Geomagnetic induction study of the seismically active fault along the southwestern coast of the Sea of Japan.

Abstract

Geomagnetic and telluric current observations were conducted on and around the seismically active fault, Yoshioka-Shikano Fault, from 1976 to 1977 The confined plane of the geomagnetic variation expressed as 4Z=A4X+Bd fir, was calculated for each station by applying the transfer-function techniques or the least-square method to the records of Pi 1-2 type pulsations.It was found that the landward increasing tendency of the A values of the confined planes caused by the electromagnetic coastal effect of the Sea of Japan, was slightly interrupted on the northern edge of the fault and also, that the amplitude of the N-S component of geomagnetic variation (4X) was considerably enhanced upon the fault. These results are proposed to be due to the effect of the swelling of the electrically conducting medium in the crust beneath the seismically active fault.A tentative analysis was also made for the telluric current records observed on the fault, comparing it with the data obtained at the same site just after the Tottori Earthquake. As for the direction of polarization of the electric field there was no noticeable difference between them.

Two-dimensional modelling of resistivity structure beneath the Tohoku district, northern Honshu of Japan, by a finite element method.

“…MIYAKOSHI and SUZUKI (1978) and NISHIDA (1982) proposed resistivity models in southwestern Japan and southern Hokkaido, respectively. Their models are characterized by the swelling of the conductor inside of the volcanic front.…”