Comprehensive Geological Evaluation Of CEPC Site Selection Area

The Circular Electron Positron Collider(CEPC)is a large-scale particle collider advocated by China's high-energy physics community and facing the future.The major scientific device applied to high-energy physics research puts forward high-standard geological conditions for the site."Site selection and geological suitability" is an innovative achievement proposed by the Institute of Geology and Geophysics,Chinese Academy of Sciences in the process of site selection for major scientific projects.It combines geological multi-factor impact analysis and multi-method comprehensive survey as well as providing a basis for site selection and scheme selection of major projects.The CEPC Changchun site selection area takes the southern part of Changchun City,Jilin Province as the pre-selection area.Because this major scientific device involving high-energy physics has high requirements for the site selection area for geological conditions,this article is based on the principle of "major engineering site selection and geological suitability",the geological suitability of the site selection area in Changchun is discussed in depth.The use of remote sensing,geographic information system,geophysics and other methods to carry out comprehensive geological evaluation of the study area,mainly achieved the following results and understanding:(1)The thesis realizes the semi-automatic recognition of linear structures based on remote sensing images: The Gram-Schmidt method is used to fuse Landsat OLI imageswith domestic GF-2 images to obtain 10 m resolution images,which increases the recognizability of linear structures.In the LINE module of the PCI Geomatica software,the edge detection is performed using the Canny operator,and then edge connection and linear interference removal are performed to realize the semi-automatic recognition of linear structure.In the study area,four large faults including the east and west branches of the Yilan-Yitong fault,the Dongliaohe fault,and the Siping-Dehui fault,as well as 19 main linear traces and Several small linear traces.(2)The regional structural stability was comprehensively explored through fault activity,earthquake and its safety,and regional tectonic stress field: the Yilan-Yitong fault is dominated by right-handed strike-slip,with a small vertical motion component;After two stretching-extrusion processes,two main high-angle thrust faults were formed.The south-east main faults tended to be south-east or nearly upright,and the north-west main faults tended to north-west;the Dongliaohe fault was the edge-slip of the Yitong basin.According to the linear structure semi-automatic recognition method based on remote sensing images,there are 19 main linear structures,mostly NW strikes,approximately parallel to the Dongliaohe fault;a few linear structures are NE strikes,approximately parallel to the Yilan-Yitong fault.According to geological monitoring data,the maximum peak acceleration of ground motion in the study area is 0.05 g and0.1g.The occurrence of the earthquake may be related to the activity of tectonic faults.The seismic activity is not strong today.The direction of the axis of the maximum principal compressive stress is now near the north-south direction.(3)Through the analysis of regional crustal and gravity characteristics,combined with the three-dimensional geological model of the study area,the thesis discusses the crustal stability of the study area: the crustal thickness of the study area is between 32 ~33Km,the geothermal gradient is low,the crustal structure is stable.The gravity anomaly in the site selection area is relatively stable,the composition of reactive materials is relatively stable,and there is no obvious mutation of gravity anomaly,so the regional structure is not developed;the three-dimensional model is established using the GOCAD software and the Grav3 D three-dimensional gravity inversion software.Thethree-dimensional geological model of the site area can more clearly reflect the underground geological conditions of the site area and provide a basis for the comprehensive geological evaluation of the site area.(3)The thesis selects 10 index layers of five major element layers,including surface stability,structural stability,crustal stability,hydrogeological conditions,and traffic conditions in the study area.Using analytic hierarchy process,Matlab software is used to calculate the weight of each index element.It was used to obtain comprehensive geological evaluation map of the study area.The results show that the unstable and less stable areas in the study area are mainly distributed along the faults,and the more stable and stable areas are mainly distributed in the south of the study area.Among them,the CEPC site is basically in the stable area,and the terrain is not undulating and the structure is stable The external dynamic geological phenomenon is relatively undeveloped,the rock mass is hard,the thickness of the Quaternary overburden is small,and the communication conditions between groundwater and surface water are poor,making it an ideal site for major scientific installations.