JpGU-AGU Joint Meeting 2017

Presentation information

[JJ] Poster

S (Solid Earth Sciences) » S-SS Seismology

[S-SS17] [JJ] Fault Rheology and Earthquake Physics

Sun. May 21, 2017 1:45 PM - 3:15 PM Poster Hall (International Exhibition Hall HALL7)

convener:Takanori Matsuzawa(National Research Institute for Earth Science and Disaster Resilience), Takeshi Iinuma(National Research and Development Agency Japan Agency for Marine-Earth Science and Technology), Wataru Tanikawa(Japan Agency for Marine-Earth Science and Technology, Kochi Instutute for Core Sample Research), Hideki Mukoyoshi(Department of Geoscience Interdisciplinary Graduate School of Science and Engineering, Shimane University)

[SSS17-P08] Stress condition around M6.5 earthquake fault of the 2016 Kumamoto earthquake sequence

*Ayaho Mitsuoka1, Satoshi Matsumoto2, Yusuke Yamashita3, Manami Nakamoto4, Masahiro Miyazaki3, Shin'ichi Sakai5, Yoshihisa Iio3, Group for urgent joint seismic observation of the 2016 Kumamoto earthquake (1.Kyushu University, 2.Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, 3.Disaster Prevention Research Institute, Kyoto University, 4.National Institute of Polar Research, 5.Earthquake Research Institute, The University of Tokyo)

The 2016 Kumamoto earthquake sequence occurred at Hinagu and Futagawa fault zones under tectonic stress condition of strike slip or normal fault type. First large earthquake with magnitude 6.5 on April 14, 2016 was located at Hinagu fault zone with high seismic activity prior to the event. The stress condition around the fault zone is important to understand the generation of the earthquake. Especially, it is a key factor estimating the spatial variation of stress field at the depth of the hypocenter.
In this study, we estimated the deviatoric stress field and the stress ratio around Hinagu fault zone from focal mechanisms. We used the method estimating it from seismic moment tensor data (Matsumoto, 2016). The data were selected from focal mechanisms of earthquakes occurring from May 2016 to December 2016 at a depth range of 0-20km. We found that the stress field with strike-slip fault regime at the 0-5km depth area. This principal direction is similar to commonly observed in Kyushu Island, Japan. However, the stress field in the area deeper than 5km was in normal fault regime. The maximum principal compressional stress was close to the moderate one at the area. This area corresponds to the co-seismic large slip area estimated from the kinematic waveform inversion of strong motion data (Asano and Iwata, 2016). This suggests that the spatial change in the stress could be caused by decreasing the differential stress at the area deeper than 5km. The stress field around Hinagu fault zone was in strike-slip regime before the occurrence of the M6.5 event and changed to normal fault stress type due to the slip of the event.