Three-dimensional Finite Element Numerical Simulation Of Present Crustal Deformation In Sichuan - Yunnan Region By GPS Constraint

Sichuan-Yunnan region is located in the southeast margin of Tibet plateau,due to the extrusion of the Indian plate northward,due to the complex geological structure and the region of strong crustal deformation,is one of the most significant regional seismicity in China mainland,so the Sichuan-Yunnan area has been the focus of the GPS crustal deformation monitoring and research areas,but at present the study of the region are mainly composed of kinematics,as a result of the earthquake gestation and occurrence and deep crust structure,properties,characteristics and evolution laws of closely related,therefore to carry out the numerical simulation of the crustal deformation is of great significance to promote the earthquake prediction research.In this paper,the finite element numerical simulation method,with 22°N³4°N,96°E¹06°E as the study area,based on the analysis of the geological structure and seismic activity,the main active blocks in Sichuan-Yunnan region and fracture distribution and the latest-the upper mantle of the earth's crust velocity structure characteristics?Yao Huajian,etc.,2020?,build a three-dimensional finite element model of the region,and then use high precision GPS deformation field of Sichuan-Yunnan region from 2009 to 2015 calculated by Min Wang?2020?to constraint of model boundary conditions,to carry out the numerical simulation,Using different geophysical model?parameters?,on the basis of the fitting precision of GPS deformation field,research mainly large fault deformation on overall regional structure,the influence of the horizontal and vertical inhomogeneity of medium on the whole the influence of the crustal deformation and the influence of viscous medium parameters on the crustal deformation,the last in the region of seismic risk has carried on the simple analysis of the assessment.The main work and conclusions of this paper are as follows:1.Based on the block activity theory,the distribution of faults and GPS stations,and the crust-upper mantle wave velocity model,the three-dimensional finite element model of the Sichuan-Yunnan region is constructed.The model has a length of about 1333km from east to west,a length of about 1000km from north to south,and a depth of 100km.It contains 9 major active faults and is composed of 430080 units and 77,696 nodes.2.Based on 3d uniform stratification model 1,the latest GPS deformation field,fault slip rate and locking depth are used as constraints for numerical simulation,which shows that the crustal deformation pattern in the study area is not only constrained by the overall GPS boundary conditions,but also closely related to the movement characteristics of the fault itself.3.Build the three dimensional inhomogeneous stratified model 2 which the crust-upper mantle stratification and its dielectric parameters are fully considered,under the same constraint conditions,the accuracy of the model significantly higher than the uniform three-dimensional layered model 1,the simulation results show that the mean square error of GPS sites east-west speed value by 1.932 mm/a reduced to 1.682 mm/a,north and south to the speed of the mean square deviation value by 2.728 mm/a reduced to 2.493 mm/a,that medium horizontal and vertical inhomogeneity of active blocks in Sichuan-Yunnan region of effect to the whole crustal deformation.4.In the three dimensional inhomogeneous stratified model 2,on the basis of the south China block in the lower crust and upper mantle structure viscous coefficient is set to10²⁰ and10²²Pa·s?Model 3?,deformation simulation results show that the east-west speed is 1.674 mm/a value of the mean square error,the north and south to speed the mean square deviation of a value of 2.477 mm/a,show that south China massif Sichuan-Yunnan block has a hard crust structure.5.Using three-dimensional finite element model 3,15 km depth of the earth's crust stress field are simulated,the results show that the stress concentration mainly occurred in the border along the fault zone and fracture,the direction of fault movement speed and geometry changed significantly in the region,such as the junction of Xianshuihe fault and Ganzi-Yushu fault,the junction of Xiaojiang fault and Honghe fault,the junction of Zemuhe fault and Xiaojiang fault have been major earthquakes of magnitude 6 or above,so these areas of seismic risk is bigger,deformation and earthquake activity monitoring and analysis of research should be strengthened.