Four large hydropower stations have recently been built downstream the
Jinsha River in Southwestern China with a strong regional tectonic
activity background. There is widely felt seismicity since the
impoundment of the Xiluodu and Xiangjiaba reservoirs, increasing the
public concern in this region. We begin with a criticality analysis of
the faults near these reservoirs to quantify their susceptibility to
triggered seismicity. Then we focus on the Xiluodu reservoir to
investigate the correlation between the impoundment and seismicity
nearby. We analyze the spatio-temporal distribution of seismicity near
the Xiluodu reservoir, and identify the plausible rapid and delayed
seismic response due to the impoundment. According to the impoundment
record, we explicitly model the hydro-mechanical changes due to
diffusion and reservoir water load, i.e., in pore pressure, elastic
stress, and the resulting Coulomb stress. Our results show that the pore
pressure changes can reach a level that may trigger fault reactivation
and consequently, seismicity nearby. The water load can also induce the
positive Coulomb stress changes on faults, depending on the fault
orientation, which is especially important for understanding the
earthquakes that occurred shortly after the impoundment and at more than
10 km distance from the reservoir. The combination of these two effects
can induce positive Coulomb stress change over a larger area, which
overlaps the majority of the events after the impoundment. While the
causal relationship between the impoundment and seismicity warrants
further analysis, we hope to inform the regional seismic impact of
impoundment with this timely study.