Departmental Bulletin Paper 2012年に発生した北海道北部中川町付近の群発地震活動
The 2012 Earthquake Swarm in Nakagawa town, northern Hokkaido

一柳, 昌義  ,  高橋, 浩晃  ,  山口, 照寛  ,  東, 龍介  ,  山田, 卓司  ,  大園, 真子  ,  眞城, 亮成  ,  笠原, 稔  ,  谷岡, 勇市郎

78pp.37 - 51 , 2015-03-19 , 北海道大学大学院理学研究院
An earthquake swarm begun at 15 July 2012 in Nakagawa town of northern Hokkaido. The largest earthquake with MJMA4.3 occurred on 16 July 2012. We carried out temporal seismic observation with seven stations from 18 July 2012 to the last October 2012. Hypocenters were calculated using the Double-Difference hypocenter determination procedure with a local one dimensional P-wave velocity structure. Precise hypocenter data indicated that epicenters were distributed in very narrow area of 2 km×2 km with shallow depth from 4 km to 7 km. Earthquakes after middle of August occurred only in southern part of the region and depth had got shallower with time. Hypocenters indicated no clear alignment in consistent with any nodal planes of major earthquakes. An independent hypocenter cluster with shallower than 2 km was observed above the main activity area. A slow slip event (SSE) with Mw 5.4 coincidentally detected by GNSS crustal deformation data during the swarm. This swarm was situated at the southeastern end of the fault of SSE. This fact suggested that seismic swarm might triggered SSE or was induced by SSE.

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