The Characteristics Of Active Faults And Analysis Of Seismic Activity In BaoJi Area

Baoji region is located in the western end of the Weihe basin. located in the southwestern rim of the Ordos block, located in the transition area of the middle and north section of the famous north-south seismic belt, a number of active faults through this area. It is also the transition zone of the East-West and South- North giant tectonic belt of chinses Mainland, the geological structure is very complicated. Although Baoji district are rare of mid-strong earthquakes in history, but it possesses structure condition of earthquake-gestating and earthquake-generating.This paper basis on the field geological survey, combined with predecessors' information, made a systematic study of the activities and characteristics of Baoji faults for the first time, and analyzed the tectonic stress field and seismic activity, the main results obtained are as follows:1,The main stratum exposed in this area are Archean-Early Proterozoic deep metamorphic rocks, middle-late Proterozoic clastic metamorphic rocks, Paleozoic clastic-carbonate rocks, clastic rocks of Mesozoic and Cenozoic loose sedimentary rocks and loess, etc., intrusive rocks are developed in the southern.2,The main landforms in Baoji region are block mountains, rift basins and the fault topography. the study area's northern is the Ordos Plateau, southern is the Qinling Mountains, central part is the Weihe River alluvial plain. General topography is characterized by north-south high, middle low, and showing a gradual decrease features from west to east. the formation and evolution of landforms by basement faults controlled. and the new tectonic movement has significant control to their formation role.3,The new tectonic movement are strong and complex, and there are a number of active faults in the area.1) The major active faults are West Qinling north margin fault, Weihe fault of Baoji section, Gaodian-Gaojia Village fault, the north margin fault Of Qinling, south margin fault of north Qinling, Yangjiawang-Huangniupu-Honghuapu fault, Liulin-Jia Village fault, Taoyuan-Guichuan Temple fault, Guguan-Guo town of fault, Qian Yang-Biaojiao fault, Longxian-Qishan-Mazhao fault.2) The field investigation found that Gaodian-Gaojia Village fault activity evidence of surface is not found, Weihe fault Baoji section are the buried fault, Liu Lin-Jia Village fault there is also not found surface evidence. Qian Yang-Biao jiao fault surface did not find fault outcrop, it should be buried fault.3) Since late Pleistocene there are two active faults:the northern margin fault of the Qinling, Longxian-Qishan-Ma zhao fault.4,Faults in the region is formed under the NEE～SWWto the compression, NNW～SSE to the tension stress, after the Collision of Indian plate with the Eurasian Plate.which 1) NW-trending faults formed in the Paleozoic, the late Early Pleistocene, by Sinistral strike-slip extrusion of eastern LiuPanshan. Counter clockwise rotation of the Ordos block, the expandable of north and south of Weihe fault basin, fault Sinistral strike-slip extension, dip-slip fault is formed.2) EW-trending faults formed in the Paleozoic. Mid-late Miocene, the northern margin of the Qinling fault, the Weihe River fault due to stress relaxation, from the pressure-shear tensional breaking into normal fault; Quaternary, West Qinling fault continue to be squeezed, the further development of reverse faults, while the northern marginal fault of the Qinling Mountains are still subject to east-west compressive stress, normal faults continue to develop, but its activities are uneven and intermittent inheritance characteristics.3) NE-trending faults formed of normal faults by the EW compression stress in the Mid-late Miocene, the obstruction of fracture due to rotation with right-lateral strike-slip characteristics in the late of the middle Pleistocene.5,Seismic activity are closed to active faults in Baoji area.1) Most of the earthquake region are concentrated in the North East, North West, East and West to the seismogenic structure of the compound and the area of earthquake control structures. North West trending fault has occurred in the history of many moderate and strong earthquakes, and earthquakes are more frequent.2) NE-trending fault zone activity is weak, there was only sporadic small earthquakes occur.3) In the southwest of the northern and southern structural belt, it is likely to occur more than 6 Ms earthquake in this area.