A Study On Active Faults And Crustal Stability In Qingjiang River Basin

In the west of Hubei , Qingjiang River basin is one of important hydropowerenergy sources in our country. The crustal stability of river basin and damsites isbasic research for hydroelectric station construction. From the mechanical essenceof crustal stability, the evolutional features of regional fault activity and tectonicstress field in three dimensional space are analysed in this thesis. Then, the assess-ment of crustal stability for deep geological masses and surface rock masses as wellas damsites area are carried out separately by combing three dimensional tectonicstress field, deformation field and energy field to three dimensional space. The ba-sic ways and method used for three dimensional assessment of crustal stability areproposed. In summary, the following conclusions can be drawn:①Regional crustal structure is that of stable platform margin type, and it canbe divided into three layers composed of upper crust and middle crust as well aslower crust. Deep state of gravitation gradient belt stands for slope belt of M surfaceslight tilting form E to W, and it doesn't result from deep fault;②The main fault activity in Qingjiang River basin gradually become weakersince they formed during Yanshanian movement. As a result, the degree of crustalstability become higher;③The inverse rusult of tectonic stress fields shows that the maximum com-pressional stress axis is S—N and NW direction during Yanshanian movement, andNE direction during early Himalayan orogeny, as well as NNE direction duringneotectionic period in Qingjing River basin, meanwhile, the magnitude of tectonicstress field get smaller;④The result of three dimensional numerical simulation of present tectonic fieldshows that the character of present tectonic stress field is controlled by regional tec-tonic frame, and the maximum compressional stress axis is NNE or S—N directionwith division ;⑤The character of present tectonic movement and tectonic stress field inher-ited that of neotectonic movement, and earthquake activity is controlled by NNW and NE—NNE direction faults compressed with present maximum stress.⑥Based on segmentation of geometric and deformation structure, it is effec-tive method that fracturing segmentation of fault has been carried out combiningwith earthquake , geodetic measurement, fractal dimension etc. , It′s result help todefine earthquake active parameter and elevate the reliability of assessemnt ofcrustal stability.⑦It is a new idea that three dimensional assessment of crustal stability is car-ried out based on synthetic study of three dimensional crustal structure, tectonicstress field, deformation field, energy field and earthquake activity etc.⑧The result of assement shows that most of Qingjiang River basin is stable,the regions where deep and surface geological masses are substable or relative unsta-ble are the whole part of Xiannushan fault, the whole part of Qingjiang fault andYujiang fault as well as Xianfeng fault. The stability of rock and soil masses onsurface corelates with that of deep geological mass. All of damsite area of hy-dropower project are located in stable region.