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Title:: Finite Element Simulation of Lower Crustal Dragging and Fault Activity in Sichuan-Yunnan Region Constrained by GPS

作者:: 刘昌伟¹; 常祖峰¹; 李春光¹; 曾平¹; 马琳²; (1.云南省地震局,云南昆明 650224; 2.昆明理工大学,云南昆明 650000)

Author(s):: LIU Changwei¹; CHANG Zufeng¹; LI Chunguang²; ZENG Ping²; MA Lin²; (1. Yunnan Earthquake Agency,Kunming 650224,Yunnan,China)(2. Kunming University of Science and Technology,Kunming 650000,Yunnan,China)

Keywords:: Sichuan-Yunnan region; finite element simulation; dragging; strike-slip rate of faults

摘要:: 提取川滇地区GPS速度场边界值作为约束条件,依据地质资料,利用ANSYS有限元模拟软件建立川滇地区三维有限元模型,将川滇地区划分为4个块体,利用静力学分析模块模拟下地壳拖曳作用及2条主要活动断裂的走滑速率。结果显示:模型四周仅加载GPS速度场边界值,川滇菱形块体位移速度较实测速度偏差明显,不满足此地区地球动力学特征,增加下地壳拖曳作用荷载后速度场模拟结果得到优化,川滇菱形块体位移速度差值减小; 研究模拟下地壳拖曳作用产生的剪切力发现,拖曳作用在小金河断裂附近由南东转向正南时才能得到最优模拟结果,暗示其对川滇菱形块体拖曳方向发生了偏转。鲜水河、小江断裂模拟走滑速率分别为8.5 mm/a,6 mm/a,与实际走滑速率具有较好一致性,优化后可对断裂带闭锁研究提供参考。

Abstract:: Under the constraint condition extracted by the boundary value of GPS velocity field in Sichuan-Yunnan area(96°～107°E,21° ～35°N),based on geological data,we established the three-dimensional finite element model of Sichuan-Yunnan region by using ANSYS. Then we divided the Sichuan-Yunnan region into four blocks,and simulated the lower crustal dragging and the strike-slip rates of two main active faults by using the static analysis module. The results show that when only the boundary value of GPS velocity field is loaded around the model,the displacement velocity of Sichuan-Yunnan rhombic block is obviously different from the measured velocity,which does not satisfy the geodynamic characteristics of this area. After increasing the dragging load of the lower crust,the simulation results of velocity field are optimized and the difference of displacement velocity of rhombus decreases. Simulating shear forces produced by the lower crustal dragging,it is found that the optimal simulation results can only be obtained when the direction of the dragging changes from southeast to Southeast near the Xiaojinhe fault,which indicates that the direction of the lower crustal dragging is deflected. In addition,the simulated strike-slip rates of Xianshuihe and Xiaojiang faults are 8.9 mm/a and 6 mm/a respectively,which are in good agreement with the actual strike-slip rates. The optimized results can provide reference for the study of fault zone blocking.