The Inversion Calculation Of Rayleigh Surface Wave Dispersion Curves Based On Xi'an Ground Fracture Model

As an important branch of seismic exploration,surface wave exploration has been increasingly applied to solve shallow surface geophysics and geological issues.It has the advantages of non-destructive,high efficiency,strong anti-interference ability and high resolution of shallow layer.The main principle is to calculate the Rayleigh wave dispersion curve of the underground strata by forward modeling,and to reflect the underground stratum structure by the characteristics of dispersion curves to achieve the purpose of exploration.In this paper,the development history and research status of Rayleigh surface wave exploration technology are introduced in detail.Explains the propagation characteristics of Rayleigh surface waves.The effects of shear wave velocity,layer thickness,longitudinal wave velocity and density on the shape of dispersion curves were studied,and the variation of the dispersion curve as these three physical parameters change.Starting from the elastic wave equation,the Rayleigh wave equation is deduced..In the third chapter,two forward modeling methods of fast vector transfer algorithm and equivalent half-space algorithm are deduced.Combined with the relevant actual data of Xi'an ground fractures,a theoretical model that conforms to the actual conditions of Xi'an ground fractures is constructed and calculated.Get two algorithms.The characteristics of the dispersion curve.Based on the characteristics of the dispersion curves,a fissure structure with a cut-off distance of only 1m can be determined,which lays a theoretical foundation for the application of the fast vector transfer algorithm and the equivalent half-space algorithm to the exploration of the ground fractures in Xi'an.The inversion calculation of Xi'an ground fracture model by genetic algorithm is realized.The algorithm can accurately calculate the dispersion curve of formation Vs structure and Rayleigh surface wave.The inversion calculations are performed on the two-layer model and the three-layer model.From the inversion results,the thickness of each layer and the shear wave velocity in each layer can be clearly determined.The position of the paleosol layer in the Xi'an ground fracture model can also be accurately determined.Reflected in the ground,it provides a theoretical basis for the application of the algorithm in actual exploration.The actual seismic exploration of Xi'an fissure fc2 was performed by the transient Rayleigh wave method.The effect was good,the exact location of the ground fissure could be judged,and the feasibility of the surface wave method in the actual exploration of the ground fissure was proved.