Some Results from Measurements of the Geomagnetic Field and the Electrical Resistivity in the Izu-Tokai Region, Japan

Abstract

Repeated surveys of the geomagnetic total intensity, which have been carried out in the northeastern part of the Izu Peninsula, disclosed anomalous secular changes in the total intensity. The spatial distribution of the anomalous changes is in good agreement with that expected from piezomagnetic fields associated with stress accumulation in the crust which is inferred from crustal uplift in the survey area. Measurements of geomagnetic variations of short period have also been carried out at a station located in the uplift region, in order to detect crustal resistivity changes by analyzing inductive response of the crust to short-period geomagnetic variations. The observed anomalous secular changes in the amplitudes of horizontal components of short-period variations were found to be well correlated with time-dependent nature of the crustal uplift, whereas preliminary results of transfer function analysis reveal no anomalous change in the vertical component. It is concluded, therefore, that the resistivity underwent a change in the crust near the station, presumably in the uplift area.