Research On The Seismic Activity History Of Faults In The Northern Margin Of Qinling Mountains Based On Structural Geomorphological Features

The fault on the northern margin of the Qinling Mountains is the boundary fault of the Fenwei seismic zone in our country,and has the potential to cause earthquakes of magnitude 7.5 or higher.Due to the limitation of technical methods and natural conditions,the history of strong earthquake activity of the fault since the Late Quaternary has not been studied in detail.In particular,human engineering activities along the fault have intensified in recent years,making it difficult to obtain quantitative parameters of the fault's activity using traditional seismic geology methods.The existing results mostly qualitatively or semi-quantitatively explore the activity of the fault on the northern margin of the Qinling Mountains,especially the lack of detailed research on the quantitative activity parameters such as the paleoearthquake sequence of the northern Qinling fault,the earthquake recurrence period,etc.,which directly restricts its earthquakes.The scientific understanding of hazards also affects the risk assessment of strong earthquake disasters in the Guanzhong area.Based on previous studies on the segmentation of faults in the northern margin of the Qinling Mountains,this paper selects the most active middle section of the faults in the northern margin of the Qinling Mountains as the study area(Mei County?Lantian County),and uses the ZY-3 satellite stereo image pair to make the resolution It is a digital elevation model(DEM)with an accuracy of 1.5m and 5m.Use River Tool 3.0 water system software to extract the longitudinal profile of the river system in the DEM study area,identify the location of the river knickpoint by analyzing the elevation and slope changes of the longitudinal profile,and combine the stratum lithology,the characteristics of the river course,the confluence of tributaries and other characteristics to filter Out of the structural river knickpoint.Using the corresponding relationship between the tectonic origin knickpoint sequence and the paleo-seismic event,using the most recent seismic activity(1000a BC)as a ruler,calculate the retreat rate of the latest first-level river knickpoint in each gully,and then calculate the next new level The time of formation of the knickpoint and the third-level knickpoint is 5624?7425a,8432?10691a,and finally the time of three paleo-seismic events(3000a,5624?7425a,8432?10691a)in the northern margin of the Qinling Mountains is inferred.The recurrence interval of strong earthquakes on the northern margin of the fault is 2800-4400 years.The average height of structural fractures can be regarded as the seismic co-seismic displacement.According to the empirical relationship between the normal fault co-seismic displacement(L)and the seismic moment magnitude(M_W),the earthquake that induced the formation of structural fractures is calculated The magnitude of the magnitude is 7.65±0.02.In addition,this thesis also takes the ancient landslide clusters in the north piedmont of Qinling as the research object.Through high-precision DEM and high-resolution multispectral remote sensing images,the ancient landslide area in the north piedmont of Qinling is interpreted in detail,and the calculation is calculated.For the area of each ancient landslide,using the distribution characteristics of the landslide,the magnitude of the earthquake that induced the ancient landslide group at the northern foot of the Qinling Mountains was calculated to be 7.6 to 8.1.At the same time,two large-scale landslides in Cuihua Ganqiu Pool and Shuiqiu Pool were dated by in situ cosmogenic nuclide dating,and the occurrence times of the two landslides were8.8±0.7ka and 8.6±0.3ka,respectively.Finally,comparing the results obtained by two independent research methods of river knickpoint sequence and ancient landslide distribution characteristics,it is found that on the time scale,the ages of the two landslides in Ganqiuchi and Shuiqiuchi are(8.8±0.7ka?8.6±0.3ka).It is in good agreement with the time of the third to last paleo-earthquake(8432?10691a)induced by the fault in the northern margin of the Qinling Mountains.On the spatial scale,the earthquake magnitude(7.85±0.25)that induced the ancient landslide was calculated by using the distribution characteristics of the belt-shaped landslide at the northern foot of the Qinling Mountains,which is basically the same as the magnitude calculated by using the height of the tectonic fracture point steep ridge(7.65±0.02).According to the comparison results on the above-mentioned time-space scale,it is believed that the formation of the ancient landslide group at the northern foot of the Qinling Mountains has a strong correlation with seismic activity.This research provides quantitative data support for the time-spatial response relationship between the formation of landslides on the northern margin of Qinling Mountains and seismic activity.It is also important for comprehensive analysis of seismic recurrence models of faults on the northern margin of Qinling Mountains and to understand the seismic hazards of faults on the northern margin of Qinling Mountains.Realistic meaning.