Research On Forward And Inversion Of High Frequency Rayleigh Wave Method And Its Application In Engineering Site Investigation

The near-surface shear wave velocity is an important basis for the study of seismic design,seismic hazard coefficient analysis,and anti-shear properties of site media.Multichannel Analysis of Surface Waves(MASW)is an efficient method to obtain the vertical shear-wave profile.MASW mainly uses the large amplitude characteristic of high frequency Rayleigh wave to extract the near-surface Rayleigh wave frequency-velocity spectrum.And then pick the dispersion curve from the frequency-velocity spectrum according to some criterion.Finally,the dispersion curve inversion is performed to obtain the shear wave velocity profile.In this paper,the application of MASW in near-surface exploration is studied.The contents of this paper are as follows:(1)The multi-mode dispersion curve and the superposition mode dispersion curve of three kinds of common geologic models with four-layer incremental geologic model,four-layer low-velocity soft sandwich geologic model and four-layer high-velocity hard sandwich geologic model are calculated by multi-mode fast vector transfer method.And it is pointed out that it is feasible to carry out superposition mode dispersion curve inversion.It can effectively avoid the problem of mode aliasing;(2)Numerical simulation of Rayleigh Wave of the four-layer incremental geologic model,the four-layer low-velocity soft sandwich geologic model,the four-layer high-velocity hard sandwich geologic model and the four-layer incremental transverse graded geologic model are carried out by using the staggered-grid high-order finite difference.The frequency-velocity spectrum is extracted to compare with the superposition mode dispersion curve analysis solution.The details of Rayleigh wave numerical simulation are discussed detailedly;(3)The design problem of the observing system of geologic model with different wave velocity structure is discussed.The results show that for theincremental geologic model,the surface wave energy dominates the longest offset,followed by the low-velocity soft sandwich geologic model,and for the high-velocity hard sandwich geologic model,the surface wave energy dominates the shortest offset.And the scope and limitation of multi-channel analysis of surface waves are discussed;(4)Compare the resolution of the frequency-velocity spectrum and the accuracy of the dispersion curve extraction solution obtained by tau-p transform,frequency decomposition,high resolution linear Radon Transform(HRLRT).The results show that the resolution of frequency-velocity spectrum obtained by high resolution linear Radon transform is the highest and the accuracy of the dispersion curve extraction solution is also the highest;(5)Introducing the deterministic global optimization algorithm Generalized Pattern Search(GPS)to invert the dispersion curve.Dispersion curve of six-layer incremental geologic model,six-layer soft sandwich geologic model and six-layer high-velocity hard sandwich geologic model is inversed.The inversion results show that the GPS algorithm can reconstruct various geological model with high precision;(6)Finally,the superposition mode dispersion curve inversion in this paper is applied to the measured data of Jilin University campus site to produce one-dimension shear wave velocity profile.According to the method of one-dimension shear wave velocity profile acquisition,a number of measured data of two survey line are processed and a number of one-dimension shear wave velocity profiles are obtained,and a number of one-dimension shear wave velocity profiles are combined into two-dimension matrices.After the interpolation,the two-dimension shear wave velocity profile can be obtained.