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タイトル: Earthquake Mechanisms Associated with the Conjunction of the Sinking Plates beneath the Kanto District, Central Japan
その他のタイトル: 関東地方の地震メカニズム
著者: Maki, Tadashi
Kawasaki, Ichiro
Horie, Akiko
著者(別言語): 牧, 正
川崎, 一朗
堀江, 晶子
発行日: 1981年3月7日
出版者: 東京大学地震研究所
掲載誌情報: 東京大学地震研究所彙報. 第55冊第3号, 1981.3.7, pp. 577-600
抄録: A study of the focal mechanisms was made for 49 subcrustal earthquakes which occurred in the seismically active regions of the Kanto District, by using the dada on P wave first motion. These data were collected from the observational stations of the Earthguake Research Institute (ERI) and from the seismological bulletins of the Japan Meteorological Agenay (JMA) and the International Seismological Centre (ISC). Shallower earthquakes located at a depth of about 45 km below the western end of Ibaraki Prefecture had the focal mechanism of underthrusting at a low dip angle towards the northwest. The spatial distribution of the hypocenters in this region, showing a linear alignment of the epicenters and a gentle dipping to the northwest, is consistent with the pole on the nodal plane dipping to the northwest. These earthquakes are interpreted as being caused by underthrusting towards the northwest along the upper boun- dary of the Pacific Plate. Deeper earthquakes, located in the eastern side of the 140°E line, extending from the western part of Chiba Prefecture to the southwestern part of Ibaraki Prefecture, having a focal d pth around 70 km within the downgoing Pacific Plate, show the focal mechanism of the vertical dip-slip with the western side descending. These earthquakes take place in the colliding region of the minor seismic zone sinking to the east and the Pacific Plate sinking to the west. The earthquakes in this region are interpreted as being caused by the subcrustal collision of the Philippine Sea Plate with the Pacific Plate.
URI: http://hdl.handle.net/2261/12767
ISSN: 00408972


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