CHARACTERISTIC ANALYSIS OF RESERVOIR INDUCED EARTHQUAKES NEARBY THE THREE GORGES DAM

Reservoir induced earthquakes of large-scale hydropower project have always a concern of owners and technical personnel. The Three Gorges reservoir has been impounded for 10 years, and the earthquake frequency in the reservoir increases significantly during the impoundment. An area near the dam site and with active faults, carbonatite and coal seams is chosen as the research object. Analyze the spatial distribution of reservoir induced earthquakes and the relationship between earthquake and reservoir water level. The analysis results indicate that 90% of the reservoir induced earthquakes are collapsing induced by earthquakes which occurred in carbonatite and coal seams. The other 10%occurred in other stratums. It also indicates that the attitude of stratum has a significant effect on reservoir induced earthquakes. The earthquakes near the dam site have clustering distribution characteristic, which mainly occurred at the northern part of Xiannvshan Fault. Some earthquakes occurred in the hanging wall of Jiuwanxi fault, which occurred more at the nearby site of Yangtze river and less in the faraway site, while rarely occurred in the heading wall of the fault. The reservoir induced earthquakes and reservoir water level are closely related. While the water level of Three Gorges reservoir rises, many small earthquakes occur on both sides of Yangtze river. When the water level rises to 175m, most of the earthquakes occur in the northern part of Xiannvshan fault and the hanging wall of Jiuwanxi fault.