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北海道大学地球物理学研究報告 = Geophysical bulletin of Hokkaido University >
第70号 >

2004 年留萌支庁南部地震震源域の重力測定

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Title: 2004 年留萌支庁南部地震震源域の重力測定
Other Titles: Gravity survey in and around the focal area of 2004 Rumoi-nanbu earthquake, Northern Hokkaido, Northern Japan
Authors: 本多, 亮1 Browse this author
神山, 裕幸2 Browse this author
山口, 照寛3 Browse this author
市原, 寛4 Browse this author
茂木, 透5 Browse this author →KAKEN DB
Authors(alt): HONDA, Ryo1
KAMIYAMA, Hiroyuki2
YAMAGUCHI, Teruhiro3
ICHIHARA, Hiroshi4
MOGI, Toru5
Issue Date: 15-Mar-2007
Publisher: 北海道大学大学院理学研究院自然史科学部門(地球物理学)
Journal Title: 北海道大学地球物理学研究報告
Journal Title(alt): Geophysical bulletin of Hokkaido University
Volume: 70
Start Page: 27
End Page: 41
Abstract: An earthquake (MJMA 6.1), occurred in December 14, 2004, at southern area of Rumoi sub-prefecture, northern Hokkaido, Japan. The earthquake intensity was assumed to 6 in Obira town. In Hokkaido, this is the first inland earthquake larger than M6 since Teshikaga earthquake (MJMA 6.5, 1967). Detailed aftershock distribution shows that the aftershocks occur on an eastward dipping plane of 10 km square, depth of which 5 km. The mainshock assumed to have occurred near the southern end of this plane. Despite the sparseness of existing gravity stations over the focal region, it was found that the aftershocks occur just above the gravitational rise of about 20 mGals. So the gravity survey was operated in Nov. 2005 to Aug. 2006, to make a detailed Bouguer anomaly map and to explicate the subsurface structure of the focal region. The measurement was done with CG-3 type gravimeter. Measurement positions were carefully decided by operating differential GPS observation. The accuracy of altitude decision is within 1 meter in all of the measurement points. Besides, data provided by Japan Petroleum Exploration Co. Ltd. was very helpful. The appropriate assumed density was detected to 2300 kg/m3, using density log of deep borehole near the focal region, and the correlations of gravity correction terms. The Bouguer anomaly map by current dataset also shows good coincidence with aftershock distribution.
Type: bulletin (article)
Appears in Collections:北海道大学地球物理学研究報告 = Geophysical bulletin of Hokkaido University > 第70号

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