Cascade effects of triggered earthquakes of cascade dams: Taking Xiluodu and Xiangjiaba reservoirs as examples

This study investigates the perturbations of the surrounding stress field caused by the cascade effect of Xiluodu and Xiangjiaba reservoirs after impoundment and a three-dimensional pore-elastic coupling model of the impoundment of cascade reservoirs are established. The finite element method calculates the pore pressure field, elastic stress field, and variation of Coulomb stress on local faults. The results show that: 1) the spatial distribution of the earthquake cluster is obviously consistent with the area where the pore pressure increases; 2) The ΔCFS at the epicenters of the April 2014 Yongshan M_L5.1 earthquake and the August 2014 Yongshan M_L5.2 earthquake imparted by the reservoirs are: 0.67kPa and 10.87kPa, respectively, indicating that impoundment promotes these two earthquakes at different levels, and the latter is more significant; 3) The elastic stress field change imparted by the impoundment of Xiluodu reservoir has an impact on the Xiangjiaba Reservoir in the early stage. However, the earthquakes between two reservoirs are possibly triggered by the latter. The Xiangjiaba reservoir increases the pore pressure in its upstream part by 1.0 kPa; 4) the impoundment of the reservoirs increases the seismic risk of the southern section of the Yanfeng fault and the middle section of the Lianfeng fault, while the Manao fault is less affected.