Abstract

The tectonic stress field was investigated in and around the aftershock area of the Hokkaido Eastern Iburi earthquake (MJMA = 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° ± 33° and 352° ± 51°, respectively, and (3) the average plunge of P- and T-axes is 25° ± 16° and 44° ± 20°, 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 (σ1) has the trend of 72° ± 7° and the dipping eastward of 19° ± 4° and an axis of the intermediate principal stress (σ2) has the trend of 131° ± 73° and the dipping southward of 10° ± 9°, indicating that both of σ1- and σ2-axes are close to be horizontal. An axis of the minimum principal stress (σ3) has the dipping westward of 67° ± 6° 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 = (σ1 − σ2)/(σ1 − σ3) 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.

Details

Title
Focal mechanisms and the stress field in the aftershock area of the 2018 Hokkaido Eastern Iburi earthquake (MJMA = 6.7)
Author
Susukida Yuki 1 ; Katsumata Kei 2   VIAFID ORCID Logo  ; Ichiyanagi Masayoshi 2 ; Ohzono Mako 2 ; Aoyama, Hiroshi 2 ; Tanaka, Ryo 2 ; Takada Masamitsu 2 ; Yamaguchi Teruhiro 2 ; Okada Kazumi 2 ; Takahashi, Hiroaki 2 ; Sakai Shin’ichi 3 ; Matsumoto, Satoshi 4 ; Okada Tomomi 5 ; Matsuzawa Toru 5 ; Miyamachi Hiroki 6 ; Hirano Shuichiro 7 ; Yamanaka Yoshiko 8 ; Horikawa Shinichiro 8 ; Kosuga Masahiro 9 ; Katao Hiroshi 10 ; Iio Yoshihisa 10 ; Nagaoka Airi 10 ; Tsumura Noriko 11 ; Ueno Tomotake 12 ; Miyakawa Koji; Tanaka Shin’ichi; Ando Miwako; Uchida Naoki; Azuma Ryosuke; Takagi Ryota; Yoshida Keisuke; Nakayama Takashi; Hirahara Satoshi; Terakawa Toshiko; Maeda Yuta; Yakiwara Hiroshi; Maeda Takuto; Shimazaki Masahiro; Asano Youichi

1  Hokkaido University, Faculty of Science, Institute of Seismology and Volcanology, Sapporo, Japan (GRID:grid.39158.36) (ISNI:0000 0001 2173 7691); Kozo Keikaku Engineering Inc., Tokyo, Japan (GRID:grid.39158.36) 
2  Hokkaido University, Faculty of Science, Institute of Seismology and Volcanology, Sapporo, Japan (GRID:grid.39158.36) (ISNI:0000 0001 2173 7691) 
3  University of Tokyo, Earthquake Research Institute, Tokyo, Japan (GRID:grid.26999.3d) (ISNI:0000 0001 2151 536X) 
4  Kyushu University, Institute of Seismology and Volcanology, Fukuoka, Japan (GRID:grid.177174.3) (ISNI:0000 0001 2242 4849) 
5  Tohoku University, Research Center for Prediction of Earthquakes and Volcanic Eruptions, Sendai, Japan (GRID:grid.69566.3a) (ISNI:0000 0001 2248 6943) 
6  Kagoshima University, Graduate School of Science and Engineering, Kagoshima, Japan (GRID:grid.258333.c) (ISNI:0000 0001 1167 1801) 
7  Kagoshima University, Nansei-Toko Observatory for Earthquakes and Volcanoes, Research and Education Center for Natural Hazards, Kagoshima, Japan (GRID:grid.258333.c) (ISNI:0000 0001 1167 1801) 
8  Nagoya University, Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya, Japan (GRID:grid.27476.30) (ISNI:0000 0001 0943 978X) 
9  Hirosaki University, Earthquake and Volcano Observatory, Hirosaki, Japan (GRID:grid.257016.7) (ISNI:0000 0001 0673 6172) 
10  Kyoto University, Disaster Prevention Research Institute, Kyoto, Japan (GRID:grid.258799.8) (ISNI:0000 0004 0372 2033) 
11  Chiba University, Department of Earth Science, Faculty of Science, Chiba, Japan (GRID:grid.136304.3) (ISNI:0000 0004 0370 1101) 
12  National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan (GRID:grid.136304.3) 
Publication year
2021
Publication date
Jan 2021
Publisher
Springer Nature B.V.
e-ISSN
18805981
Source type
Scholarly Journal
Language of publication
English
DOI
https://doi.org/10.1186/s40623-020-01323-x
ProQuest document ID
2480545897
Copyright
© The Author(s) 2020. This work is published under http://creativecommons.org/licenses/by/4.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.