Continuous Observations of the Ground Deformations Related to the Matsushiro Earthquakes

Abstract

In order to investigate the relations between ground deformations and seismic activities in Matsushiro and neighbouring regions, continuous observations on the ground tilt and strain were carried out at Matsushiro and Suzaka. At Matsushiro, three tiltmeters of horizontal pendulum type and two extensometers of bow-string type were installed in the underground gallery bored into Zozan hill, the western suburb of Matsushiro Town. At Suzaka, two tiltmeters of water tube type and two tiltmeters of horizontal pendulum type were installed in the underground gallery bored halfway up Kamatayama hill, the western suburb of Suzaka City. As to Matsushiro, it was observed that the velocity of the ground tilt sometimes changed before the occurrence of an earthquake. As to Suzaka, it proved that the direction of the ground tilt changed markedly every time an earthquake of a magnitude larger than 5.0 occurred, and an anomalous ground tilt appeared before the occurrence of the earthquakes of Sep. 27, 1966, and Feb. 8, 1967.