[J05-1] Crustal dynamics: Multidisciplinary approach to seismogenesis I

[J05-1-03] Stress field around fault zones of the 2016 Kumamoto earthquake sequence (Mj7.3)
inferred from moment tensor data from 1996 to 2016

^○Satoshi Matsumoto¹, Yusuke Yamashita², Manami Nakamoto³, Masahiro Miyazaki², Shin-ichi Sakai⁴, Yoshihisa Iio², Kazuhiko Goto⁵, Tomomi Okada⁶, Mako Ohzono⁷, Toshiko Terakawa⁸, Masahiro Kosuga⁹, Masayuki Yoshimi¹⁰, Youichi Asano¹¹ (1.Kyushu University, Shimabara, Japan, 2.Kyoto University, Uji, Japan, 3.National, Institute of Polar Research, Tokyo, Japan, 4.University of Tokyo, Tokyo, Japan, 5.Kagoshima University, Kagoshima, Japan, 6.Tohoku University, Sendai, Japan, 7.Hokkaido University, Sapporo, Japan, 8.Nagoya University, Nagoya, Japan, 9.Hirosaki University, Hirosaki, Japan, 10.National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan, 11. National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan)

The 2016 Kumamoto earthquake sequence started from 14 April 2016 in Kumamoto prefecture, middle part of Kyushu Island, Japan and involved the largest event with magnitude of 7.3 occurred on 16 April 2016. Events over M 6 also occurred before and after the mainshock. High background seismic activity observed in this area before the earthquake occurrence. Inelastic strain distribution in the area estimated by seismic moment tensor data implies that the major events of the sequence occurred “around" large strain region. This suggests that the large inelastic strain created stress concentration. In this study we analyzed the seismic moment tensor data before and after the occurrence of the sequence and estimated stress field in the hypocentral area. As general tendency, dominated minimum principal stress (sigma 3) in the N-S direction obtained and the maximum principal stress takes value close to the moderate one. The stress field reveals spatial heterogeneous feature, which varies from southern to northern part of the area. We found that the stress field around the fault zone is consistent with co-seismic fault behavior of the earthquake sequence and decreasing maximum horizontal stress. The results shows that complex co-seismic rupture and the seismic activity associated with the sequence could be attributed to the uniaxial extension of deviatoric stress field.