HR: 1340h
AN: G13A-0786    [Abstracts]
TI: FEM modeling of postseismic deformation of poroelastic material
AU: * Kawamoto, S
EM: satoshi@eps.nagoya-u.ac.jp
AF: Nagoya University, Graduate School of Environmental Studies, Nagoya University Furo-cho, Chigusa-ku, Nagoya City, Aichi, 464-8602, JAPAN, Nagoya, 464-8602 Japan
AU: Ito, T
EM: take@seis.nagoya-u.ac.jp
AF: Nagoya University, Graduate School of Environmental Studies, Nagoya University Furo-cho, Chigusa-ku, Nagoya City, Aichi, 464-8602, JAPAN, Nagoya, 464-8602 Japan
AU: Hirahara, K
EM: hirahara@eps.nagoya-u.ac.jp
AF: Nagoya University, Graduate School of Environmental Studies, Nagoya University Furo-cho, Chigusa-ku, Nagoya City, Aichi, 464-8602, JAPAN, Nagoya, 464-8602 Japan
AB: Following a large earthquake, postseismic deformation in the focal region has been observed by GPS, leveling measurements and the other geodetic measurements. To explain the postseismic deformation, researchers have proposed and well investigated two physical mechanisms of afterslip and viscoelastic relaxation. In some cases, however, there have been observed postseismic deformation which can not be explained by these mechanisms. Therefore, another mechanism has been proposed, where the crust is treated as "poroelastic material". This concept is called "poroelasticity". In this concept, postseismic deformation is caused by pore fluid flow due to the coseismic stress redistribution. We explored, therefore, the postseismic deformation due to pore fluid flow in a poroelastic material using finite element method (FEM), which can easily handle lateral variations of hydraulic diffusivity and elastic or plastic property. We used the FEM program 'CAMBIOT3D' originally developed by Geotech. Lab. Gunma University, Japan (2003). Because this program was developed for soil mechanics, we must have modified so as to calculate deformation due to earthquake faulting. We implemented the 'split node technique' (Melosh and Refsky, 1981) to calculate the coseismic deformation. In addition to this, we modified the program to calculate the deformation taking into account the Skempton's B. This coefficient B determines what fraction of the coseismic stress due to an earthquake is allotted to pore pressure. Without Skempton's B, coseismic pore pressure becomes too large and hence postseismic deformation is calculated too large. We evaluated the postseismic deformation in a poroelastic material to show that the poroelastic deformation is quite different from that of afterslip and viscoelastic relaxation models. In this presentation, we show the postseismic deformation due to pore fluids flow in a poroelastic material and the effect of Skempton's B. Especially, we discuss what different pattern of postseismic deformation is produced depending on the lateral variation of hydraulic diffusivity structures in and around the fault zone, which structures have been differently inferred from fault zone core sampling researches and so on.
DE: 1734 Seismology
DE: 1242 Seismic deformations (7205)
DE: 0902 Computational methods, seismic
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting