Numerical Simulation Of Coseismic And Post-seismic Deformation Of 2008 Wenchuan Earthquake And Its Effect On Geological Hazards

We calculated the coseismic and post-seismic deformation of the 2008 Wenchuan earthquake in Longmenshan area using PSGRN/PSCMP.We then analyzed the deformation adjustment of Songpinggou area caused by Wenchuan earthquake.The results show that the Wenchuan earthquake has a certain influence on the surface deformation in Songpinggou zone,which leads to the surface topography gradient of Songpinggou becoming larger and makes the topography change in the direction conducive to the formation of landslides,and this influence continues in the post-seismic deformation stage.The adjustment of seismic deformation should be considered in the analysis of landslide hazard in areas with low trigger threshold.Since PSGRN/PSCMP cannot consider the horizontal inhomogeneity of the medium model,we use the Pylith FEM software to establish a dislocation model.Considering the inhomogeneity of the medium,we study the influence of the crustal structure on the earthquake coseismic and post-seismic deformation.Compared with PSGRN/PSCMP,Pylith can consider the non-uniformity of physical properties and geometric shape in the horizontal direction of medium.An ideal dislocation model is established to calculate the effects of fault dip angle,elastic layer thickness and viscosity on the co-seismic and post-seismic deformation.The results show that the smaller the fault dip angle of the thrust fault,the larger the co-seismic and post-seismic deformation amplitude and deformation range of the groundsurface,and the fault dip angle of the seismogenic fault is inversely proportional to the amplitude and deformation range of the surface deformation adjustment.The thickness of elastic layer has little effect on the co-seismic deformation of thrust fault,but it mainly affects the post-seismic deformation adjustment.For the deformation adjustment area,the thinner the elastic layer is,the greater the post-seismic deformation adjustment per unit time is.The coefficient of viscosity has little effect on the coseismic deformation of the surface,but mainly affects the adjustment of the surface deformation after the earthquake.The larger the coefficient of viscosity of the viscoelastic layer is,the smaller the adjustment amplitude and range of the surface deformation.For the coseismic and post-seismic deformation of the thrust fault,the smaller the effective elastic thickness of the upper wall of the fault is compared with the footwall,the lower the effective viscosity of the lower crust and mantle is,and the larger the range of the post-seismic deformation of the hanging wall is.However,the dip angle of fault surface affects the distribution characteristics of coseismic and generally formed on the hanging wall side.Combined with the co-seismic and post-seismic landslide distribution laws of the Wenchuan earthquake,the study shows that the relatively thin effective elastic thickness of the Songpan-Ganzi block and the low effective viscosity of the lower crust and mantle are the important deep dynamic reasons for the large deformation and serious geological disasters on the hanging wall of the Wenchuan earthquake.At the same time,the second Ux displacement extreme area on the side of the hanging wall far away from the surface fault line may be the deep dynamic of the Xinmo landslide 9 years after the Wenchuan earthquake(2017).