都市における応用地質学の課題 兵庫県美方地域の比抵抗構造

Abstract

CSAMT (Controlled Source Audio Frequency Magnet-Telluric) and TDEM (Time Domain Electromagnetic) survey were carryed out at Mikata area, northern part of Hyogo Prefecture. The joint inversion with CSAMT and TDEM was conducted, and the result is summarized as follows:(1) The resistivity structure of the Mikata area to 2000-3000m below the surface was analyzed.(2) The resistivity structure to 500m below the surface was analyzed with CSAMT. TDEM data was used to analyze the deeper structure.(3) In a shallow zone to 250m below the surface the high resistivity zone with more than 200Ω-m is distributed around the northwest of Yatagawa River. And the low resistivity zone with less than 200Ω-m is around the southeast side. This resistivity structure corresponds to the Utaosa rhyolite lava around the northwest side of the river and Haruki mudstone member around southeast side.(4) The low resistivity zone with less than 50Ω-m, intersecting this structures, under 500m below the sea level, is stretching from east-northeast to west-southwest.(5) That low resistivity zone corresponds to the discharge area of the hot water at Mikata area, and is considered to indicates the presence of the fractured rock (granitic rock) in deep underground. The points of the hot springs may be controlled by the presence of the deep low local resistivity zone.