MICRO-EARTHQUAKES OCCURRING IN THE VICINITY OF KYOTO (1)

Abstract

For the purpose of throwing the light on the nature of micro-earthquakes occurring in the vicinity of Kyoto, the routine observation was set about on Oct. 1963 at six observation stations founded newly in Kyoto, Osaka and Shiga Prefectures. The seismographs used are of vertical type with the maximum magnification of about 40, 000 for vibration of 0.4 sec. According to the analysis of data obtained until Mar. 1964, the epicenters of micro-earthquakes are almost located in a belt-like region running from Wakasa Bay to Osaka Bay with the width of about 25 km. As for the focal depths, most of them belong to the crust. The fact that the micro-earthquakes occurred concently in the belt-like region might be due to the tectonic structure of the region as deduced from the behaviour of gravity anomaly there. In addition, the magnitude of the micro-earthquakes treated here are estimated to range from 1 to 3.