ON THE PECULIAR MODE OF CRUSTAL MOVEMENTS ACCOMPANIED WITH THE ACTIVITIES OF SHALLOW EARTHQUAKES

Abstract

Since 1937 the continuous observations of the crustal movements with tiltmeters and extensometers have been carried out at twenty observing stations in Japan. From the results of tiltmetric observations it was found that the ground tilt relating to the occurrence of earthquakes proceeded generally through three stages. In the first stage, the ground tilt generally proceeded in the direction of operation of geotectonic force which caused the horizontal displacement of the ground at the observing station. In the second stage, it was prominent in the direction towards the epicentral region. In the third stage, just before the occurrence of earthquakes, the ground tilt generally increased its speed or reversed the sense of its direction.