nagao (N. F. in Fig. 1, 2), the Ayutaki (A. F.) and the Iwasaki (I. F.) Faults. The Ayutaki Fault dislocated the H surface and the west part of the Nagao Fault dislocated the M surface.The southern foot of the Asan Mountains is bordered by the Median Tectonic Line, many opinions about the fault topography having been presented. The comparative study on the faults in both sides of the Asan Mountains will be made in future.
東北地理学会の論文