近畿地方北西部地域の活構造 (4)

Abstract

Geological, geophysical and hydrogical surveys were carried out in the westward extended area of the Yamada fault. The Yamada fault is well known as a seismic fault occurred at Tango earthquake (March 7, 1927: M 7.5) as well as that of the Go-mura fault. From geological and hydrogical surveys, some remarkable outcrops, topographical evidences and mineral springs which show the existence of the fault were found in the surveyed area, especially Izushi-Cho, Hyogo Prefecture. The hidden fault was traced by gamma-ray and ELF-MT soundings. Gamma-ray intensity was measured at three sites at Izushi-Cho. Resistivity surveys by a ELF-MT method were conducted in the two sites. The spatial distribution of the obtained gamma-ray intensities and apparent resistivities reveals the existence of high intensity and low resistivity belts along the fault which was inferred form the other surveys. These belts have a width more than 1km in a direction of N70-80°E and a width of some hundred meters in a direction of N70°W.The results of these surveys show that this fault system was followed from the Yamada fault to the west of Izushi-Cho. This fault system bounds this region into two blocks, as Hokutan and Maizuru blocks.