Measurement Of Typical Co-seismic Displacement Of Maduo M7.4 Earthquake Based On Surface Rupture Deformation Analysis

Coseismic displacement and its distribution are important quantitative parameters for understanding rupture mechanism and surface rupture process.They are of great significance for analyzing fault activity mechanism,potential seismic risk and determining the safety distance.For the strike slip seismic surface rupture zone with dip slip component,its coseismic displacement consists of three parts:coseismic strike slip displacement,horizontal component of coseismic dip slip displacement(tension or shortening)and vertical component of coseismic dip slip displacement.The lack of a component will inevitably lead to the deviation in the study of rupture zone.The coseismic displacement of the surface rupture zone in traditional earthquakes mainly depends on linear benchmarks across the rupture zone,but it is difficult to obtain the coseismic displacement by using this method when the surface lacks linear benchmarks.A M7.4 earthquake occurred in Maduo,Qinghai,on May 22,2022.The seismogenenic fault produced a 160-km-long surface rupture,which is the largest earthquake in China after the 2008 Wenchuan Ms8.0 Earthquake.Post-earthquake investigation and later processing and analysis of UAV image measurement data determined the geometric of the Maduo earthquake surface rupture zone and its kinematic characteristics.However,the Maduo earthquake fracture zone is distributed in grasslands,wetlands and bare barren beaches,with small topographic relief,few human activities,few linear features,and lack of measurement marks.It is not easy to obtain the deformation parameters of the fracture zone by traditional measurement methods.Satellite geodesy can obtain large-scale coseismic deformation field,but the deformation of inner high-strain zone may lead to loss of coherence,so it is impossible to obtain the deformation field and deformation details of inner high-strain zone of surface rupture.The aerial photogrammetry technology of UAV with differential positioning is a high-precision and efficiency field mapping technology rising in recent years.It has been widely used in the field investigation and measurement of large earthquakes.Based on Unmanned Aerial Vehicle(UAV),the Langma Gaheri section and the Yematan section with dip-slip component are selected.Based on the detailed analysis of the rupture and deformation characteristics in the fracture zone,the measurement marks and methods of coseismic strike slip displacement and dip slip displacement are determined,and the coseismic displacement is measured and calculated.The main conclusions are as follows:(1)Structural combination characteristics of seismic surface fracture zone.In the direction of vertical fracture zone strike,the seismic surface fracture zone can be divided into two parts:inner high-strain rupture zone and outer rupture zone.The seismic fracture density in the inner high-strain rupture zone is high,and the tensile shear fracture,shear fracture and compressive fracture are developed;The outer rupture zone has low seismic fracture density and mainly develops tensile fractures.(2)The difference of deformation characteristics between inner and outer zones.The deformation of the outer rupture zone is weak,and a single rupture shows pen linearity.Combined with previous studies,it is interpreted as the seismic rupture F0 without rotational deformation;The inner high-strain rupture zone has strong deformation,and there are a large number of rotational compressed turf blocks.The initial strike of the turf block boundary rupture F1 is consistent with the non-rotational seismic crack strike of the outer rupture zone.The rotation deformation of turf block was observed in the field investigation and indoor deformation detail analysis,which is consistent with previous studies.Therefore,we use the rotating turf block in the inner high-strain rupture zone as the displacement measurement mark to obtain the coseismic strike slip displacement.(3)Measurement and calculation of coseismic strike slip and dip slip displacement.Based on the rotation deformation of the turf block,the typical displacement points were selected,and a total of 34 coseismic strike slip and dip slip displacements of the Langma Giaheri section and Yematan section in the study area were obtained.The vertical components of the dip slip displacement in the Langma Giaheri section are relatively stable,all around 0.5m;the horizontal component of dip slip displacement is characterized by large in the middle and small on both sides,and the maximum tension is 3.35m;the strike slip displacement gradually decreases from west to east of the fracture zone,and the maximum strike slip displacement is 2.59m.The vertical component of the dip slip displacement in Yematan section is relatively stable,about 0.5m,and the horizontal compression amount of the dip slip displacement is between 0-0.5m.The strike slip position gradually increases from west to East,and the maximum strike slip displacement is 2.76m.For the strike slip seismic surface fracture zone,when there is an obvious intersection angle between the strike of the fracture zone and the direction of the maximum principal compressive stress,a positive(reverse)dip slip component may occur.(4)The deformation process of the seismic surface rupture zone in the study area can be divided into three stages:the development of oblique seismic rupture in the innner and outer zone,the formation of turf blocks in the inner high-strain zone and the rotation deformation of turf blocks.(5)The total deformation of strike slip earthquake surface fracture zone includes distributed deformation and surface fracture zone deformation,and the surface fracture zone deformation can be divided into inner zone deformation and outer zone deformation.In this paper,through the calculation of turf block rotation deformation,it is found that the displacement is the main deformation displacement of the inner high-strain rupture zone,and part of the deformation is located in the outer rupture zone and the distributed zone.