京都周辺に発生する微小地震(2)

Abstract

One of the conclusions drawn in the first paper that micro-earthquakes are very frequent in abelt.like region running from the west coast of Lake Biwa to Osaka Bay is strongly confirmed.The focal depths are shallow in the east side of the belt.like region, and become deeper towardthe west end. The deepest focal depths lie in the crust. The distribution of the first motions of Pwaves is of quadrant type, and the horizontal component of the maximum pressure lies in the E.Wdirection, which agrees comparatively well with the direction of the maximum pressure of veryshallow earthquakes in Kinki District. The frequent occurrence of micro-earthquakes and the largerearthr1uakes in the belt.like region might have some relations to geologically distinctive featuressuch as the abnormal variation of Bouguer anomaly, the minimum horizontal displacements andthe existence of Quaternary active faults found in the region concerned.