Parallel-Swath-Arrays Analysis Of Passive Surface Waves Based On Beamforming

With the rapid development of urbanisation in China,passive source surface wave exploration methods have attracted increasing attention in the exploration geophysical community because of their advantages such as high efficiency,non-destructive and deep detection depth.However,when passive source surface wave measurements are carried out in complex environments,the noise source may have an azimuthal effect that breaks its assumption of smooth randomness,resulting in the phase velocity being overestimated and negatively affecting the subsequent inversion imaging.Therefore,it is important to study how to suppress the influence of the noise source orientation effect on passive source surface wave imaging in complex environments:(1)A Parallel-swath-arrays analysis of passive surface waves based on beamforming(PSAS)is proposed for suppressing azimuthal noise in complex environments such as cities.This method forms an array of parallel swath by adding one or more azimuthally constrained alignments to the observed alignments,and searches for noisy azimuths using a cluster beam analysis algorithm,the observed alignment was also subjected to dispersion analysis.The results show that compared to the single arrangement method,this method has a higher sensitivity to directional noise,can accurately search for noise azimuth,and its dispersion energy imaging results are more reliable.(2)The influence of array parameters on the azimuth search ability and dispersion imaging effect of PSAS is analyzed.Control of the alignment parameters by means of the control variable method,including the number of geophone channels,channel spacing,and array spacing.The results show that the increase in the number of detector channels enhances the PSAS azimuth search ability and dispersion imaging effect.The increase in channel spacing and array spacing both first improves and then decreases the azimuth search ability and dispersion imaging effect.The arrangement parameters have a significant impact on the PSAS noise azimuth search and dispersion imaging effect,and should be reasonably selected in practical applications.(3)PSAS was applied to weak noise environments in cities and strong noise environments in work areas,and ultra shallow and shallow two-dimensional shear wave velocity profiles were obtained for the two experimental areas.Reasonable explanations were made based on the actual environment of the work area and actual drilling data.The results showed that the noise orientation obtained by PSAS scanning was in good agreement with the actual noise distribution characteristics in the experimental area,The inversion results of dispersion curves have a good validation relationship with actual data,proving the value and potential of PSAS in suppressing azimuth noise in practical applications.