FEM Numerical Simulation Of Deformation Of Strong Earthquake And Geodynamic Environment

The coseismic and postseismic deformation observed by GPS and InSAR is used as the constraints in displacement of numerical simulation. We can learn more information about the regional geodynamic environment by the calculation and the geological condition and then research the some geological processes, such as, the gestation earthquake and dynamic evolution in crust. In this paper, we get the virtual work equations of FEPG (Finite Element Program Generator) on the base of viscoelastic, poroelastic and poro-viscoelastic constitutive relationship. We calculate the coseismic and postseismic deformation using FEM. We use the GPS data of crust deformation as the constraints and obtain different Fortran programs of different questions by FEPG, and study the role of physical characters in regional geodynamic behavior.In this paper, firstly, we get the constitutive relations and other equations used in FEM calculation by FEPG. These equations are based on the theories of viscoelastic relaxation and poroelastic rebound and other researches of postseismic displacement. As the characters of observed deformation of earthquake, we use Burgers body as the viscoelastic medium, get virtual work equations used in FEPG and simulate the postseismic deformation. The postseismic displacements based on the Burgers body include three kinds of deformations, which are the elastic coseismic deformation, the exponentially-decaying short-time deformation, the linearly-increasing steady-state long-time deformation.Based on these theoretical simulation and analyses, we study the coseismic and postseismic deformation of strong earthquake in detailed.In this study, we take 1999 Mw7.6 Chi-Chi earthquake for example to study the effect of sub-fault model and layered geological crust model to the coseismic deformation. From the simulation, it is essential to use the sub-fault model composed of many small faults and layered geological crust inhomogeneous model. And then calculate the Coulumb stress change caused by Chi-Chi earthquake and analyze the relation of the Coulumb stress change and the spatial distribution of the aftersocks. After the 2001 Ms 8.1 Kunlun earthquake, postseismic displacements were resolved with GPS. The observed data showed that there were many differences between the deformations on south and north side of the Kunlun fault. And after short-time adjustment, the deformation on the north side changed direction from westward to eastward. These GPS data are used as the constraints in FEM modeling of postseismic deformation. Using 3D poro-viscoelastic model, the modeling results show that the horizontal inhomogeneous viscosities in lower crust can play an important part in geodynamic behavior. The best-fitting viscosities of lower crust about are 5.0×10¹⁷Pa.s, 9.0×10¹⁸Pa.s, respectively in Qiangtang block and Qaidam basin. This difference of viscosity of two sides of Kunlun fault is the direct reason for the differences of postseismic deformation between these two blocks. The simulation suggests that the postseismic deformation after 2001 Kunlun Ms8.1 earthquake may be caused not only by the viscoelastic relaxation but also by poroelastic rebound.And we research the cause of the short-time and long-time postseismic deformation after one earthquake. Firstly we simulate the postseismic deformation by Maxwell model. If the viscosity is lower, the relaxation is going to balance, so there is no long-term postseismic deformation. On the other hand, if the viscosity is higher, the rate of strain may be a constant. Take 1960 Chile earthquake as example, the postseismic deformation modeled with Burgers model includes coseismic deformation, transient postseismic deformation and long-term postseismic deformation. As to the calculated postseismic deformation of 1960 Chile earthquake, there is no uncoordinated phenomenon caused by the Maxwell model, when we take the Burgers model as viscoelastic medium.From our research, based on the geological condition and physical characters of crust, we can study the seismic deformation of strong earthquake using FEM numerical simulation. Then we can analyze the role of physical characters in regional geodynamic behavior by this efficient the method.