中央構造線(紀伊半島中央部)の電磁気的構造調査

Abstract

Electromagnetic surveys of the Median Tectonic Line (MTL) were carried out at the central part of Kii Peninsula by VLF- and ELF-MT methods to know underground structure of the MTL. One-dimensional resistivity structures at eight sites were determined along two lines (the West line and the East line) across the MTL.We found some differences of electromagnetic structure between the West line and the East line. The West line approves the existence of a highly resistive (>2000 Ωm) layer below the surface layer which is less resistive, being 20-60 meters in thickness on the north side of the MTL. At the opposite side of the MTL, all layers except two layers show low resistivity of about 20-400 Ωm. As for the East line, a highly resistive layer of some thousands Ωm was confirmed below the surface layer of about 120-550 Ωm at all observation sites. A lineation of very low resistive layers is found on the south side of the MTL in both the measuring lines. The resistivity gap along the West line is caused by the different geological setting; Ryoke granite is widely distributed on the north side of the MTL and crystalline schist belonging to Shimanto belt is common on the south side of the MTL. The lineation of low resistive layers can be explained by existence of underground subfaults of the MTL.