The Active Evaluation And Area Stress Field Analysis Based On The North Rim Of Western Qingling-Baoji To Tianshui Section

In recent years, the research on active faults has got more attention with the need of earthquake prediction and engineering construction。The Bao ji city,which located in the north-south seismic, although mid-strong earthquake seldom happened there, but it has the tectonic background of breeding an earthquake。The northern fracture of western Qingling lays on the west end of Baoji is one of the most grand scale tectonic belt which traverses the middle part of our country, in order to evaluate the activity of the fracture accurately and its influence on Baoji city, we launched the research on the fault zone in depth which based on the project——《The active fault detection and the earthquake risk analysis of Baoji city》。Firstly, we discovered the distribution characteristic of Baoji-Tianshui fracture which belong to the north fracture of western Qingling, the north fracture of western Qingling has the reflection of thrust character overal:the Baoji-Tianshui section east start from the Zhaoyu village, west to the Pingtao, Xizhuang village, Xinmin village, south of Chisha town; Tongdong village to north of Tuoshi town, across the Wei river, the overall length is 41kilomitres, the tendency is north, the inclination is 35°-57°, move toward 290°;along the fault zone, Yakou landform is obvious, geological disaster is breeding。Secondly, through the exploring of trench that across the fault and cleaning of outcrops, still the geomorphic survey work, we launched the work of identifying the activity of the fault, ensuring that the last activity of the fault zone took place during the early MedioPeistocene, after that, there is no obvious' activity any more。Thirdly, through the area stress field study we can conclude that the Baoji-Tianshui section fracture of Western Qingling north fracture is the northeast border of early Qinghai-tibet plateau, after the quaternary, with the northeast expansion effect of Qinghai-tibet plateau, it has become the part of the Qinghai-tibet plateau uplift body, its activity is becoming gradually weak。At last, with the field investigation result, the area stress field and the tectonic environment research we can conclude that there are three key areas which breeding the seismic condition of Baoji area:the Long county-Mazhao fracture intersection with the south rim of Qingling section; the Long county-Mazhao fracture intersection with the Wei river fracture section; the Zhaoyu-Xiashi ditch that lays to the west of Baoji section.The whole research has reference value to the seismic zonation and disaster-resistance of Baoji city.