地震活動に関係した地殻変動(6) ―中部地方北西部の地震活動と神岡で観測された地殻変動―

Abstract

A sequence of shallow earthquakes alternated around 1959 in the Chubu district. Coinci-dentally, at the Ogoya observation station, the rate of ground tilts in the direction of the tectonicforce changed and the mode of the anomalous variation of ground tilts accompanied by the indi-vidual earthquakes also changed.A similar phenomenon was found in the mode of tilt variations at the Kamioka observationstation. It was confirmed that the change in the rate of gradual ground tilts appeared in the direc-tion of N45°W-S45°E from the fact that the acceleration of gradual tilting movements accumulatein this direction. It is a remarkable fact that this direction closely coincides with that of Ogoya(N25°W-S25°E).On the contrary, it has been ascertained that the tilt variation as see-saw motion correspondingto three active stages in the Kitamino earthquake series appears in the direction parallel to theAtotsugawa fault (N60°E-S60°W). In other words, it may be imagined that a see-saw motion withthe shorter period superposes on the gradual movements in the direction of N45°W-S45°E.