Multichannel Analysis Of Surface Waves Under Rolling Topography

The traditional multichannel surface wave analysis method is not suitable for the rolling topography condition,which limits the practical scenarios of multichannel surface wave analysis method.This paper explores the multichannel surface wave analysis method of rolling topography from two aspects: forward modeling method and inversion strategy of surface wave dispersion curve.Based on the principle of beam analysis with amplitude normalization weighting,a forward modeling method for multichannel Rayleigh wave dispersion curve of medium model is proposed,which is applicable to surface fluctuation and stratum interface level.This method divides the underground medium into several local units.For each local unit,the traditional forward modeling method of dispersion curve is still used to obtain its local phase velocity.Based on the principle of bunching analysis,the relationship between the overall phase velocity of the medium under the multi-channel surface wave arrangement and all the corresponding local phase velocity of the arrangement is obtained.The theoretical dispersion curve of multichannel Rayleigh wave data under rolling topography is obtained.The numerical analysis results show that,compared with the traditional forward modeling results,the forward modeling results of the proposed method have a better agreement with the ones extracted by using wave field simulation seismogram.The traditional inversion parameters of multi-channel surface wave dispersion curve are generally the velocity and thickness of stratum shear wave.For rolling topography,the thickness is not consistent at each local position,so it cannot be used as the inversion parameter.Therefore,this paper proposes an inversion strategy which takes formation S-wave velocity and formation interface elevation as inversion parameters,and uses particle swarm optimization algorithm to invert the dispersion curve,so as to realize the inversion of multichannel surface wave dispersion curve in rolling topography.A typical geological model is established to simulate the seismic record,and the S-wave velocity imaging is carried out by using the forward method of dispersion curve and inversion strategy in this paper.The results correspond well with the geological model,indicating the effectiveness of the proposed method.