Traveltime Inversion RAYINVR Algorithm Test And Application Of Crustal Structure Reconstruction In Zhenkang-luxi

A method of ray inversion for simultaneous of 2-D velocity and interface structure is presented by C.A.Zelt and R.B.Smith in 1992.Model parametric flexible setting velocity and interface node number and position,make the division of irregular quadrilateral mesh size is consistent with the condition of the underground medium by data resolution,largely avoided caused a parametric inversion illusion and less parametric cannot discern between fine structure defects.The application of the boundary layer smooth technology avoids the model parametric boundary point caused by the artificial rays focus and caustic,and receiver in the earth's surface caused by the objective of seismic ray shadow and triple phase phenomenon.In a quadrilateral with double linear interpolation,makes the internal ray tracing existing analytic solutions.Ray tracing test method is used to reach the observation point,greatly improving the efficiency of the algorithm.Inversion using damping least squares algorithm,improves the stability of the algorithm.The results are after walking to the number of rays,take compromise between residual and damping factor.The effect factors of the algorithm: experiments were conducted for the selection of damping factor,selection of initial model,test the influence of random error when the inversion results.Damping factor is the key factor that affect the algorithm efficiency and the result resolution.In the process of actual data processing,take big damping values will make inversion iteration lengthen,reduce the efficiency of the algorithm,and greatly reduces the resolution results;Take smaller damping values,may make inversion can't be.In order to improve the computation efficiency and distinguish better the end result,at each iteration needs to try out different damping values,this is very time consuming.we try to improve the damping factor selection,and doing the test.Our approach is in the initial iterative damping factor assigned to a larger value,through to the later in every step of the iterative value multiplied by a number of less than 1,gradually reduce the damping factor,increase the convergence speed and improve the resolution of the model parameters.Tests have shown that complete inversion takes only a few times to choose the multiplier can be less than 1.This improved greatly improve the computational efficiency.Rayinvr seismic traveltime inversion algorithm is essentially a kind of linear inversion algorithm,starting from the very different initial model inversion possible convergence secondary extreme value point,can't search the global optimal solution.To this,we adopt can get through the other two test observation data and the importance of the initial model to the inversion result,the selection of initial model should be combined with the prior information,when the observation data acquisition should also be accurate as far as possible.By reconstructing the crustal structure of the Zhenkang-Luxi section,the two-dimensional velocity structure of the area is re-obtained.In the inversion,the parameters and the initial model are selected based on the experimental content.The results are improved compared with the forward.The crustal structure is mainly composed of sedimentary layers,C1,C2,C3 and Moho strata.Each layer has obvious transverse velocity inhomogeneity,with the Honghe fault zone at 400 km,The east side of the high speed,Mo Ying deep depth of thickening.In the Xiaojiang fault zone appears obvious low speed,east into the South China continent for the stability of the block.