Unraveling the dynamics of seismicity in the Baihetan Reservoir Area with AI-based catalog

In this study, we used LOC-FLOW to process continuous waveforms recorded by 55 stations near the Baihetan Reservoir in China, which is the second-largest reservoir in the world with installed capacity, from January 2021 to July 2022. We identified 53,838 seismic events with relative location errors within tens of meters, representing a fourfold increase compared to the manual catalog, and recalling approximately 99.0 % of the events listed therein. Our location results indicate that the seismicity after the impoundment of the Baihetan Reservoir is mainly controlled by the regional geological structure, mostly distributed on the sub-structures or fractures near the main fault. Moreover, there are significant differences in seismicity on both sides of the Jinsha River, which is attributed to the different lithology. In some areas, the seismicity gradually migrates away from the reservoir inundation zone. Some clusters exhibit significantly different migration speeds, which may be related to the mechanisms or underground structure. In addition, some events migrate along the depth which is attributed to the earthquake causing rock fractures to allow groundwater infiltration. Below the area submerged by the reservoir water, there are not only notable differences in the b-values, but also distinct correlations between water depths and earthquake rates at those different depths. This may be due to the influence of both water load and pore pressure on rocks in shallow areas, facilitating rapid stress release through microearthquakes. Conversely, in the deeper, stress accumulation results in larger-magnitude earthquakes with weak pore pressure increasing. Our results show that high-resolution earthquake catalogs can reveal the dynamic response of earthquakes to reservoirs and help understand the factors that control their distribution and magnitude. This is of great significance for future earthquake tracking in reservoir areas and for the study of other reservoirs around the world.