Study On Structural Stability Of Jinkouhe Area In Sichuan Province

Jinkouhe area is located at the junction of Leshan city,Meishan city,Ya'an city and Liangshan prefecture in Sichuan province.It belongs to the transitional zone between the southwest edge of Sichuan Basin and the east edge of Qinghai-Tibet Plateau.The neotectonic movement is active,and the fold and uplift are strong,and the complex geological environment conditions restrict the local economic construction activities.Therefore,it is of great practical significance to study the structural stability in this area.In this paper,the characteristics of regional geological structure and the temporal and spatial distribution of seismic activity are comprehensively analyzed.Through detailed field investigation,the development of stratum rock and fault structure in the study area is found out.The area crosses two first-class geotectonic units of Qiangtang-Sanjiang orogenic system and Yangtze continental block,with violent tectonic movement,forming several active fault zones,including the NE Longmenshan fault zone,the NW Xianshuihe fault zone and the NW Yingjing-Mabian-Yanjin fault zone,the NS Anninghe fault zone and the NS Daliangshan fault zone.The seismic record data shows that the distribution of regional seismicity has certain regularity,which is obviously controlled by the faults in the region.Almost all strong earthquakes and above are distributed along the active fault zone,and most of the medium and small earthquakes are also concentrated around the regional faults,with obvious linear and cluster distribution characteristics.Three groups of faults are developed in the study area,which are NE,NW and nearly NS.The faults are mainly thrust faults with weak activity.The field geological and geomorphological investigation and dating experiments show the latest activity age of these faults is concentrated in the early-middle Pleistocene.In the evaluation of structural stability in the study area,the weight of evaluation factors is obtained by using AHP,and the quantitative evaluation of structural stability is carried out by using fuzzy comprehensive evaluation model and GIS software,and the single factor zoning map and comprehensive zoning map of structural stability are drawn.The results show that the structural stability grade of the study area is mainly sub stable(II)(69.1%),followed by stable(I)(30.9%);the crustal structure,deep faults,earthquake distribution and maximum magnitude of the evaluation factors are more sensitive to the structural stability of the study area.It also proves that it is feasible to use AHP to determine the weight of evaluation factors.This method can adapt to the evaluation of structural stability under different geological conditions and avoid simply applying the weight determination experience of other regions.The membership degree of fuzzy comprehensive evaluation model also makes the quantitative evaluation of structural stability possible.It can realize the transformation from qualitative to quantitative through membership degree.Combined with GIS software,it can accurately depict small areas with different structural stability evaluation grades.