Japan Geoscience Union Meeting 2015

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Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG57] Structure, evolution and dynamics of mobile belts

Thu. May 28, 2015 11:00 AM - 12:45 PM IC (2F)

Convener:*Toru Takeshita(Department of Natural History Sciences, Graduate School of Science, Hokkaido University), Hiroshi Sato(Earthquake Prediction Research Center, Earthquake Research Institute, The University of Tokyo), Koichiro Obana(Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology), Takuya NISHIMURA(Disaster Prevention Research Institute, Kyoto University), Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Aitaro Kato(Graduate School of Environmental Studies, Nagoya University), Jun Muto(Department of Earth Sciences, Tohoku University), Katsushi Sato(Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University), Shuichi Kodaira(Institute for Research on Earth Evolution Japan Agency for Marine-Earth Science and Technology), Takeshi Sagiya(Disaster Mitigation Research Center, Nagoya University), Tatsuya Ishiyama(Earthquake Research Institute, University of Tokyo), Makoto MATSUBARA(National Research Institute for Earth Science and Disaster Prevention), Yasutaka Ikeda(Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo), Chair:Tohru Watanabe(Gradudate School of Science and Engineering, University of Toyama)

11:30 AM - 11:45 AM

[SCG57-19] Spatial heterogeneities of deviatoric stress in Kyushu, Japan, inferred from the focal mechanism (2)

*Satoshi MATSUMOTO1, Takahiro OHKURA2, Masahiro MIYAZAKI1, Hiroshi SHIMIZU1, Yuki ABE3, Hiroyuki INOUE2, Manami NAKAMOTO1, Shin YOSHIKAWA2, Yusuke YAMASHITA3 (1.Institute of Seismology and Volcanology, Kyushu Univ., 2.Aso Volcanological Laboratory , Kyoto Univ., 3.Earthquake Research Institute, Univ. of Tokyo)

Keywords:stress field, Kyushu, focal mechanism

We investigated the spatial variation in stress field in Kyushu Island, southwestern Japan. Kyushu Island is characterized by existence of active volcanoes (Aso, Unzen, Kirishima, Sakurajima) and shear zone (west extension of MTL). High activity of shallow earthquakes are found not only along active faults but also in the central area of the island where there are active volcanoes. We considered the focal mechanisms of the shallow earthquakes on Kyushu Island to determine the relative deviatoric stress field. Generally, the stress field was estimated by method of Hardebeck and Michael (2006), corresponding to a strike slip regime in this area. Minimum principal compression stress (sigma-3) with its direction of near north-south dominates in the entire region. However, the sigma-3 axes around the shear zone rotated toward normal direction to the zone. This result implied the shear stress reduction at the zone and was consistent with the right lateral fault behavior along the zone detected by strain rate field analysis for GPS data. On the other hand, normal faulting stress field dominates in Beppu-Shimabara area located middle of the island. This result and direction of sigma-3 are consistent with formation of Unzen graben and Hohi volcanic zone in the area.