宝立における電磁気観測

Abstract

Since 1987, the total geomagnetic force and the earth's electric potential have beenobserved at the Horyu station in the pointed area of the Noto Peninsula, which projects intothe Japan Sea. The magnetic and electric data of the Horyu station were compared withthose of the other stations in the Hokuriku districts, and with those of the Kakioka station inthe Kanto districts. The following results were obtained.1. The simultaneous variation of the amplitude of total magnetic field at each station witha period between five and a few tens of minutes was recorded and compared. There existsa tendency for the amplitude of variation to increase as the observation site becomes furtherfrom the Japan Sea. Sasai (1969) analyzed the vertical component of geomagnetic fieldobserved at the several stations around the Kii Peninsula, which also projects into the PacificOcean. He suggested that the vertical component decreases according to the distance fromthe Pacific Ocean. The inverse trend of geomagnetic field in the regions close to the JapanSea and the Pacific Ocean was interpreted as the effect of induced magnetic field by sea water, introducing the schematic model of the "Island Effect".2. The maximum direction (MD) of the induced earth currents around the Horyu station wasobtained, using the data from the disturbance of geomagnetic field and/or lightning aroundthe station. A MD of N15' W was determined. In the case of active faulting as theAtotsugawa fault (Nakayama et al., 1987) and the Kurobishiyama fault, the MD vector wasobserved perpendicular to the azimuth of each fault. This was interpreted as the effect of thefracture zone of the fault having a low resistivity. The schematic model was introduced toexplain the MD for induced electric potential in the low resistivity area.