Assess the reservoir-induced seismic hazard in the Hubei section of the three Gorges reservoir using gray clustering method

In this paper, a statistical analysis is made using the gray clustering method on the earthquake inducing factors, such as dam height, storage capacity, regional stress state, fault activity, lithology medium conditions and seismic activity background, based on a database of reservoir-induced earthquakes, which includes 150 reservoir-induced earthquake cases and 532 large reservoirs data. Corresponding earthquake occurrence ratios are obtained and used as predictors for reservoir-induced earthquakes. According to the six quake-inducing factors, assessment is made on the maximum magnitude of reservoir-induced earthquake for the Three Gorges Reservoir dam area, the bayou of Xiangxi stream and the cross-river section of the Xiannushan Fault zone, the west Xietan, Badong, and on both banks of Shenlong stream. The results show that the upper-limit of magnitude at dam area is less than magnitude 3, that at the bayou of Xiangxi stream and the cross-river section of Xiannushan Fault zone is between magnitude 4~5, that at west of Xietan is less than magnitude 3, and that at the northern bank of badong and on both banks of the Shenlong stream is between magnitude 3~4. The results have been validated by the actual reservoir-induced seismicity after the impoundment of the Three Gorges Reservoir, with the ML 2 earthquake at Xiaoxikou 4 km far away from the dam of the Three Gorges Reservoir on February 6, 2009, the MS 4.1 earthquake at the bayou of Xiangxi stream and the cross-river section of the Xiannushan Fault zone on November 22, 2008, the MS 2.6 earthquake at the west Xietan on August 22, 2009, and the ML 3.5 earthquake at the bank of Shenlong stream on December 14, 2009.