The Time Variation of the Focal Mechanism and the Activity of Earthquake S warms

Abstract

The earthquake swarms which have occurred in Japan since 1962 have been investigated. Their origins are found to be situated in the volcanic region, which coincides with the results investigated by Mogi. The swarms are generally separated into three stages. Each of the three stages corresponds to the foreshocks, main shock and maximum aftershock respectively in the sequence of normal shallow earthquakes of the foreshock type. The pressure directions of the shocks change with time corresponding to the time variation of the activity of the swarm.