Remote dynamic triggering of reservoir-induced seismicity during the initial impoundment of the Baihetan Reservoir

The Baihetan Hydropower Station, located on the eastern margin of the Tibetan Plateau, is the world's second-largest hydropower station in terms of installed capacity. The 289-meter-high dam will create a massive reservoir with a storage capacity of 20.6 billion cubic meters upstream of the Jinsha River. On April 6, 2021, the Baihetan Reservoir began its initial impoundment, leading to significant seismic activity at the intersection of the Xiaojiang, Zemuhe, and Daliangshan fault zones. These earthquakes were characterized by shallow focal depths and a general distribution along the reservoir area, indicating reservoir-induced seismicity. During the initial impoundment of the Baihetan Reservoir, two notable earthquakes occurred within the Tibetan Plateau, the Yangbi MS 6.4 earthquake and the Maduo MS 7.4 earthquake, with an interval of less than five hours between them.

This study utilizes data from a dense seismic array deployed in the Baihetan Reservoir area to analyze the remote dynamic triggering effects of these two earthquakes. Preliminary works indicate that the surface waves from the Yangbi MS 6.4 earthquake, which was approximately 330 km away, did not trigger any small earthquakes in the Baihetan Reservoir area, and there was no significant increase in microseismic activity within four hours after the earthquake. In contrast, the surface waves from the Maduo MS 7.4 earthquake, which was about 920 km away, triggered multiple small earthquakes when they reached the Baihetan Reservoir area. Additionally, precise earthquake relocations reveal the heterogeneous distribution of critical stress states in the Baihetan Reservoir area due to the impoundment process. These results provide insights into the mechanisms of reservoir-induced seismicity and the potential for remote dynamic triggering in the region.