Present Three-dimensional Crustal Movement And Stress Field Around The Dabie Mountains And Surrounding Area

The study area,across the North China block,the Yangtze block and the Dabie orogenic belt,is experiencing a complex tectonic evolution.Specifically,the Tanlu fault zone with shear motion crosses our study region in NE trending,which is the developed area with large population and perfect infrastructures.Invaluable loss will be caused if a strong earthquake occurs.Since the Tanlu fault zone was found,the geologists had made lots of researches on the structural evolution of the fault from different aspects.However,there is a debate about the different activity between the middle and the southern segments.The dynamic background of the Tanlu fault zone is also still in dispute.Our research combines the regional crustal deformation with the tectonic stress to explore the issue of crustal motion of the Tanlu fault since the new tectonic period and its geodynamic mechanism.By using the linear dynamic method,the long-term scale of vertical movement across our study region is inferred from the leveling data.By using GAMIT/GLOBK software,the horizontal movement with respect to stable Eurasian is derived from GPS data.The characteristics of the crustal movement is analyzed based on the three-dimensional crustal movement field.(1)Generally speaking,the amplitudes of uplift and subsidence are small,but the regional difference is significant.The uplift movement of the Dabie Mountains is weak,and its east side uplifts slower than the west side.Thesubsidences across the Huaihe river plain and Yangtze river delta are very obviously,this may be caused by groundwater withdrawing.The Sunan region is uplift generally.Combining with the existence of abnormal low velocity zone inferrd from Pn wave,our result suggests that the crust of this region is weak and it is apt to be deformed by extrusion.(2)According to the horizontal motion relative to the Eurasian,this region moves southeastward.In general,the overall differential horizontal movement is very small.The crustal deformation in this area is unsignificant derived from the three-dimensional crustal movement.Then we make a comprehensive analysis combing the three-dimensional crustal movement field with the tectonic stress field.The regional tectonic stress field result suggests that the horizontal maximum principal compressive stress is in the direction of NEE-NE.But the stress state has significant difference.Combining with the tectonic characteristics of the stress state,the study area is divided into three regions,the west of the Tanlu fault zone,the Subei basin and the Sunan uplift zone.The horizontal maximum principal compressive stress of the west of the Tanlu fault zone shows circular radial distribution which is consistent with the distribution of the lateral extrusion produced by the uplift of the Tibetan Plateau.According to the previous results,three-dimensional crustal movement and the structural stress field,we analyze the reasons why the direct evidence of activity has not been found in the south of the Tanlu fault zone since the late Quaternary.The volcano formed during the Quaternary in Jiashan region behaves as a barrier between the middle and the southern segments of the Tanlu fault,zone,and the southern Tanlu fault is restricted by the end effect of the fault.The southern fault zone with NEE trending is cut into several sections by the NWW trending fault,its activity is weak.Meanwihle,the right-lateral NE trending fault and the left-lateral NW trending fault extruded by the NEE compressive stress coincindes in the Coulomb-Anderson model,suggestingthat it is not easy to produce a large strike slip fault.