# Numerical Simulation of the Influence of the Baihetan Reservoir Impoundment on Regional Seismicity
## 3 Model  
We utilized the self-developed program to generate the three-dimensional pore-viscoelasticity finite element numerical model of the Baihetan Reservoir area (Figure 1(a)), which mainly contains the Zemuhe Fault (ZMHF), Daliangshan Fault (DLSF), Lianfeng Fault (LFF), Ninghui Fault (NHF), Puduhe Fault (PDHF), north part of the Xiaojiang Fault (XJFI), Xiaojiang Fault (XJF2), and Zhaotong-Ludian Fault (ZLF). According to [PERSON] et al. (2020) [26], fault geometry has a certain influence on stress distribution in porous media. The fault geometry in the study area is incomplete. The fault geometry used in calculations is presented in Table 1. We assigned a vertical strike-slip mechanism to the unspecified faults due to the high fault dip in this area. In this example, we utilized four nodes to generate grid files in parallel (Figure 1), which can effectively improve the speed of model generation. Firstly, the study area was divided into multiple subregions (Figure 1(b) takes four subregions as examples), and the vertical grid of each subregion was generated based on the thickness of each stratum and the predefined grid density. At the same time, the grid nodes were adjusted using real terrain data. Finally, the subregional grids were summarized to form an overall grid. The parallel mesh generation program can effectively enhance the calculation speed for complex terrains and boundary conditions, significantly improving the efficiency of mesh generation.  
According to [PERSON] et al. (2021) [PERSON] et al. (2021) [PERSON] et al. (2021), we divided the 30 km depth model into four layers, and the material parameters are shown in Table 2. SRTM30 interpolates the surface, and the boundary conditions of the fixed normal and free tangential direction are set on the model's surroundings and bottom. The variations of the strain and stress are calculated from the beginning of water injection for 200 years from 2021 to 2221, and the initial response to  
Figure 2: The model and mesh with boundary conditions. (**a**) The model has fault distribution and different layers. I (A–A\({}^{\prime}\)) and II (B–B\({}^{\prime}\)) represent the northern segment and southern segment of the Xiaojiang Fault, respectively. (**b**) The subarea in mesh partition; four partitions are taken as an example in b. The surrounding and bottom normal displacement and pore pressure are fixed, and the pore pressure and the water load on the upper surface are determined by the water level and topography. Different colors represent grids generated by different nodes.  
the impoundment is mainly calculated from April 26 to 23 September 2021, a total of 150 days after the initial water storage. Since the impoundment began, the water level of the reservoir has been steadily rising and has now stabilized at a high level. Thus, the part of the surface DEM (Digital Elevation Model) below the water level will be subjected to a pressure of size \(p=\rho g\Delta h\) and a face force of size. \(T_{z}=\rho g\Delta hds\), where \(\rho\) is the water density, \(g\) is gravity, \(\Delta h\) is the difference between DEM and water level, and \(ds\) represents the unit area.