琵琶湖周辺の地震活動について (II)

Abstract

The change of the mode of the crustal movement in the vicinity along the west coast ofLake Biwa was reported in 1973 by Danbara using the results of leveling plane survey. Andhe suggested to carry out leveling plane survey again in near future.It is made sure by the survey in 1976 there is not large crustal movement around thisregion during 1971-1976.Meanwhile the investigation of seismicity revealed clearly that there is no micro-earthqukesin the area along the eastern coast of Lake Biwa where was a great deal of damage by the largeearthquake M 7.4 in 1819. The above area might be called a kind of blank area of earthquake.The precise studies of micro-earthquakes mechanism concluded some earthquakes are thrusttypes in mechanism of earthquakes around Lake Biwa. This result is expected from thegeological backgrounds which are active dip-slip type faults system, subsidence of LakeBiwa and up-heaval of mountains around the lake.The observation of velocity of seismic waves was took place along the large fault, Hanaorein the west-side of Mt. Hira in the western coast of Lake Biwa.