著者

山科 健一郎 高橋 正義

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.58, no.3, pp.655-666, 1984-01-14

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1982年5月に伊豆半島北東部の川奈崎付近で起きた群発地震活動(M=2.0)について,現地で臨時観測を行った.観測期間は活動の最盛期を過ぎた5月12~14日で,2観測点は固定し,他の1観測点を次々に移動する方式をとった.川奈崎付近に集中して発生した一群の地震(ここではa型と呼ぶ)があり,計5ケ所のP時刻から平均的な震源の位置と観測点補正を求めた.今回のような移動多点観測も,ある場合には役に立つものと思われる.一方,川奈崎付近の活動は5月13日の朝に急速に低下したが,ちょうどその前に,約30km南方で群発活動が起きている.活動の低下はまずa型の地震群に現われ,数時間遅れて周辺も静かになった.A tail of the swarm activity (M=2.0) near Kawana-zaki in the northeastern part of the Izu Peninsula in May, 1982, was observed by a temporary microseismic network installed close to the epicentral region. During the observations on May 12-14th, two seismometers were fixed at the respective places and another was moved from place to place. Station corrections and the average location of the events which occurred within a small area near Kawana-zaki (they are called "a-type" in this paper) were obtained from P arrivals of the two fixed and three tentative stations, suggesting the utility of the moving installation of instruments in some cases. The observation also shows a distinct decrease in activity near Kawana-zaki in the morning of May 13th, following the earthquake swarm which occurred about 30km to the south. The decrease in activity occurred at fast in the hypocentral region of the a-type events, and in the adjacent areas several hours later.