Theoretical basis and application of vertical Z-component in-seam wave exploration

Love seam waves are generally applied to the current in-seam wave explorations. Rayleigh seam waves, however, are rarely used. The dispersion and amplitude features of Rayleigh seam waves are investigated using frequency dispersion analysis and numerical simulations in this study. Firstly, we elucidate the advantages of using the vertical Z-component. Secondly, the theoretical basis standing behind its application to in-seam wave explorations is demonstrated. Furthermore, in order to compare the relative performances of Rayleigh and Love seam wave explorations, three-dimensional geological models with anomalies are numerically simulated. Thus, the feasibilities and actual exploration effects of Z-component in-seam waves are demonstrated for both theoretical models and practical applications. Our studies show that normal modes of Rayleigh seam waves always exist. Furthermore, the energy of the fundamental mode in-seam wave is concentrated in its Z-component for the middle of a coal seam. A compressional wave source primarily generates first-order mode Rayleigh seam waves whereas a shear wave source primarily excites fundamental mode Rayleigh seam waves, whose energy is concentrated in the Airy phase with the lowest velocity. The fundamental mode Z-components at the center of a coal seam are ideal for in-seam wave applications. Actually, fundamental and first-order mode in-seam waves can be recorded in most coal seams. The Z-component receivers can be placed at the location between 1/4 and 1/2 of the thickness of coal seam, where both wave modes could be detected.