Preliminary study on wave field and dispersion characteristics of channel waves in VTI coal seam media

Coal seam is a sedimentary rock with bedding, which can be regarded as VTI medium. VTI medium model is more suitable for real coal seam. However, existing channel wave theories generally assume that coal seams are isotropic for mathematical simplicity, and there is no study on the properties of channel waves in VTI media. In this paper, we deduce the theoretical dispersion equation of Love channel waves in the three-layer VTI model and analyze the parameter effects on the dispersion curve for the first time. The channel wave field in VTI media is simulated by three-dimensional staggered-grid finite difference method. The results indicate that polarization of both qP- and qSV-waves is not parallel or perpendicular to the orientation of the wave traveling in VTI media, while the polarization of SH wave is normal to wave propagation direction at horizontal plane. Therefore, it is wise to use Love channel waves to conduct field exploration because of the uniqueness of dispersion curves in the VTI media for the Love channel waves comparing with that in isotropic media. The velocities of the Love channel wave in VTI media are higher than that in isotropic media. The coal seam thickness primarily influences the Airy frequency phase, while the Airy phase velocity remains stable. Both the S-wave velocity and gamma parameter of coal seam significantly affect Airy phase velocity. Severe errors may occur during in the coal thickness inversion when using the dispersion curve of Love channel wave in isotropic media, and dispersion curve in VTI media should be adopted. In terms of the amplitude distribution, Love channel waves appear to have similar patterns in both the VTI media and the isotropic media.