Research On Shallow Velocity Inversion Method Combining Surface Wave And Body Wave Information

The velocity information of near-surface P-wave and S-wave runs through all links of shallow seismic geophysical prospecting,so the acquisition of shallow velocity parameters is of great significance in the shallow geophysical prospecting.Refractive wave method and surface wave method have been widely used in shallow geophysical prospecting,but there are some problems with them.Among them,Rayleigh wave dispersion curves inversion has been most commonly used to obtain near-surface shear waves velocity profile,which is a highly nonlinear,multi-parameter,and multi-peak inversion problem,and the velocity of P-wave is selected by experience according to the actual geological situation.In order to overcome such problems,a joint inversion of Rayleigh wave dispersion curve and refraction travel time using the shuffled frog-leaping algorithm(SFLA)has been present.Refraction travel time could provide primary wave data for Rayleigh wave dispersion inversion.The joint inversion only takes the formation density as the known quantity to invert the shear wave velocity,primary wave velocity and formation thickness.The SFLA is a promising global searching algorithm that has the advantages of few parameters,rapid speed of convergence,strong capability of global search,and can improve the speed and accuracy of inversion.This thesis mainly carries out three aspects of research:(1)Introduce the application of swarm intelligence optimization algorithm,and expound the basic principle and operation flow of shuffling frogging algorithm.For different inversion cases,different objective functions are developed.After several tests,the optimal parameter combination suitable for different inversion conditions was determined.(2)Carry out Rayleigh wave dispersion curve inversion for the synthetic model,and compare and analyze the inversion results with the inversion results of particle swarm optimization algorithm(PSO),so as to prove the reliability and computing ability of SFLA.Then we inverted a real-world example to examine the applicability of SFLA.(3)Combined refraction wave travel time and Rayleigh wave dispersion curve inversion method based on SFLA is adopted to make up for the limitation that the P-wave velocity can only depend on geological experience when using Rayleigh wave dispersion curve individual inversion.The joint inversion results of synthetic model and field data are respectively carried out,and the inversion results are compared with the results of.The inversion results of theoretical model and measured data show that the joint inversion of Rayleigh wave dispersion curve and refraction wave travel time based on shuffle frog-leaping algorithm is more accurate and reliable than that of Rayleigh wave dispersion curve individual inversion,which are closer to the real situation.The comparison between the inversion result of shuffling frog-leaping algorithm and that of particle swarm optimization algorithm proves that shuffling frog-leaping algorithm is more advantageous in calculation accuracy and speed.