Regularity Research And Trend Prediction On Reservoir Earthquake Of The HuBei Section In The Three Gorges Reservoir Area

The impoundment of large-scale reservoirs will break the various geological and mechanical balances naturally formed in the reservoir area and cause a series of new geological environmental problems.Among them,reservoir earthquakes are one of the reasons for the aggravation of geological disasters in the reservoir area.Since the impoundment of the Three Gorges Reservoir,a large number of reservoir earthquakes have occurred around the Yangtze River.it has reached ten thousands of times,including 7reservoir earthquakes with magnitude greater than 4.0 and the maximum magnitude is 5.1.Reservoir earthquake not only affects the safe operation of hydraulic structures,but also has an important impact on the deformation and stability of the bank landslide.These frequent mid-to-low intensity reservoir earthquakes can directly cause the deformation and destruction and can also aggravate the long-term damage effect of the rock and soil mass of the bank landslide in the area.These ultimately lead to the destruction of the bank landslide.At the same time,the secondary geological disasters caused by the collapse of karst caves that the reservoir earthquake lead to in the carbonate distribution area can cause the deformation and destruction of the bank landslide and the sudden disappearance of surface water sources,which affect the lives of local residents and social production activities.This paper selects 1610 data in total of earthquakes greater than 1.0 that occurred from June 2003 to December 2020 as the research samples.Through the Regional Geological Survey and organized the data of the reservoir already existing,and the tectonic geological analysis method adopted,analyze the laws of migration,the periodicity of time and the genetic mechanism of the microseismic group.using Statistical Forecasting Model predict the trend of reservoir earthquakes in the study area.It is considered that:(1)From the space point of view,the reservoir earthquake has a certain migration law:the triggered reservoir earthquakes controlled by the Jiuwanxi fault have the characteristics of gradually migration to the south.The triggered reservoir earthquakes controlled by the Xiannüshan fault are limited to the northern extension of this fault.The induced reservoir earthquakes on the west side of this fault(near Zhouping Town)has gradually migration to the south.The triggered reservoir earthquakes jointly controlled by the Gaoqiao fault and Niukou fault have the characteristics of migration to the south at first and then to the east nearby the Niukou Town.The induced reservoir earthquakes distributed between the Niukou fault and Shuitianba fault have the characteristics of migration to the north and then these become disappearred.The induced reservoir earthquakes distributed on the hanging wall of the Gaoqiao fault gradually migrated to the south.(2)From the time point of view,the reservoir earthquakes have obxiously periodicity.It is periodicity of long period that mainly relate to the reservoir water level.And it is divided into three periods,which correspond to the water level of 135,156 and 175 respectively.The periodicity of short period relate to the rapid fluctuation of the reservoir water level.(3)Through the collection and analysis of the focal mechanism in the study area,the calculation of b-values and the Regional Geological Survey conclude that the "triggered" and "induced" reservoir earthquakes in the study area and get different genetic mechanisms.The "triggered" reservoir earthquakes are mainly related to the large fault belts in the study area:Jiuwanxi fault is steep at first and then slow down so that this is wider seismic expansion.Xiannüshani fault is steeper always so that this is narrower seismic expansion.Niukou fault and Gaoqiao fault are mainly concentrated on the center of these two fault zones;the "induced" reservoir earthquakes are mainly related to the collapse of caves and mines based on the field investigation about soil cave and spring water flow.(4)This paper will use Statistical Forecasting Method to select different factors of induced earthquakes,its condition and Prior Probability of earthquake.Then we can use Statistical Forecasting Model for the study area.The results show that near the end of the northern extension of the Xiannüshan fault,the contact area between the Gaoqiao fault and the Niukou fault and the Longchuan River on the west of Gaoqiao fault are belong to the strength reservoir earthquakes area;Other places of along the Jiuwanxi fault zone,between the Gaoqiao-Niukou fault and near the fault to the west of the Gaoqiao fault are belong to the medium-strength reservoir earthquakes area;The karst cave development area of west of the Xiannüshan fault,the west Gaoqiao fault and the mine cave development area that is between the Niukou-Shuitianba fault zone are belong to the weak reservoir earthquakes area;The rest of the study area aree belong to the microseismic area.