Inversion Of Coseismic Slip Distribution Based On Triangle Dislocation And Afterslip Of The Nepal M_W7.8 Earthquake In 2015

With the development of InSAR and GNSS technologies,using them to monitor the deformation of the surface caused by earthquakes,inverting the internal structure of the earth and dynamic processes play a very important role in revealing the mechanism of earthquake.This paper firstly based on the Nepal MW7.8 earthquake coseismic deformation obtained from 46 GPS stations and four different orbits of ALOS-2 and Sentinel-1A inverted the fault geometric parameters and coseismic slip distribution of this earthquake.The influence of the dislocation model,fault geometry and smooth constraint conditions to the coseismic slip distribution have been discuss.Then,based on the surface deformation field obtained from 32 continuous GPS stations in Nepal and three different orbits of Sentinel-1A/B in the past two years after the earthquake,the afterslip was inverted,and the viscosity relaxation effect was briefly discussed.The main work and achievements of this paper are as follows:(1)The Bayesian algorithm was used to invert the parameters of a single plane fault in the Nepal MW7.8 earthquake,and the coseismic slip distribution was inverted based on the triangular dislocation model.The results showed that the coseismic slip distribution of the MW7.8 earthquake extends about 140 km along the strike direction,at a depth of 8 km to 14 km,which the maximum slip is 6.32 m.The slip extends unilaterally from the epicenter to the southeast,and is basically parallel to the fault strike.Until the location of MW7.3 aftershock,it propagated to the north and southeast directions,forming a slip gap about 3m.(2)The coseismic slip distribution of the Nepal MW7.8 earthquake was inverted based on the rectangular dislocation model and compared with the coseismic slip distribution of triangular dislocation.The results show that the sliping characteristics of the two coseismic sliping distributions are consistent,but the triangular dislocation coseism ic sliping distribution shows more detailed sliping characteristics,the InSAR fitting residual is reduced?10cm,and the GPS fitting residual is reduced-2cm.(3)Using the ramp-flat-ramp fault structure proposed by Elliott et al.invert the coseismic slip distribution of the Nepal MW7.8 earthquake,the result is consistent with the slip distribution characteristics of a single plane fault inversion.Therefore,we believe that there may be both single and multi-segment fault structures near Kathmandu,which is consistent with the conclusion of Qiu Q et al.(4)The minimum moment regularization constraint was imposed on the Nepal MW7.8 earthquake.The result of coseismic slip distribution shows that it is located near a depth of 12.5 km and the slip has jumps and oscillations.The maximum slip is 8 m,compared with the results of most studies,the fitting residuals of coseismic surface displacements are larger.The maximum sliping and sliping characteristics obtained by using Laplace smoothing constraints are similar to most research results,and the coseismic surface displacement fitting residuals are smaller.Therefore,we recommend using Laplace smoothing constraints in this inversion of the sliping distribution.(5)Based on the PREM model,the study found that the post-earthquake displacement caused by viscous relaxation is generally smaller than the post-earthquake GPS displacement.The motion of model in the northern part of the earthquake area is the same as the GPS data.In the southern part of the earthquake area is opposite,so we believe that the viscous relaxation effect in the past two years after the earthquake has a small contribution to the post-earthquake deformation.The afterslip was inverted based on the surface deformation field obtained by GPS and InSAR after the earthquake.The results showed that the afterslip was mainly located at a depth of?25km,and the maximum slip is 0.35m.The released seismic moment is 5.5×1019N·m which is equivalent to a MW7.12 earthquake,accounts for about 10%of the coseismic released seismic moment.Afterslip mainly occurs in the downdip of the fault,and overlaps with a small amount of coseismic slip.At the same time,there is a small amount of the largest aftershock MW7.3 earthquake(<0.2 m).