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タイトル: Electric Field Variations Related to Seismic Swarms
その他のタイトル: 群発地震に伴う電解変動
著者: Fujinawa, Yukio
Takahashi, Kozo
Matsumoto, Takumi
Iitaka, Hiroshi
Doi, Takuya
Nakayama, Takeshi
Sawada, Toyoaki
Sakai, Hideo
著者(別言語): 藤縄, 幸雄
高橋, 耕三
松本, 巧己
飯高, 弘
土井, 卓也
中山, 武
澤田, 豊明
酒井, 英男
キーワード: groundwater motion
electric field
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. 391-415
抄録: We have been observing subsurface electric field variations using specially designed antenna with a long casing pipe in borehole (Ultra-Long-Electrode Measurement : ULEM) at 12 sites in the central part of Japan since 1989. Analyses of electromagnetic field variation data around the times of several seismic activities, particularly during seismic swarms, indicate that the electric field anomalies correlate well with crustal activity around the site. Field changes appeared in the DC, ULF, and ELF/VLF bands ; the ELF/VLF bands did not always correlate with other bands, but were limited to the most active period. Electric signals associated with a seismic swarm are detected locally within 100 km from the network. Detectability is very heterogeneous, and selectivity of signal detection is largely attributed to the degree of hydraulic connectivity between the source generation zone and the site. The anomalies could be observed more clearly using the borehole antenna than by sensors on the ground surface, probably because of the shorter distance to the source zone, as well as the large length for the sensors to respond to field variations in the heterogeneous media. The field change anomalies may be caused by electric-kinetic effects induced by variations of the confined water circulation regime in association with earthquake occurrence. It is probable that pore water pressure changes preceding and during earthquakes can be detected by an electromagnetic field sensor embedded in the deep borehole near the path of water circulation around faults.
URI: http://hdl.handle.net/2261/13232
ISSN: 00408972


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