中央アリューシャンADAK地震観測網と地震予知・テクトニクスの研究

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書誌事項

タイトル別名
  • Summary of Earthquake Prediction and Seismotectonic Research in the Central Aleutian Island Arc Using Data from Adak, Alaska Seismograph Network
  • チュウオウ アリューシャン ADAK ジシン カンソクモウ ト ジシン ヨチ

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抄録

The Adak seismograph network has located 8123 local earthquakes in the central Aleutian island are between August, 1974 and October, 1982. The seismically most active area monitored by the Adak network is the main thrust zone at a depth of 15km to 50km. This zone is characterized by thrust focal mechanisms with the greatest principal stress axis parallel to the relative motion of the Pacific and North American plates. In the Adak Canyon region, there is a zone of east-west extensional normal faulting overlying the thrust zone. Oblique subduction of the Pacific plate may be responsible for this normal faulting as well as for the series of submarine canyons west of Adak Canyon. Between 50km and 100km a narrow band of hypocenters dipping at 45° defines the Benioff zone. At 100km there is an apparent bend in the Benioff zone, and earthquakes extend to 275km at an apparent angle of 65°. Analysis of data from networks of ocean bottom seismographs deployed south of the island arc in 1978 and 1979 suggests that the shallow earthquakes in the main thrust zone have a wider depth range than determined from the land-based network alone and that the apparent bend in the Benioff zone is produced by lateral heterogeneity in the mantle caused by the subducting slab and does not exist. The distribution of hypocenters and focal mechanisms of deep earthquakes is consistent with a subducted slab which is warped at depth. Analysis of the seismccty preceding all the earthquakes with mb≥4.5 suggests that detectable foreshocks precede less than 10% of these larger events. Investigations of the focal mechanism of small earthquakes preceding three larger earthquakes in the main thrust zone indicate a possible change of mechanism in the period 1-10 month prior to the larger events.

収録刊行物

  • 地震　第２輯

    地震　第２輯 37 (2), 247-256, 1984

    公益社団法人 日本地震学会

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