飛彈跡津川断層における地電流観測

特に地震時における地電流擾乱

抄録

Earth current can be observed as potential difference between two points. Commonly, earth current changes with geomagnetic field, magnetic storm and so on, while this current will show unusual change when shock occurs. The observation of earth current has become one of the most effective measures for the earthquake prediction in China. From this point of view, we have been observing earth current at the Atotsugawa Fault, one of the first class active faults in Japan, since 1976, to make clear the relation between earthquake and earth current. A local shock (M:3.6) broke out at 4:55 a.m. on September 16, 1978. The epicenter was located on the Ushikubi fault, parallel to the Atotsugawa Fault, 7 km northwest from Amo observatory point. About an hour before this shock occurred, a disturbance of the earth current started to be observed at the parallel component set along the fault. Almost at the same time as the shock occurred a disturbance began at the cross component. These disturbances of both components were the same pattern. The degrees of variations were 4mV (parallel component) and 2.5mV (cross component). In order to make clear the disturbance when the shock broke out, discussed the influence on earth current by examining the data of magnetic field, magnetic storm, rainfall and thunder. We used the data between 1978 and 1980. Judging from this result, these disturbances were considered to be related with the occurrence of shock on September 16, 1978. If these disturbances occurred as the result of the shock, we might explain this mechanism as follows: the disturbance of earth current which changes quickly first and then recovers slowly was caused by flowing of water in the process of dilatancy. This fact clearly shows the nature of diffusion of water.