Japan Geoscience Union Meeting 2015

Presentation information


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

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

Thu. May 28, 2015 2:15 PM - 4:00 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:Eiji Kurashimo(Earthquake Research Institute, the University of Tokyo)

3:15 PM - 3:30 PM

[SCG57-28] Numerical modeling on intersesimic and post-seismic vertical deformation of NE Japan: Role of rheological heterogeneity

*Jun MUTO1, Bunichiro SHIBAZAKI2, Takeshi IINUMA3, Takuya NISHIMURA4 (1.Tohoku University, 2.International Institute of Seismology and Earthquake Engineering, Building Research Institute, 3.Iinuma Takeshi International Research Institute of Disaster Science, Tohoku University, 4.Disaster Prevention Research Institute, Kyoto University)

Nation wide deployment of dense geodetic network has clarified the strain accumulation and release processes through the megathrust earthquake cycle for the NE Japan subduction zone system. Prior to the 2011 Tohoku Oki earthquake, vertical deformation was characterized by rapid subsidence in the forearc and gentle uplift in the backarc. The large subsidence is only observed in a latitude range between N37 and N40 degrees. At the Tohoku Oki earthquake, coseismic vertical deformation shows a subsidence simply increasing eastward reaching a 1.2 m on the Oshika Peninsula. Post-seismic deformation over the three years shows concentric distribution of uplift and subsidence around the epicentral area: uplift in the forearc, subsidence in the volcanic front to backarc, and uplift in further backarc to Japan Sea side. The pattern of the observed uplift and subsidence across the island arc in the middle of the NE Japan, crossing the largest slip of the Tohoku Oki earthquake, is opposite that in the interseismic period (Nishimura, 2014). Here, we developed two dimensional and three dimensional finite element models of the NE Japan subduction zone to simulate the vertical crustal deformation during the megathrust earthquake cycle. Two dimensional model transects and three dimensional model includes an area of large coseismic slip of the Tohoku Oki earthquake. Temperature dependent heterogeneous viscosity structures were utilized to investigate the role of rheological heterogeneity (Muto et al., 2013). Deformation along plate boundary is the kinematically assigned using the split node method. During interseismic period, backslip is given to a locked portion at a plate convergence rate of 80 mm/year. At the coseismic step, the amount of slip corresponding to slip deficit accumulated during the interseismic period for 500 years is given along the locked portion. Our preliminary models indicate that the pattern of vertical deformation implies the rheological heterogeneity normal to the NE Japan island arc. Especially the model with presence of rheological contrast between thick, cold forearc and weak volcanic front reproduce similar pattern of vertical deformation observed in the interseismic period. Those results strongly suggest that the incorporation of rheological heterogeneity is required to explain the strain accumulation process in three-dimensional subduction zone systems from the geodetic observation.

Muto, J., B. Shibazaki, Y. Ito, T. Iinuma, M. Ohzono, T. Matsumoto, and T. Okada (2013), Geophys. Res. Lett., 40, doi:10.1002/grl.50906.
Nishimura, T. (2014), J. Disaster Res., 3, 294-302.