Seismometric Observations of Matsushiro Swarm Earthquakes

This paper is the report of seismometric observations of Matsushiro swarm earthquakes made by Abuyama Seismological Observatory and Disaster Prevention Research Institute, independently or co-operatively. Continuous observation at Shinko has been carried out to investigate the time variation of the seismic activity since the joint observation of ultramicro-earthquakes at the end of 1965. As the seismicity became active, continuous observation was started at Sanada, too, on June, 1966, with the main purpose of investigating the "Ishimoto-lida's relation" and the time variation of seismic activity, but it was abandoned on September, 1966 be-cause of overlapping the station with that of the Earthquake Research Institute. For studying the attenuation of seismic wave in short hypocentral distance and formulating the equation for calculating the magnitude of an earthquake, the Matsushiro swarm earth-quakes are a very good source observations. On the basis of this idea, we picked out four observation points on the array line from Matsushiro to Komoro, and installed com-pletely equipped low magnification seismographs of displacement type. The observation