Coseismic Model Inversion Of Yangbi Earthquake Considering The Distance Weight Of InSAR Deformation Observation Data

In recent years,with the development of spaceborne synthetic aperture radar interferometry(In SAR)and the continuous upgrading of various radar systems,the advantages of large-scale monitoring and high spatial resolution imaging make it widely used in seismic deformation acquisition and seismic source parameter inversion.However,when using In SAR deformation field for source parameter inversion,if using SAR image data from the same satellite platform,most of the existing studies believe that the accuracy of observation points is the same and give the same weight to the whole deformation field.In fact,due to the different influence of vegetation cover,atmospheric effect and other factors,each observation point has different accuracy due to different degree of decorrelation,Therefore,it is unreasonable to directly give the same weight to the whole deformation field in source parameter inversion.In view of this problem,this paper believes that the closer the observation point is to the fault,the greater the deformation magnitude and the higher the signal-to-noise ratio.Therefore,the correlation research of source parameter inversion considering the distance weight of In SAR deformation observation data is carried out,and the simulation experiment proves its reliability under different noise levels and different degrees of decorrelation.Finally,the Yangbi earthquake on May 21,2021 is taken as the research object,The established inversion model combined with distance weight is used for fault slip inversion.Firstly,according to the fact that when the earthquake occurs,the closer the fault is,the greater the surface shape variable level is,and the higher the signal-to-noise ratio of the observation point is,this paper proposes to take the reciprocal of the distance between the observation value and the fault as the weight of each observation value,and establish the inversion optimization model.Two kinds of simulation experiments are used to verify the reliability of the model.Simulation Experiment 1 is mainly aimed at the applicability of the model under different levels of noise.The results show that the sliding distribution obtained by the model is more accurate,and the sliding distribution accuracy of three different types of faults is improved by more than 21%.Simulation Experiment 2 is aimed at the reliability of the model under different degrees of decorrelation.The results show that when the deformation in Los direction is more than 16% involved in the inversion,reliable results can be obtained,and the inversion accuracy of the model is improved by more than 11%.In this paper,Sentinel-1A ascending and descending wide-range SAR image data are used to obtain the ascending and descending coseismic deformation field of Yangbi earthquake based on the D-In SAR two track method.The comparison shows that the descending deformation field has high quality and is distributed in a flat elliptical symmetry,and the long axis is NW-SE direction.The comparison of ascending and descending coseismic deformation field shows that the motion trend of the two plates is opposite,indicating that the earthquake is dominated by strike slip.Among them,the maximum shape variable of the west wall of the ascending track is about 5.6 cm,the maximum shape variable of the east wall is about – 6 cm,the maximum shape variable of the west wall of the descending track is about-6.4 cm,and the maximum shape variable of the east wall is about 8cm.The coseismic deformation field is continuously distributed,indicating that the seismic fault has not broken to the surface.In order to further analyze the fault structure and seismogenic mechanism of Yangbi earthquake,this paper takes the observation data of coseismic deformation field obtained by In SAR technology as constraints,and carries out the inversion of fault geometric parameters and slip distribution in combination with the distance weight of each observation value.Firstly,the fault model published by USGS is set as the initial fault model,and the optimal solution of geometric parameters is obtained through optimization: the fault is 27 km long,16 km wide,the dip angle is 83.5°,the strike angle is 135.8°,the longitude and latitude of the upper left corner of the fault is 25.7 E,99.8 N,and then the fault is classified as 1×1km is discretized into 432 rectangular elements,and the fine slip distribution of each sub fault is obtained by inversion.From the fault slip distribution obtained by inversion,it can be seen that the Yangxi earthquake is mainly dextral strike slip,the slip center is located at the underground depth of about 5-7 km,and its maximum slip is 0.57 m.Comparing the inversion results without combined distance weight with the inversion results combined with distance weight,adding distance weight can indeed improve the inversion accuracy to a certain extent,the closer to the fault,the higher the accuracy.