Abstract：Based on the seismic observation data from the Three Gorges digital seismic network, the cross-correlation and uncertainty between the seismicity and water level of the Three Gorges project in the impoundment process are systematically analyzed using the cross-correlation and rearrangement experiment technology, and the genetic mechanism of earthquakes in the Three Gorges reservoir is discussed. The results show that: 1)During the impoundment process, the crust of the reservoir head area experiences a complex process of “continuous loading-seepage saturation-rebound and rebalancing”. The spatial-temporal distribution of seismicity in the reservoir area is closely related to the temporal variation of reservoir water level. 2) From the beginning of impoundment to the 175 m experimental impoundment stage, the huge direct reservoir water load leads to the instability of mine caves, karst caves, shallow rock strata, faults and so on within 10 km along the river bank, thus inducing earthquakes. The shallow seismicity within 5 km of focal depth is obviously related to the elastic loading caused by the rapid rise of reservoir water level, showing an “instantaneous” response to the rise of reservoir water level. 3) With the stable operation of reservoir water in the 175 m experimental impoundment stage, reservoir water seepage gradually becomes the main influencing factor of seismic activity in the reservoir area, and the fault softening may be the reason for triggering the Zigui M4.5, M4.9 structural reservoir earthquakes in March 2014. The deep earthquake activity with focal depth greater than 5 km has a “lag” response to the reservoir water level. The Xiangxi reservoir section of the Yangtze river is a triangle structural area where Xiannüshan fault, Jiuwanxi fault and the Yangtze river intersect. There is a risk of medium-magnitude earthquake around this area.
MENG Qingxiao,YAO Yunsheng,LIAO Wulin et al. Analysis of the Cross-Correlation between Seismicity and Water Level at the Head Area of the Three Gorges Reservoir in the Impoundment Process[J]. jgg, 2021, 41(7): 714-720.
