The 2018 Hokkaido Eastern Iburi earthquake (MJMA = 6.7) was triggered by a strike-slip faulting in a stepover segment: insights from the aftershock distribution and the focal mechanism solution of the main shock

Earth, Planets and Space

Masahiro Kosuga¹  Shinichiro Horikawa²  Toshiko Terakawa²  Shuichiro Hirano³  Shin’ichi Sakai⁴  Teruhiro Yamaguchi⁵  Kazumi Okada⁵  Hiroshi Aoyama⁵  Mako Ohzono⁵  Kei Katsumata⁵  Hiroaki Takahashi⁵  Masamitsu Takada⁵  Masayoshi Ichiyanagi⁵  Ryo Tanaka⁵  Satoshi Matsumoto⁶  Tomomi Okada⁷  Toru Matsuzawa⁷  Noriko Tsumura⁸  Hiroshi Katao⁹  Airi Nagaoka⁹  Yoshihisa Iio⁹  Tomotake Ueno^1,10 

[1]0000 0001 0673 6172, grid.257016.7, Earthquake and Volcano Observatory, Hirosaki University, Hirosaki, Japan

[2]0000 0001 0943 978X, grid.27476.30, Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan

[3]0000 0001 1167 1801, grid.258333.c, Nansei-Toko Observatory for Earthquakes and Volcanoes, Graduate School of Science and Engineering, Kagoshima University, Kagoshima, Japan

[4]0000 0001 2151 536X, grid.26999.3d, Earthquake Research Institute, University of Tokyo, Tokyo, Japan

[5]0000 0001 2173 7691, grid.39158.36, Faculty of Science, Institute of Seismology and Volcanology, Hokkaido University, Sapporo, Japan

[6]0000 0001 2242 4849, grid.177174.3, Institute of Seismology and Volcanology, Kyushu University, Fukuoka, Japan

[7]0000 0001 2248 6943, grid.69566.3a, Research Center for Prediction of Earthquakes and Volcanic Eruptions, Tohoku University, Sendai, Japan

[8]0000 0004 0370 1101, grid.136304.3, Department of Earth Science, Faculty of Science, Chiba University, Chiba, Japan

[9]0000 0004 0372 2033, grid.258799.8, Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan

[10]National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan

关键词: The Hokkaido Eastern Iburi earthquake;    Strike-slip fault;    Reverse fault;    Aftershock distribution;    Focal mechanism solution;    Local seismic network;    Stepover segment;   

DOI  :  10.1186/s40623-019-1032-8

来源: publisher

【 摘 要 】

The Hokkaido Eastern Iburi earthquake (MJMA = 6.7) occurred on September 6, 2018, in the Hokkaido corner region where the Kurile and northeastern Japan island arcs meet. We relocated aftershocks of this intraplate earthquake immediately after the main shock by using data from a permanent local seismic network and found that aftershock depths were concentrated from 20 to 40 km, which is extraordinarily deep compared with other shallow intraplate earthquakes in the inland area of Honshu and Kyushu, Japan. Further, we found that the aftershock area consists of three segments. The first segment is located in the northern part of the aftershock area, the second segment lies in the southern part, and the third segment forms a stepover between the other two segments. The hypocenter of the main shock, from which the rupture initiated, is located on the stepover segment. The centroid moment tensor solution for the main shock indicates a reverse faulting, whereas the focal mechanism solution determined by using the first-motion polarity of the P wave indicates strike-slip faulting. To explain this discrepancy qualitatively, we present a model in which the rupture started as a small strike-slip fault in the stepover segment of the aftershock area, followed by two large reverse faulting ruptures in the northern and southern segments.

【 授权许可】

CC BY