北陸地方の微小地震活動の特徴について (その2)

Abstract

Almost 7 years have passed since the Telemeter Obsevation System was set up at theHokuriku Microearthquake observatory. The number of earthquakes observed by the systemamounted to 7978 from the beginning of May 1976 to the end of December 1982. Monthlynumbers of events were counted for 10 regions in the Hokuriku and Northern KinkiDistricts. In 1978, the activities rose up to a peak in the earstern regions, namely, nearAzai Satellite station, around Shirotori and Gujohachima, near Takayama, and Ohtaki withits vicinity. In the western regions, that is, near Mihama satellite station and westward areas, however, the activity was very low in that year. This fact suggests that a discontinuity ofstress field lies between the two groups of regions.Earthquake swarms near Mt. Akausagi, at the border of the Fukui and Ishikawa Pre-fectures, are also studied. This area was a seismic gap before the swarm occurred in June1980. In December 1982 another swarm of a smaller number of events and of a shorter timeduration occurred about 2 km west of the first one. These two swarms may show anexpansion of an active seismic zone.