Main Seismic Structure Characteristics And Seismicity Analysis Of Huoshan Area In Anhui Province

Anhui Huoshan area is a “window” reflecting the change of the earthquake in East China.However,there is less researches on the characteristics of Neotectonic movement and seismic activity around this area.On the basis of summarizing previous researches,this thesis combines field geological survey,remote sensing interpretation,tectonic stress field inversion and statistical principle to study and analysis the characteristics of the earthquake-control faults and their activity,the characteristics of modern tectonic stress fields and seismic activity.The thesis show results as follow: 1.There are three earthquake-control faults in the study area,which are Luoerling-Xiafuqiao fault with NE trending,the Meishan-Longhekou fault with NW trending and the Qingshan-Mozitan fault NW trending,respectively.Among the three fault,the Luoerling-Xiafuqiao fault has the highest activity intensity,along which the seismic activity is the most frequent.The active nature of the Luoerling-Xiafuqiao fault is mainly normal fault and right-lateral strike-slip.The latest activity era of the Luoerling-Xiafuqiao fault is the early of late Pleistocene;the Meishan-Longhekou fault zone develop much branch fracture,with the normal and left-lateral strike-slips.The fracture activities are mostly concentrated at the intersection with the NE-trending faults.The most recent activity of the Meishan-Longhekou fault is the early of late Pleistocene;the Qingshan-Mozitan fault formed in the Cretaceous period.Since the late of Middle Pleistocene,there has been some activity and the nature of motion is normal faults.2.there have experienced at least two stage tectonic stress fields in the study area: early stage is in the early Cretaceous-late Cretaceous;late stage is in Paleogene.In early stage,the modern tectonic stress field show the northwest-southeast near horizontal extension and vertical extrusion,with the maximum principal stress axis dip angle 60°~80°.In late stage,the modern tectonic stress field show almost east-west diagonal extrusion and near-south-north horizontal extension,with the maximum principal stress axis dip angle 30°~40°.On the whole,it is characteristic of the modern tectonic stress field of Huoshan area that the extension changes clockwise,and the extrusion gradually shifts from oblique to near horizontal.3.the level of seismic activity in the study area is below average and currently in a relatively quiet period of the IV cycle of activity.Earthquakes are most likely to occur on the eastern side of the Luoerling-Xiafuqiao fault and its intersection with the northwest fault.According to the recurrence period of moderate earthquake with 100-150 years,the time law of the relatively quiet period gradually shortens and seismic zone formed in the area,there is a possibility that the area will enter a relatively active period in the long-term or ultra-long-term future and strong earthquake will occur in the Huoshan area.