Numerical simulation of the seismic responses to Baihetan Reservoir impoundment

Baihetan Reservoir, currently the second largest hydropower project in China in terms of power generation capacity, is located between the Sichuan-Yunnan block and South China block, where multiple large faults converge, including the Xiaojiang, Zemuhe, and Daliangshan faults. After impoundment, the earthquake distribution surrounding the reservoir showed high spatiotemporal correlation with water level changes. Quantifying the impact of impoundment on the current and future seismic responses of large fault zones is important for evaluating seismic risk. Here, we established a 3D poroelasticity model for Baihetan Reservoir and surroundings using the finite element method. Coulomb stress changes for major faults were calculated based on actual water level changes. Following impoundment, the Coulomb stress increase on the Xiaojiang fault reached 0.07 MPa at < 5 km depth, indicating substantial promotion of seismicity. Conversely, the Coulomb stress increased minimally (1–10 kPa) on the Zemuhe and Daliangshan faults, and decreased on some fault segments (e.g. the Zhaotong-Ludian fault). Generally, seismic responses were concentrated at < 10 km depth and weakened substantially with increasing depth. Our results highlight the need for further research and monitoring of the Xiaojiang fault.