Studies On The Late Quaternary Tectonic Deformation Of The Xigeda Fault

As one of the most seismically active areas in mainland China,the SichuanYunnan block has a complex structure and strong seismic activity,and there are many large-scale Holocene active faults distributed in the area,which has the tectonic conditions for strong earthquakes.The Xigeda Fault zone is also a deep and large fault as an important boundary fault within the secondary block.The research on active structures is of great significance for evaluating the seismic risk of the region.Based on the traditional and mature theory of active tectonic research,this paper uses remote sensing image interpretation,field geological and tectonic landform surveys to study the late Quaternary activity characteristics and paleo-earthquake activity history of the fault.The following conclusions are obtained:(1)The total length of the Xigeda active Fault is more than 150 km,and the overall strike is close to SN.Along the fault line,many basins are controlled and developed.In Xinjiu Village,it extends northward and is divided into two branches,east and west,and the activity of the west branch is weak.Since the late Quaternary,the fault has been dominated by strike-slip movement,but its cross-sectional tendency is different along the strike.According to the change of the fault geometry along the strike(such as strike transition and geometric discontinuity),the Xigeda Fault is divided into 4 segments:North Section(East Branch)Heilongtang-Puwei Town Section,inclined to W;Middle Section(East Branch)Puwei Town-Xigeda Village Section,inclined to W;South Section(East Branch)Xigeda Village-Jiangbian Township Section,It tends to E;the West Branch tends to W,and there is a certain pivot.(2)According to the results of the field geological and geomorphological investigation,the geological bodies and geomorphological feature points along the fault line that were broken off were selected,and the displacement measurement and geomorphological feature points were carried out using the high-precision photogrammetry of unmanned aerial vehicles,optical luminescence,and carbon 14 dating techniques.Dating work,combined with previous research and analysis,the slip rates of each segment have been obtained: the horizontal slip rate of the northern segment(eastern branch)since the Holocene is about 2.8 mm/a;It is 1.1-1.6 mm/a,the horizontal slip rate is about 1.5-2.1 mm/a,and the vertical slip rate is about 0.3-0.5mm/a since the early Holocene;The rate is about 1.7mm/a;the horizontal slip rate of the western branch of the fault since the Late Pleistocene is about 1.7mm/a.(3)Three paleo-seismic events were obtained through the excavation of Dushu Village,Zhonggangou and Dalong Village: Event 1,limited to the age of 30890±170a BP;Event 2,The limited age is 5990±30a BP-1530±30a BP;for event 3,the limited age is 390 a BP-250 a BP.(4)Through the above work,according to the calculation method for calculating the average recurrence period of paleo-seismic,the average recurrence period of the eastern branch of the Xigeda Fault is 14.45-17.17 ka,and the elapsed time of the last event is about 300 a BP;according to the length of the active fault or the earthquake surface The statistical relationship between the length of the rupture zone(L)and the magnitude(M),the potential maximum earthquake magnitude of each sub-section of the eastern branch of the Xigeda Fault is obtained: the northern section(eastern branch)is M7.1,the middle section(eastern branch)is M7.3,the southern section(east branch)is M7.2.