Potential seismicity by impoundment of the Baihetan Reservoir, Xiaojiang Fault Zone, Southwest China

Abstract

Baihetan reservoir, the second-largest hydropower station in China, is located at the east boundary of the Sichuan-Yunnan block, one of the most seismic active zones in continental China. Many studies have shown that the potential risk of reservoir-induced seismicity will ramp up when the crustal stress field is remarkably perturbed following its impoundment. In this work, based on the fully-coupled poroelastic theory, we built models with different parameters to quantitatively analyze the displacement and stress field changes caused by the Baihetan reservoir impoundment. The preliminary results show that the maximum subsidence reaches about 0.3 m, and the stress change is about 0.4 MPa at 5 km after five years of impoundment. Most strikingly, we find a significant increase of Coulomb Failure Stress Change (ΔCFS) on the fault planes at the vicinities of the surrounding Xiaojiang Fault, Daliangshan Fault, and Lianfeng Fault, suggesting high reservoir induced seismicity risks. However, the occurrence of induced/triggered earthquakes is not only related to the regional tectonic loading, but also the rock strength. Moreover, the reservoir water level rise rate will lead to different spatial–temporal patterns of the induced micro-seismicity, however, this difference will gradually disappear as the reservoir continues to operate, and the large earthquake is mainly affected by geological tectonics.