Spatial‐Temporal Pore Pressure and Stress Evolution Associated With the Impoundment of Two Contiguous Reservoirs in Jinsha River, China and Regional Seismicity

The Xiluodu‐Xiangjiaba Cascade Reservoirs have been built in the lower reaches of the Jinsha River, Yunnan Province, China since 2012. Following the impoundment of these two contiguous reservoirs, widely felt seismicity has been recorded along the mainstream of the river, including three events with magnitudes greater than 4.5. To explore the correlation between the evolution of stress induced by reservoir impoundment and the spatial‐temporal seismicity, we establish a three‐dimensional poroelastic finite element model and compute the stress changes due to the elastic load of reservoir water storage and pore pressure diffusion based on the fully‐coupled poroelastic theory. The results show that the hypocenters of earthquakes after impounding are spatially correlated with the pore pressure increase. The Coulomb failure stress changes (ΔCFS) resolved on both nodal planes of the focal mechanisms of the three events with magnitudes greater than 4.5 suggest that the increased pore pressure could lead to significantly positive ΔCFS and contribute to the occurrence of the three events. Further investigation indicates that pore pressure and ΔCFS on active faults close to the river mostly increase after impounding, probably enhancing the regional seismicity. The pore pressure on active faults close to the Xiluodu Reservoir shows a clear seasonal variation. Our study reveals that the faults and geologic anomaly bodies with high permeability could provide preferential diffusion channels, thereby controlling the spatial‐temporal evolution of pore pressure changes and affecting the seismicity distribution, which are essential to understanding the occurrence of earthquakes far from the reservoir.