SOURCE CHARACTERISTICS OF THE 1983 NIHONKAI-CHUBU (JAPAN SEA) EARTHQUAKE AND SEISMIC ACTIVITY IN NORTHERN TOHOKU PRECEDING TO THE EARTHQUAKE

概要

論文の詳細を見る
We studied the source characteristics of the 1983 Nihonkai-chubu (Japan Sea) earthquake (M_<JMA> 7.7) and seismic activity preceding to the earthquake in and around the source area. A double envelope pattern on strong motion accelerograms showed that the Nihonkai-chubu earthquake consisted of two major events, emitting large amounts of high-frequency energy in two stages. Relative locations of the two events were determined from time differences between the first S-arrivals of the two events identified on the accelerograms from 10 stations. The second event was located about 44 km NNE of the first event which originated at the southern end of the aftershock area. The relative locations, combined with the aftershock distribution, suggested that the source area of the first event was the southern part of the aftershock area and the second event the central part. The two source area are separated by a zone of low aftershock activity west of Kyuroku Island. This zone is considered as a barrier which stopped the first event for about 10 sec. Relocation of the aftershocks of the 1983 Nihonkai-chubu earthquake and of the 1964 Off-Oga earthquake (M_<JMA> 6.9) showed that the source area of the Off-Oga earthquake completely overlapped the source area of the first event of the 1983 earthquake. The Off-Oga earthquake probably terminated at the barrier zone west of Kyuroku Island and failed to become as large as the 1983 earthquake. A smaller amount of average slip over the source area is a possible reason for the termination at the barrier zone. Several earthquake-swarm activities in northern Tohoku during 1972-1982 probably were caused by an increase in regional tectonic stress associated with the generation of the 1983 Nihonkai-chubu earthquake. In particular, the 1978 Iwasaki earthquake-swarm can be recognized as premonitory seismic activity because it occurred near the source area of the 1983 earthquake in a place where earthquake-swarm activities had been very rare, and because it occurred simultaneously with a conspicuous uplift of the Oga Peninsula which is also situated near the source area of the 1983 earthquake. Close examination of historical records showed that the 1694 Genroku earthquake and the successive large earthquakes of the 18th century along the coast of the Japan Sea had also been preceded by an earthquake-swarm that originated at a place near the source area of the 1978 Iwasaki earthquake-swarm. Earthquake-swarms along the coast of the Japan Sea must be given adequate attention because they may represent premonitory seismic activity prior to large earthquakes in the northern part of the Japan Sea.
日本自然災害学会の論文

SOURCE CHARACTERISTICS OF THE 1983 NIHONKAI-CHUBU (JAPAN SEA) EARTHQUAKE AND SEISMIC ACTIVITY IN NORTHERN TOHOKU PRECEDING TO THE EARTHQUAKE

スポンサーリンク

概要

著者

関連論文

スポンサーリンク