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Focal mechanisms and the stress field in the aftershock area of the 2018 Hokkaido Eastern Iburi earthquake (M-JMA=6.7)

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Title: Focal mechanisms and the stress field in the aftershock area of the 2018 Hokkaido Eastern Iburi earthquake (M-JMA=6.7)
Authors: Susukida, Yuki Browse this author
Katsumata, Kei Browse this author →KAKEN DB
Ichiyanagi, Masayoshi Browse this author
Ohzono, Mako Browse this author
Aoyama, Hiroshi Browse this author
Tanaka, Ryo Browse this author
Takada, Masamitsu Browse this author
Yamaguchi, Teruhiro Browse this author
Okada, Kazumi Browse this author
Takahashi, Hiroaki Browse this author
Sakai, Shin'ichi Browse this author
Matsumoto, Satoshi Browse this author
Okada, Tomomi Browse this author
Matsuzawa, Toru Browse this author
Miyamachi, Hiroki Browse this author
Hirano, Shuichiro Browse this author
Yamanaka, Yoshiko Browse this author
Horikawa, Shinichiro Browse this author
Kosuga, Masahiro Browse this author
Katao, Hiroshi Browse this author
Iio, Yoshihisa Browse this author
Nagaoka, Airi Browse this author
Tsumura, Noriko Browse this author
Ueno, Tomotake Browse this author
Miyakawa, Koji Browse this author
Tanaka, Shin'ichi Browse this author
Ando, Miwako Browse this author
Uchida, Naoki Browse this author
Azuma, Ryosuke Browse this author
Takagi, Ryota Browse this author
Yoshida, Keisuke Browse this author
Nakayama, Takashi Browse this author
Hirahara, Satoshi Browse this author
Terakawa, Toshiko Browse this author
Maeda, Yuta Browse this author
Miyamachi, Hiroki Browse this author
Yakiwara, Hiroshi Browse this author
Keywords: The Hokkaido Eastern Iburi earthquake
Reverse fault
Aftershock distribution
Focal mechanism solution
Temporary seismic network
Stress inversion
Issue Date: 1-Dec-2021
Publisher: Springer
Journal Title: Earth planets and space
Volume: 73
Issue: 1
Start Page: 1
Publisher DOI: 10.1186/s40623-020-01323-x
Abstract: The tectonic stress field was investigated in and around the aftershock area of the Hokkaido Eastern Iburi earthquake (M-JMA = 6.7) occurred on 6 September 2018. We deployed 26 temporary seismic stations in the aftershock area for approximately 2 months and located 1785 aftershocks precisely. Among these aftershocks, 894 focal mechanism solutions were determined using the first-motion polarity of P wave from the temporary observation and the permanent seismic networks of Hokkaido University, Japan Meteorological Agency (JMA), and High Sensitivity Seismograph Network Japan (Hi-net). We found that (1) the reverse faulting and the strike-slip faulting are dominant in the aftershock area, (2) the average trend of P- and T-axes is 78 degrees +/- 33 degrees and 352 degrees +/- 51 degrees, respectively, and (3) the average plunge of P- and T-axes is 25 degrees +/- 16 degrees and 44 degrees +/- 20 degrees, respectively: the P-axis is close to be horizontal and the T-axis is more vertical than the average of the P-axes. We applied a stress inversion method to the focal mechanism solutions to estimate a stress field in the aftershock area. As a result, we found that the reverse fault type stress field is dominant in the aftershock area. An axis of the maximum principal stress (sigma(1)) has the trend of 72 degrees +/- 7 degrees and the dipping eastward of 19 degrees +/- 4 degrees and an axis of the intermediate principal stress (sigma(2)) has the trend of 131 degrees +/- 73 degrees and the dipping southward of 10 degrees +/- 9 degrees, indicating that both of sigma(1)- and sigma(2)-axes are close to be horizontal. An axis of the minimum principal stress (sigma(3)) has the dipping westward of 67 degrees +/- 6 degrees that is close to be vertical. The results strongly suggest that the reverse-fault-type stress field is predominant as an average over the aftershock area which is in the western boundary of the Hidaka Collision Zone. The average of the stress ratio R = (sigma(1) - sigma(2))/(sigma(1) - sigma(3)) is 0.61 +/- 0.13 in the whole aftershock area. Although not statistically significant, we suggest that R decreases systematically as the depth is getting deep, which is modeled by a quadratic polynomial of depth.
Type: article
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

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