Earthquake Swarm Activity in the Northern Tokyo Bya

概要

論文の詳細を見る
An earthquake swarm sequence occurring in the northern Tokyo Bay during the period from July 11 to August 3, 1979, was studied on the basis of the waveform analysis. The sequence was monitored by the magnetic-tape recording system consisting of six stations distributed around the swarm area. The seismograms obtained at each station exhibit similar waveforms belonging to an earthquake family. The precise epicenters of the 16 earthquakes determined, using the detailed differences of S-P times, show a very small focal region of about 400 meters in dimension, including four groups where the locations between the events are separated by, at most, few ten meters. Within the focal regions, a SE-NW trend was observed with events apparently migrating up and then back down. The source spectra obtained from S waves at two stations show identical forms having similar corner frequency, and the linear dimension estimated from the corner frequency is constant with a value of about 200 meters for the earthquakes with magnitudes of 1.8 to 3.0. Considering the epicentral area and the source dimension, it is expected that the earthquake swarm occurred over the same fault as a repeated slipping, especially the events locate within few ten meters occurred as the earthquakes of a stick-slip type.1979年7月11日より8月3日にかけ,東京湾北部で発生した群発地震について,地震波の波形解析を行ない,その活動様式についていくつかの特徴ある結果を得た.主な結果は次の通りである.(1)合計34個の震源決定された地震のうち,M≧1.8の地震16個の波形について調べた結果,1978年の伊豆半島北部で発生した群発地震と同様に,今回の地震も例外なく相似地震によって構成されていることが解った.(2)早送り記録(50mm/sec)の重ね合わせから得たS-P時間の違いから震源を決めた結果,夫々の地震は略400mの範囲内に分布し,更に時間の経過と共に,SE-NW方向への移動がみられた.(3)S波についてのスペクトル解折から求めたCorner frequencyはM=1.8-3.0の間で略一定であり,Corner frequencyから求めた震源の大きさは約200mの値を示す.震源分布,及びそれらの地震の震源の大きさを考慮すると,これらの地震はおそらく同じ断層面上で繰返し発生し,特に約50mの範囲内に分布する4組の地震群は同じ断層面上でStick-slip型の地震として発生したものと推定される.
1981-03-07

Earthquake Swarm Activity in the Northern Tokyo Bya

スポンサーリンク

概要

論文 | ランダム

スポンサーリンク