飛騨地方北部及び富山湾・能登半島周辺の最近の地震活動

Abstract

Seismicity and focal mechanism of small to moderate-size earth-earthquakes that occurredduring the latest five years from 1985 to 1989 in the northern Hida, Toyama bay and Noto pen-insula regions are discussed in some detail.It has been observed that seismicity beneath the Hida mountain range becomes activatednear Mt. Norikura in its southern part since March, 1986 and near Mt. Eboshi in its northernpart since February, 1990, indicating some migrations or alternate temporal variations of highactivity and quiescence. The focal mechanisms of all moderate-size shocks located in the northernsection indicate strike-slip type with one of nodal planes parallel to the axis of the mountain range, while those in the southern section show thrust-type mechanisms.Moderate seismicity has been noticed in the midst of and around the Toyama bay, with twolineations parallel or across the Toyama trough. Almost all these shocks show thrust-type me-chanisms with the maximum compressive stress oriented in a WNW-ESE direction, which aresimilar to the mechanisms of moderate-size earthquakes along the eastern margin of the JapanSea.High seismicity has been constantly observed along the Atotsugawa fault particularly in itseastern and western sections in constrast to low activity in the central segment.