The Numerical Simulation Study Of The Dynamic Process Based On Longmenshan Fault Over Earthquake Cycles

Located in the east of Tibetan plateau,longmenshan fault zone is one of the largest thrust belts in southern china with the adjacence of Sichuan basin.The wenchuan Ms8.0 earthquake had put a great destory to the lives and properties of our motherland country in 2008.After that,how to simulate the earthquake-cycling behavior of longmenshan fault zone numerically,and further the analysis of the exact position where earthquakes breeded and happened to explore the relative dynamic questions,such as the accumulation and release process of stress-strain in different stages of earthquake cycles,are the main tasks of our research.Taken the substantial data of GPS,geologic investigation,geophysical detection,tectonophysics experiment results and the researching findings of earthquake cycles on longmenshan fault zone for reference,a good restriction can be made to the 2-D finite element model on its geometric structure,medium parameters,fault geometry and friction coefficient on the fault.And an investigation had been made to find the current status of lithosphere medium structure surrounding the longmenshan fault zone at home and abroad,in order to provide the adjustable range of medium paremeters in our research.Taking into account of the gravity of the model and rate-state friction law on fault,we make full use of the GPS data accumulated around the longmenshan fault zone as the boundary conditions and introduce the plasticity condition of the upper crust of Songpan-Ganzi block to establish the 2-D elastoplasticity-viscoelasticity finite element model.Based on the numerical simulation of stress-strain evolution over large earthquake cycles,we find that:(1)Quasi periodicity of earthquake cycles is emerged in the simulation.(2)the maximum Coulomb stress and Mises stress accumulating and releasing locate in the depth of 17 km-20 km,where probably is the nucleation region on the fault.(3)The coseismic slip and Coulomb stress release show a disparity between the upper and lower part of the fault rupture,with larger slip and lower stress release near surface and smaller slip and greater stress release at down dip of the fault rupture,which is consistent with seismic and geodetic coseismic study results.(4)Tectonic stress and strains are accumulated interseismically,and released partially by periodical and partially by the permanent deformation and folding in upper crust.(5)the dynamic procession of earthquake cycle is demonstrated clearly by the strain energy density increment patterns during the interseismic,coseismic and poseismic periods.(6)Strain energy also accumulated within the lower part of the seismogenic layer during the coseismic time period,and could be released postseismically through aftershock and viscous deformation close to fault around the downdip end of the fault rupture.The simulation research of this article will help us comprehend the deformation pattern of tectonic zone over the eastern part of Tibet plateau and its dynamic process quantitatively.