资源环境科技发展态势分析平台

Earthquakes induced by reservoir impoundment pose great risk to property and lives worldwide, but studies demonstrating relationships between reservoir water levels, specific faults, and the local geology are rare. Here we show that the 2013 M5.1 Badong Earthquake, the largest earthquake so far in the Three Gorges Reservoir (TGR) region of China, occurred at a shallow depth on a right-lateral south-dipping strike-slip fault. The fault is at least 15km long and intercepts the TGR at the NS-running Shennongxi River. We find that the earthquake and its foreshocks and aftershocks are confined to a fractured Triassic carbonate formation that crops out in the reservoir. The precise locations of earthquakes coupled with the local geology suggest that the sequence was induced by high pore pressure due to reservoir water infiltration in a specific rock type. The newly identified fault has the potential to generate earthquakes of magnitude approaching the designed seismic intensity limit of the Three Gorges Dam.

Plain Language Summary Earthquakes induced by reservoir impoundment pose great risk to property and lives worldwide, but studies demonstrating relationships between reservoir water levels, specific faults, and the local geology are rare. In this study, we determined focal mechanism and depth of the 2013 M 5.1 Badong Earthquake, the largest earthquake so far in the Three Gorges Reservoir (TGR) region of China. We also obtained high-precision locations of 205 events in this earthquake sequence. The results show that these earthquakes occurred at shallow depths between 1 and 5km on a steep south-dipping fault. The fault is at least 15km long and intercepts TGR at the NS-running Shennongxi River. A field survey indicates that the earthquakes are confined to a fractured rock formation that crops out in the reservoir. The precise locations of earthquakes coupled with the local geology suggest that they were induced by high pore pressure due to reservoir water infiltration. The newly identified fault is a seismic risk to the Three Gorges Dam. The findings are important because (1) they highlight the importance of understanding the detailed local hydrologic system in risk assessment, and (2) the fact that the seismogenic fault was missed before demonstrates the limitations of preconstruction risk-assessment surveys.