Observed Secular Tilting Motion of the Ground which Preceded the Occurrence of Several Destructive Earthquakes

Abstract

Some details of tilting motion of the ground continuously observed for a long period with the aid of the highly sensitive, fused-silica tiltmeter of horizontal pendulum type at the Kamigamo Geophysical Observatory is described in this paper, with regard especially to the secular ground-tilting in connection with seismic activity in the surrounding area of the Observatory. It was consequently clearly ascertained, after the careful examination and perfect exclusion of various disturbing effects, that the ground commenced a characteristic tilting motion downward to the direction of the epicenter several months before the occurrence of the destructive earthquakes, and showed a recovering motion after the quakes, so far as the present cases of the five destructive earthquakes around the Observatory concern.