Study On The Activity Of Bangda Fault In Eastern Tibet And Its Engineering Significance

Bangda fault is located in the eastern part of the Qinghai-Tibet Plateau,adjacent to the boundary between the Eurasian plate and the Indian plate.It belongs to the eastern segment of the eastern boundary fault of the translithospheric fault—Bangong Lake-Nujiang River ophiolite belt.Its unique geotectonic location and intricate regional geological background have resulted in the structural pattern of the development of active faults,frequent seismicity,frequent occurrence of adverse geological phenomena and poor stability of the regional crust.Therefore,it is very important to investigate and study the characteristics of Bangda fault activity and to determine its activity,and it has important guiding significance for how to select the suitable surrounding engineering planning site area for stability evaluation.In this paper,field geological survey,combined with comprehensive technical methods and means such as seismic geological interpretation,remote sensing geological interpretation,intragranular microstructural study,active fault dating,geophysical analysis and fuzzy mathematics calculation,the characteristics of tectonic activities in the control range of Bangda fault are studied in depth,especially since the late Quaternary,and the newly proposed engineering area is also studied.Preliminary evaluation of construction adaptability is made.Bangda fault is located at the turning point of the eastern boundary fault of Bangong Lake-Nujiang River suture zone toward the Northeast uplift.The plate compression and collision lead to the lateral escape of deep material.The surface is not only reflected in the change of the river and mountain strike,but also in the structural transformation,resulting in the motion properties of the Bangda fracture to be phased and different in time scale and spatial position.In the end of Mesozoic era,with the gradual closure and extinction of the Nujiang Tethys oceanic basin,the area was transferred to the intracontinental convergence and the plateau was uplifted.the main mode of fault movement was that the melange formation in the south-west conjunction zone thrusted over the clastic rock formation in the north-east side,while in the neoid,the fault showed the movement characteristics of right-lateral strike-slip in the horizontal direction.The study area belongs to the eastern part of the Tethys tectonic domain.Large-scale active faults and strong seismic activities are widely developed in the region.The oblique faults of Guoqing-Xieba and Semuxiong faults,on the one hand,cause the segmentation of the Bangda fault in strike,on the other hand,absorb and transmit the kinetic energy released by the faults,which limits the activity of the middle part of the Bangda fault.Through comparative analysis of the same fault and different sections of the same fault in terms of topography,geomorphology,Quaternary tectonic geology and chronology,it is determined that the middle section of the Bangda fault has been in a relatively stable state since the late Quaternary.At the same time,through the in-depth study of the activity characteristics of the Bangda fault,the preliminary analysis of the engineering geological environment in the newly constructed engineering area near the fault,based on the comprehensive analysis results of topography,physical and geological phenomena,hydrogeological structure,rock mass quality of chamber and structural stability,it is considered that the new proposed engineering area is suitable for construction.