Research On Modeling Of Seismic Faults And Inversion Of Slip Distribution

Geodetic observation technology provides strong technical support for surface deformation observation.In surface deformation observation,geodetic data can give full play to its characteristics of wide observation range and high observation accuracy,enrich the types of surface deformation observation data,and provide a new perspective for studying geophysical problems such as seismic fault dislocation.Using geodetic observation data to inverse seismic fault parameters is the research focus of geodetic inversion,and also the hotpot of researching the earthquake occurrence mechanism.The inversion of seismic source parameters can provide the basis for the study of fault slip,and also provide the foundation for studying seismic fault rupture,post-earthquake deformation,and seismic stress change.After obtaining reasonable seismic source parameters from inversion,the inversion of seismic coseismic slip distribution will become the key to analyze the mechanism of earthquake occurrence.In real life,seismic fault is often not a rectangular plane,and its structure is more complex.Therefore,it should be considered to build a non-planar fault model to fit the actual fracture situation of the fault.In this paper,the construction and application of seismic source dislocation model parameters and non-planar fault model are researched respectively.The main research contents and work of this paper are as follows:1.The nonlinear method of seismic source parameter inversion is studied.Combining with the nonlinear characteristics of seismic source parameter inversion and the characteristics of gradient-based optimizer（GBO）,which has fast convergence speed and is hard to fall into local optimization,the GBO algorithm is applied to the non-linear inversion of the source parameters of the Okada model of the simulated earthquake and the Lushan real earthquake,and its inversion results are evaluated for accuracy.The simulated seismic experiment results show that the algorithm is stable,and the multiple peak swarm optimization（MPSO）algorithm is closer to the true value.In the 2013 Lushan earthquake experiment,the root-mean-square error between the fault parameters obtained by the GBO algorithm and the surface observation shape variables is 3.703mm,it is slightly better than the 3.708mm calculated by the multi-peak particle swarm optimization algorithm.In addition,GBO algorithm is superior to MPSO algorithm in stability.The above results show that the introduced GBO algorithm has certain practical application value in the inversion of seismic fault source parameters.2.The variable dip fault models with different dip angles for different rectangular sub-faults are studied.Based on the fault rupture of the Lushan Ms7.0 earthquake in 2013,this research considers setting different dip for different sub fault to fit the actual rupture situation.Meanwhile,in combination with the coseismic GPS data of the Lushan earthquake,the source parameters and sliding distribution of the Lushan earthquake fault are inversed.Firstly,the gradient based optimizer（GBO）is used in nonlinear inversion to obtain the source parameters of the seismic fault.The strike of the fault is 206.52°,the dip is 44.10°,the length is 21.92km,and the depth is 12.79km.In order to refine the sliding distribution of the seismic fault,the seismic fault is divided into 3×3 sub faults.On the basis of the fixed central sub fault dip of 44.10°,the dip of other sub faults is obtained by iteration.Then,the model is further divided into a fault layer model composed of 23×19 sub fault slices,and the matlab fitting function is used to fit the dip of the 23×19 sub faults.Finally,the Lushan seismic fault plane is established as a shovel structure with steep upper and gentle lower,and steep south and gentle north.The slip distribution inversion results show that the depth of the slip peak is 13km,the corresponding maximum slip momentum is 0.67m,the seismic moment is 1.10×10¹⁹N·m,and the corresponding moment magnitude is Mw6.66,which is consistent with the research results of seismology.3.The method of polynomial interpolation to build fault surface model is studied.According to the actual rupture of the Lushan earthquake,this paper explores a new construction method when building the fault model:divide the building of the Lushan earthquake fault model into three stages.In the first stage,the plane fault model A is constructed using the gradient-based optimization algorithm（GBO）and the seismic source parameters obtained from nonlinear inversion of the Coseismic GPS data of the Lushan earthquake;In the second stage,the plane fault model A is segmented and the segmented seismic fault model B is constructed;In the third stage,based on the segmented seismic fault model B,the polynomial function interpolation method is used to fit the seismic curved fault model C.Based on the seismic curved fault model C,the slip distribution inversion is carried out and the results are analyzed.In the slip distribution results under this modeling method,the depth of the slip peak is 13km,the corresponding maximum slip amount is 0.68m,the seismic moment is 1.31×10¹⁹N·m,corresponding that,the moment magnitude is Mw6.71,which is consistent with the research results of seismology.