特集　火山活動と地殻応力場　ダイクの貫入と群発地震

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書誌事項

タイトル別名
  • Volcanism and Crustal Stress Field. Dyke Intrusion and Earthquake Swarms.
  • ダイク ノ カンニュウ ト グンパツ ジシン

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抄録

A kinematic mechanism of earthquake swarms induced by dyke intrusions was investigated for the seismo-volcanic activity off the east coast of the Izu Peninsula in July 1989. In this activity an intensive earthquake swarm composed of tectonic earthquakes continued for one week with large crustal deformation. From the crustal deformation data Okada and Yamamoto revealed that a dyke with 3 km width intruded from 7 to 1 km depth in the first day of the intensive swarm and then thickned to be 1 to 1.5 m thick. Relocated hypocenters show that the seismically active region moved from deep to shallow during the priod of the ascent of the dyke, suggesting the earthquakes occurred around the top of the intruded dyke. On the basis of the seismic data and the Okada and Yamamoto's dyke model, we examined three possible explanations or the cause of dyke-induced-earthquake swarm, that is, the stress change due to dyke intrusion, open crack-shear crack interaction (Hill's model) and the effect of pore-fluid-pressure increase, In order to explain the focal depth migration, the stress change due to dyke intrusion is the most favorable cause of the earthquake swarm, because the dyke intrusion increases differential stress above the top of the dyke and decreases that below the top. The observed focal mechanism type is consistent with the one expected from the ambient tectonic stress and the stress change due to the dyke intrusion.

収録刊行物

  • 地学雑誌

    地学雑誌 103 (5), 537-547, 1994

    公益社団法人 東京地学協会

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