Japan Geoscience Union Meeting 2018

Presentation information

[EJ] Poster

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

[S-CG57] Dynamics in mobile belts

Wed. May 23, 2018 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Toru Takeshita(Department of Natural History Sciences, Graduate School of Science, Hokkaido University), Hikaru Iwamori(海洋研究開発機構・地球内部物質循環研究分野)

[SCG57-P18] Characteristics of the seismic gap in west part of the central Kyushu, Japan

*Yuhei Yuasa1, Satoshi Matsumoto2, Shigeru Nakao3, Takeshi Matsushima2, Takahiro Ohkura4 (1.Department of Earth and Planetary Sciences,Graduate School of Sciences,Kyushu University, 2.Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, 3.Department of Earth and Environmental Sciences, Graduate School of Science and Engineering, Kagoshima University, 4.Aso Volcanological Laboratory, Institute for Geothermal Sciences, Graduate School of Science, Kyoto University)

The seismicity in Amakusa islands located at west part of Kyushu Island, Japan is much lower than other part of Kyushu. Investigating characteristics of the seismicity gap is important for knowing the mechanism of earthquake generation. Here, we conducted analyses to consider cause of the gap and effect on the surrounding area.
In this study, we considered three models to explain the low seismicity. (1) high strength model: elastic property is much higher than the surrounding area. (2) weak zone model: no brittle failure occur in the area because of weak strength, and (3) low shear loading model: weakening shear stress loaded to the region due to inelastic deformation in the surrounding area. For verifying reliability of models (1) and (2), we considered an infinite elastic plate with a circular inclusion having different elastic constants from surrounding infinite plate. And then, we compared the spatial pattern of strain based on two dimensional theoretical equation by Nishimura and Sezawa (1931) with that of observed strain rate obtained from the GNSS network. For model (3), we calculated the distribution of the inelastic strain rate due to the earthquakes using the method of Kostrov (1974). The results reveals that the crustal deformation around Amakusa islands can not be explained by the models (1) and (2). Therefore it seems the model (3) is presumable because the region with the high inelastic strain rate(~10-8 /yr ) is seen to surrounding Amakusa islands. However, we need to revise the model (3) by taking into account the estimated stress field, velocity structure, and viscous structure in the Kyushu obtained by previous study.