# Numerical Simulation of the Influence of the Baihetan Reservoir Impoundment on Regional Seismicity
## 6 Conclusions  
This study calculates the deformation, stress, and pore pressure on major faults in the Baihetan Reservoir after the impoundment. The \(\Delta\)CFS of major faults is quantified, and the seismicity changes of major faults are analyzed and discussed together with observed seismic records. Moreover, the influence of reservoir impoundment on the localized seismicity is explored. The following conclusions are drawn:  
1. Pore pressure diffuses downward with the gradual increase of reservoir water level, and the compressive effect of water load gradually increases. The stress is mainly related to relative position and fault geometry. The compressive effects of water load and pore pressure jointly determine regional stress changes.
2. During the reservoir impoundment period, the \(\Delta\)CFS varies in different faults. The positive value always leads to an increase in seismicity. The seismicity has increased since the reservoir impoundment, and most of the earthquakes are \(M\leq 2.0\). This may be due to small regional stress accumulation.
3. Reservoir-induced earthquakes usually occur below the reservoir center, and the impoundment mildly affects earthquakes far from the center. The influence of impoundment on the \(M_{8}4.3\) Qiaojia earthquake is less than the typical threshold of a triggered earthquake. It is a natural event.
4. The long-term effect of reservoir impoundment has little impact on regional stress. The effect of viscosity relaxation of the strata on fault stress is much less significant compared to tectonic loading. Seismicity around the reservoir will stabilize once the pore pressure and flow field reach equilibrium.  
Conceptualization, Z.W.; methodology, Z.W., H.Z., and Q.M.; validation, Z.W., H.Z., Y.G., and Q.M.; writing--original draft preparation, Z.W.; writing--review and editing, Z.W., H.Z., Y.G., and Q.M. All authors have read and agreed to the published version of the manuscript.  
Figure 9: The normal stress evolution of key faults after reservoir impoundment. Case 1 uses the material parameters in Table 2. Case 2 reduces the mantle viscosity to \(1.4\times 10^{22}\) Pa-s. Case 3 reduces the crust viscosity to \(0.5\times 10^{25}\) Pa-s.  
Funding: This study was supported by the Central Public-interest Scientific Institution Basal Research Fund (No. CEAIEF20230209), the National Natural Science Foundation of China (U2039207, U2239205), and the Fundamental Research Funds for the Central Universities. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Data for this paper are provided by the National Earthquake Data Center of China, which is accessible from the following link: [[https://data.earthquake.cn/datashare/report_shtml?PAGEID=earthquake_zhengshi](https://data.earthquake.cn/datashare/report_shtml?PAGEID=earthquake_zhengshi)]([https://data.earthquake.cn/datashare/report_shtml?PAGEID=earthquake_zhengshi](https://data.earthquake.cn/datashare/report_shtml?PAGEID=earthquake_zhengshi)) (accessed on 6 March 2024). Conflicts of Interest: The authors declare no conflicts of interest.