Abstract: 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.

Key words: Sichuan-Yunnan region, drag force, polynomial fitting, finite element simulation