開析ペディメントにおける花こう岩類の風化帯構造 : 広島市西部の深層風化帯について

概要

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The deep weathered region of the granitic rocks in the western part of Hiroshima-city coincide with the dessected pediment geomorphologically which was studied in detail by Akagi Y. (1962). In this paper, the author has made clear the following points from an analysis of p-wave velocity, N-value profile and geomorphological development. (1) The deep weathered zone in this region is composed of two mirage layers which is given a name respectively "the upper weathered zone" and "the lower weathered zone" for a distribution of P-wave velocity. Each zone is characterized by the constant rate of increase for P-wave velocity and N-value. (2) The primary sheeting joint (P・S・J) and the secondary sheeting joint (S・S・J) descrived by previous paper, Hashikawa, et al (1974) develope respectively in the lower weathered zone and the upper weathered zone. (3) The P・S・J develope almost parallel to the horizontal or slightly inclined land surface of pediment and to the unweathered bed rocks. The other hand the S・S・J is almost parallel to the convex land surface of the dessected pediment. (4) The structural development history of the weathered zone is divided to 5 stages in Fig. 9.
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