琵琶湖周辺における極浅発地震の発震機構

抄録

Focal mechanisms of very shallow earthquakes on the west and the southwest of Lake Biwa have been determined by smoothing the first-motion radiation pattern and by individual solutions. Published focal mechanism solutions are also used to examine the tectonic stress which generates earthquakes in the north Kinki district. Along the west coast and the east coast of Lake Biwa seismic active regions of very shallow earthquakes occur and in Lake Biwa seismic activity is very low. Most of mechanism solutions in these active regions are reverse faultings with the maximum pressure axes in the direction of nearly east-west or southeast-northwest. In other regions of north Kinki district and west Chubu district dominant type of faulting is strike-slip with the same pressure direction. These types of faulting from earthquake focal mechanism solutions agree well with those of tectonic active faults developed in this area. The reverse faulting as well as the high seismicity on the both coasts of Lake Biwa is consistent with the subsedence of Lake Biwa which has been continued throuth the Quaternary.