在川滇地区，GPS观测资料揭示了其运动方向为东向—东南向，呈现顺时针旋转的趋势。已有研究表明该区域的下地壳是柔性的，且运动速度快于脆性的上地壳并对其具有拖曳作用，这是造成该区域独特运动特征的主要因素。因此在数值模拟区域形变场时，仅考虑弹性作用是不够的，还需要考虑柔性下地壳的拖曳力作用。拖曳力的分布通常采用人工分区和试错法得到，主观性较强。根据川滇地区的构造活动特征建立二维有限元弹性平面模型，以GPS观测数据为约束，利用未施加拖曳力时的计算结果与实际观测结果之间的位移残差ΔUx，ΔUy与各点位坐标x，y的拟合关系式反映研究区域柔性下地壳对上地壳的拖曳力作用。计算结果表明：拖曳力主要集中在川滇菱形块体内，且块体北部的值最大，高达1.0e8 N，并以南向为主；块体南部拖曳力逐渐减小，约为4.0e7 N，方向上逐渐向东西两侧分流。拖曳力以等效体力的形式加载至模型中，可得到与实测形变场吻合度较高的结果。该方法可以为川滇地区长期地表形变动力学机制的研究提供一种物理上更加合理、方法上更加简洁的新思路。
In the Sichuan-Yunnan region, GPS observations reveal that the direction of movement is east-southeast, showing a clockwise rotation trend. In previous studies, it is noted that the lower crust of this region is ductile and moves faster than the brittle upper crust. Consequently, there is a drag force on the bottom of the upper crust, which is the main factor causing the distinct movement characteristics. Therefore, in the study of numerical simulation of regional deformation, it is not enough to consider only the elastic factor, but also the drag force. The distribution of the regional drag force is usually calculated by manual partitioning and trial and error method, which relies on subjective judgment. In this study, a two-dimensional elastic plane model is established based on the regional tectonic activities and the GPS observations as the constrained condition. The regional drag force inversion calculated through the polynomial fitting relationship between the residual values (ΔUx, ΔUy) and the coordinates of each observation point. And the residual values are the difference between the simulation result without the drag force and the observation data. The result shows that the drag force is mainly concentrated in the rhombus block, and the value in the north part is the largest (1e8 N), which is in the south direction. The drag force in the south of the block is gradually decreasing (4e7 N), and the direction is gradually diverted to the east and west sides. Finally, the drag force is applied to the finite element model in the form of equivalent body force, and the simulated result is in good agreement with the observation data. This method provides a new idea for the study of long-term deformation in Sichuan-Yunnan region, which is more reasonable and simpler.
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