TY - JOUR
T1 - Focal mechanisms and the stress field in the aftershock area of the 2018 Hokkaido Eastern Iburi earthquake (M JMA = 6.7)
AU - the Group for the Aftershock Observations of the 2018 Hokkaido Eastern Iburi Earthquake
AU - Susukida, Yuki
AU - Katsumata, Kei
AU - Ichiyanagi, Masayoshi
AU - Ohzono, Mako
AU - Aoyama, Hiroshi
AU - Tanaka, Ryo
AU - Takada, Masamitsu
AU - Yamaguchi, Teruhiro
AU - Okada, Kazumi
AU - Takahashi, Hiroaki
AU - Sakai, Shin’ichi
AU - Matsumoto, Satoshi
AU - Okada, Tomomi
AU - Matsuzawa, Toru
AU - Miyamachi, Hiroki
AU - Hirano, Shuichiro
AU - Yamanaka, Yoshiko
AU - Horikawa, Shinichiro
AU - Kosuga, Masahiro
AU - Katao, Hiroshi
AU - Iio, Yoshihisa
AU - Nagaoka, Airi
AU - Tsumura, Noriko
AU - Ueno, Tomotake
AU - Susukida, Yuki
AU - Katsumata, Kei
AU - Ichiyanagi, Masayoshi
AU - Ohzono, Mako
AU - Aoyama, Hiroshi
AU - Tanaka, Ryo
AU - Takada, Masamitsu
AU - Yamaguchi, Teruhiro
AU - Okada, Kazumi
AU - Takahashi, Hiroaki
AU - Sakai, Shin’ichi
AU - Miyakawa, Koji
AU - Tanaka, Shin’ichi
AU - Ando, Miwako
AU - Okada, Tomomi
AU - Matsuzawa, Toru
AU - Uchida, Naoki
AU - Azuma, Ryosuke
AU - Takagi, Ryota
AU - Yoshida, Keisuke
AU - Nakayama, Takashi
AU - Hirahara, Satoshi
AU - Terakawa, Toshiko
AU - Yamanaka, Yoshiko
AU - Maeda, Yuta
AU - Horikawa, Shinichiro
N1 - Funding Information:
We thank Takuya Nishimura, Andrew Michael, and an anonymous reviewer for valuable comments. We thank Toshiko Terakawa for valuable discussions. We used waveform data from seismic stations maintained by JMA, and we also used waveform data from High-Sensitivity Seismograph Network of Japan (Hi-net) maintained by NIED. We used observation equipment at some seismic stations supported by the Earthquake Research Institute Joint Usage/Research Program 2016-F2-02, 2017-F2-02, 2018-F2-02, 2019-F2-02, and 2020F2-02. GMT-SYSTEM (Wessel and Smith 1991) was used for mapping data. A list of individual members of the Group for the Aftershock Observations of the 2018 Hokkaido Eastern Iburi Earthquake follows: Yuki Susukida1,11, Kei Katsumata1, Masayoshi Ichiyanagi1, Mako Ohzono1, Hiroshi Aoyama1, Ryo Tanaka1, Masamitsu Takada1, Teruhiro Yamaguchi1, Kazumi Okada1, Hiroaki Takahashi1, Shin’ichi Sakai2, Koji Miyakawa2, Shin’ichi Tanaka2, Miwako Ando2, Satoshi Matsumoto3, Tomomi Okada4, Toru Matsuzawa4, Naoki Uchida4, Ryosuke Azuma4, Ryota Takagi4, Keisuke Yoshida4, Takashi Nakayama4, Satoshi Hirahara4, Toshiko Terakawa5, Yoshiko Yamanaka5, Yuta Maeda5, Shinichiro Horikawa5, Hiroki Miyamachi6, Shuichiro Hirano6, Hiroshi Yakiwara6, Masahiro Kosuga7, Takuto Maeda7, Hiroshi Katao8, Yoshihisa Iio8, Airi Nagaoka8, Noriko Tsumura9, Masahiro Shimazaki9, Tomotake Ueno10, and Youichi Asano10, where1 Hokkaido University, 2 University of Tokyo,3Kyushu University,4Tohoku University,5Nagoya University,6Kagoshima University,7Hirosaki University,8Kyoto University,9Chiba University,10National Research Institute for Earth Science and Disaster Resilience and 11KOZO KEIKAKU ENGINEERING Inc., Tokyo, Japan.
Funding Information:
This study was partly supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its “The Second Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research)”. This study was also partly supported by MEXT KAKENHI grant 18K19952.
Publisher Copyright:
© 2020, The Author(s).
PY - 2021/12
Y1 - 2021/12
N2 - 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.[Figure not available: see fulltext.]
AB - 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.[Figure not available: see fulltext.]
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U2 - 10.1186/s40623-020-01323-x
DO - 10.1186/s40623-020-01323-x
M3 - Article
AN - SCOPUS:85107360889
SN - 1343-8832
VL - 73
JO - earth, planets and space
JF - earth, planets and space
IS - 1
M1 - 1
ER -