Japan Geoscience Union Meeting 2018

Presentation information

[EJ] Oral

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

[S-CG57] Dynamics in mobile belts

Tue. May 22, 2018 1:45 PM - 3:15 PM A05 (Tokyo Bay Makuhari Hall)

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), Chairperson:Iwata Takaki, Shibazaki Bunichiro

3:00 PM - 3:15 PM

[SCG57-06] Modeling deformation and stress state in the San-in strain concentration zone

*Bunichiro Shibazaki1, Takuya Nishimura2, Yoshihisa Iio2, Takumi Matsumoto3 (1.International Institute of Seismology and Earthquake Engineering, Building Research Institute, 2.Disaster Prevention Research Institute, Kyoto University, 3.National Research Institute for Earth Science and Disaster Resilience)

Keywords:San-in strain concentration zone, Deformation, Stress state

Recent GNSS observations have revealed various strain concentration zones: Niigata-Kobe, Tohoku Sekiryo, San-in, and Kyushu. The many recent large earthquakes occurred in the strain concentration zones; therefore, it is important to understand the mechanisms of these zones to understand the generation processes of large earthquakes. It is thought that strain concentration zones are developed by weak rheological structure due to the existence of water, high temperatures, and the preexistence of weak structures, such as ancient rifts. Recently, Nishimura and Takada (2017) found a right-lateral San-in strain concentration zone, in which the 2016 central Tottori earthquake occurred. This study models the San-in strain concentration zone by considering the heterogeneous rheological structure using a finite element method with nonlinear viscoelasticity and Mohr-coulomb plasticity.

First, we generate a lithostatic stress state. We then set the boundary conditions, which cause the strike-slip stress regime. We assume the temperature increases with depth using the observed geothermal gradient distribution. Geothermal gradients are high along the volcanic region. Our model generates a strain concentration zone along the high geothermal gradient zone. Furthermore, small faults are generated in a direction almost perpendicular to the strike of the strain concentration zone when the accumulated shear stain is small. This model explains the faulting process of the 2016 central Tottori earthquake, the strike of which was almost perpendicular to the strike of the San-in strain concentration zone. The model also explains the fault development of the 1943 Tottori earthquake. This model set the azimuth of the maximum horizontal stress axis at N110°E. Due to the development of the strain concentration zone, the azimuth of the maximum horizontal stress axis rotated from N110°E to N130°E in the strain concentration zone. The results are consistent with the observed stress state obtained by Kawanishi et al. (2009).