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タイトル: Seismological Evidence for the Influence of Fluids and Magma on Earthquakes
その他のタイトル: 流体とマグマの地震発生への影響 : 地震学的考察
著者: Zhao, Dapeng
Mishra, Om P.
Sanda, Ryohei
Obara, Kazushige
Umino, Norihito
Hasegawa, Akira
著者(別言語): 趙, 大鵬
三田, 亮平
小原, 一成
海野, 徳仁
長谷川, 昭
キーワード: fluids
seismic tomography
slab dehydration
発行日: 2002年2月12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76冊第3号, 2002.2.12, pp. 271-289
抄録: In this paper we present seismological evidence for the influences of fluids and arc magma on the generation of large earthquakes in the crust and the subducting oceanic slabs under the Japan Islands. The relationship between seismic tomography and large crustal earthquakes (M 5.7-8.0) in Japan during the period of 116 years from 1885 to 2000 is investigated, and it is found that most of the large crustal earthquakes occurred in or around zones of low seismic velocity. The low-velocity zones may represent weak sections of the seismogenic crust. Crustal weakening is closely related to the subduction process in this region. Along the volcanic front and in back-arc areas, crustal weakening may be caused by active volcanoes and arc magma, resulting from the convective circulation process in the mantle wedge and dehydration reactions in the subducting slab. Recent examples are the 1984 West Nagano earthquake (M 6.8) and the 2000 West Tottori earthquake (M 6.9), both occurred adjacent to volcanoes. In the forearc region of southwest Japan, fluids are detected in the 1995 Kobe earthquake source zone, which may have contributed to the rupture nucleation. The fluids may originate from the dehydration of the subducting Philippine Sea slab. The recent 2001 Geiyo earthquake (M6.4) occurred at 50 km depth within the subducting Philippine Sea slab, and it may also be related to the slab dehydration process. A detailed 3-D velocity structure is determined for the northeast Japan forearc region using data from 598 earthquakes that occurred under the Pacific Ocean with hypocenters well located with sP depth phases. The results show that strong lateral heterogeneities exist along the slab boundary, which may represent asperities and results of slab dehydration, and may affect the degree and the extent of interplate seismic coupling. These results indicate that large earthquakes do not strike anywhere, but only in anomalous areas that may be detected with geophysical methods. The generation of a large earthquake is not a pure mechanical process, but is closely related to the physical and chemical properties of materials in the crust and upper mantle, such as magma and fluids.
URI: http://hdl.handle.net/2261/13222
ISSN: 00408972


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