Study On Fault Reactivation Feature Of Xiannvshan-jiuwanxi Fault Zone In The Head Area Of The Three Gorges

Fault reactivation is defined as relatively stable fault has been reactivated or get enhanced activities which is caused by some external factors.The Three Gorges reservoir is the major construction of a great achievement-the Three Gorges project in China,and the fault activity in the head area has been obviously enhanced since impoundment started in the May,2003.As the key research object of the crustal stability and reservoir-induced seismicity from the Three Gorges Project demonstration period,there are more than 3 times of earthquakes with magnitude 4 or higher happened at the Xiannvshan-Jiuwanxi fault zone.Therefore,in order to ensure the normal operation of the Three Gorges Project and the safety of people's lives and property in the middle and lower reaches of the Yangtze,it is significant to study the seismic response to the fault zone under the action of reservoir water.On the basis of previous studies,through field geological survey,fault gouge experiment and numerical simulation,the property of activity of the fault zone and the characteristics of fault reactivation under the action of reservoir water are discussed in this paper.This paper has done the main work of four parts:1.Collect the geological,tectonic,geophysical and seismic activity data in the head area of the Three Gorges Reservoir area.By comparing with the seismic activity before and after the impoundment in the reservoir area,this paper analyzes the characteristics of seismic activity in the area from several aspects such as the spatial distribution,the strength,and the relationship between the reservoir water level and so on.2.We investigated geometry and activity features of the Xiannvshan-Jiuwanxi fault zone.Using the fault gouge samples we collected,we did SEM experiment,eparticle size xperiment and X-ray diffraction experiment on the fault gouge samples,and the activity intensity,activity ages and activity character of the fault are discussed.3.Based on the data of topography,hydrology and engineering geology in the head area of the Three Gorges reservoir,the 3D geological model was fianlly established.According to the annual periodic variations of the water level of Three Gorges reservoir,we simulated reservoir water permeability distribution and strength characteristics under different water level in Xiannvshan-Jiuwanxi fault zone.The influence of reservoir water seepage on the fault zone is discussed through these simulation results.4.Based on the above research,the active features of the Xiannvshan-Jiuwanxi fault zone have been analyzed,also the influence of reservoir water on the fracture and the possibility of fault reactivation have been discussed.