Research On Comparative Analysis Of Dispersion Characteristics And Joint Inversion Method Of High-frequency Surface Waves

As a rapidly developing shallow surface geophysical technique in recent years,the highfrequency surface wave method is non-invasive,low-cost and highly efficient,and can quickly and accurately obtain the transverse wave velocity information of the subsurface medium,and its successful cases in urban underground space development and geotechnical engineering practical applications make it more and more important in the field of shallow surface geophysics.Compared with Rayleigh wave exploration,the limitation of lateral excitation required for Love wave exploration makes the research on Love wave exploration less applied.However,the simpler shape of Love wave dispersion curve,clearer dispersion energy and more stable inversion make Love wave exploration or combined Rayleigh-Love exploration an excellent complementary technique to high frequency surface wave methods.In view of the importance of Rayleigh and Love waves in shallow surface exploration,it is of great theoretical and practical significance to carry out the comparison of their dispersion characteristics,sensitivity analysis and joint inversion methods.Based on this,the following research elements were carried out in this paper:(1)Firstly,the study of dispersion curve orthorectification and dispersion curve extraction methods were carried out,and the dispersion characteristics of Rayleigh and Love waves in three typical geological models,namely,the cis-layer velocity model,the low-velocity sandwich model and the high-velocity sandwich model,were compared and analyzed,and the results showed that the dispersion curve characteristics of Love waves were simpler than those of Rayleigh waves.;(2)Secondly,the base order dispersion curves of Rayleigh and Love waves generated in three typical geological models,namely,the cis-layer velocity model,the low-velocity interlayer model and the high-velocity interlayer model,were used to compare and analyze the sensitive frequency bands of Rayleigh and Love waves at different stratigraphic depths.The results show that compared with the Rayleigh wave,the Love wave is more sensitive to the stratigraphic transverse velocity,although the presence of low-velocity and high-velocity interlayer significantly affects the sensitivity of Rayleigh and Love waves,and the sensitivity of Love wave is slightly higher than that of Rayleigh wave at low frequency.;(3)Then,the joint inversion of the Rayleigh wave and Love wave dispersion curves based on isotropic media based on the local gradient descent optimization algorithm is realized,and the model trial calculation of the method is carried out by using two typical velocity models,the accuracy of the inversion is evaluated by the error calculation formula,and the formation model is accurately restored by the results of the joint inversion,and the effectiveness of the joint inversion method in the actual stratigraphic medium is proved by using an actual data;(4)Finally,based on the difficulty of Love wave acquisition,Rayleigh and Love wave data are collected simultaneously using a vertical seismic source,and the dispersion characteristics and dispersion imaging results are compared and analyzed with the Love wave data collected by a lateral source,and the results show that the two have a high degree of consistency,and the dispersion energy of the two has similar continuity and signal-to-noise ratio by using superposition,which verifies the feasibility of using a vertical source to obtain Love waves in practical applications.