Study On Quality Control Method For Extracting Dispersion Curve By Two-Channel Method Of Passive Rayleigh Surface Wave

In recent years,the passive-source Rayleigh surface wave exploration technology has developed rapidly,and its unique ability to use environmental noise as a signal source for exploration has certain characteristics,such as strong anti-interference ability,high mapping resolution,less restrictions in the acquisition process.Compared with the active-source exploration method,the passive-source surface wave exploration method is more suitable for exploration work in areas such as the surrounding areas.However,due to the low energy of the passive-source noise signal,the uneven distribution of the source and the lack of measurement time in the actual production survey,when the dispersion curve is extracted,the increase or absence of the spectrum zero will be caused,which will bring difficulties to the accurate extraction of the dispersion curve.The quality of the dispersion curve directly affects the final shear wave velocity inversion result.This thesis introduces the spatial autocorrelation theory and the principle of seismic noise interferometry proposed by Aki in the passive-source method.Aiming at the problems existing in the two-method extraction of the dispersion curve,this paper thesis improves the Gaussian filter by filtering the cross-correlation signal,controlling the length of the window and adding the control parameter m to the calculation of the phase velocity formula.By establishing a theoretical model and processing the actual data in the field of Fengxiang County,the feasibility and accuracy of the processing results can be verified.At the same time,after the passive-source noise signal is reconstructed by seismic interference technology,the active-source method is used to extract the dispersion curve,and the improved dispersion curve is compared and verified.The main research findings obtained in this thesis are as follows:(1)This thesis improves the method of extracting the passive-source surface wave dispersion curve by two methods.Based on spatial autocorrelation theory(SPAC)and two-channel method,the passive-source seismic noise signal is reconstructed.Different preprocessing methods are used to control the quality of the reconstructed seismic signal,and the accuracy of the dispersion curve is improved.(2)This thesis compares and analyzes the effects of different preprocessing and cross-correlation calculations and the length of time window on the extraction of dispersion curves,and gives the corresponding window selection principle.(3)According to the relationship between spatial autocorrelation theory and time domain cross-correlation theory,this thesis realizes the recovery of Green's function from passive-source signals,and the improved two-pass method is used to extract the dispersion curve of the passive-source Rayleigh wave.After comparing and analyzing the dispersion curves extracted by the unmodified Aki method,this thesis verifies the validity and accuracy of the improved two methods.