Modelling And Inversion Of Rayleigh Wave Dispersion Curves

Shallow-surface S-wave velocity structure is important for earthquake safety evaluation,engineering survey,foundation treatment evaluation and seismic amplification estimation.It is of great significance for geological hazard prediction and mitigation to understand S-wave velocity structure.The most direct way to obtain the S-wave velocity structure is by drilling and logging,but the method is time consuming and costly.As obtaining S-wave velocity structure through surface wave exploration method is economic and efficient,it is widely used in the detection of underground S-wave velocity structure.The passive source surface wave method is a surface wave exploration method developed in recent years.It uses background noise as the "source".It does not require an artificial source and is particularly suitable for the detection of urban underground structures.Passive source surface wave exploration is based on the assumption that the received seismic waves are mainly surface waves.Based on the dispersion characteristics of surface waves propagating on the ground,the dispersion analysis method is used to separate surface waves from other seismic waves and the dispersion curves is extracted.Using the characteristic that the dispersion curve is most sensitive to the change of the shear wave velocity,the extracted dispersion curve can be used to invert underground shear wave velocity structure.The work completed in this dissertation mainly includes the following:(1)The theory of dispersion curve modelling and the root search method is first introduced in detail.Then the dispersion curve modelling algorithm was developed and a computation program was coded based on the algorithm.(2)The refraction microtremor method and the extraction method of the dispersion curve are introduced in detail.The refraction microtremor method is implemented using C language.(3)A systematic modeling analysis of the adaptability of the hyperbolic tangent function and the arctangent function models to fit the dispersion curves is performed.The problem of jumps appearing in the dispersion curve fitting is analyzed and a solution is proposed.(4)The concept of inversion and the inversion algorithm of the neighborhood are briefly introduced.The methods developed in this paper were applied to the detection of the shear wave velocity structure of the Lala Copper Mine and the S-wave velocity structure of the area was obtained.