Wave Field Characteristics and Transmission Processing of Seismic Waves in Coal Seams with Non-Developing Fundamental Mode Channel Waves

Fine detection of geological structures in the working face of mines can provide a strong geological guarantee for safe and efficient production. The channel wave seismic method is an effective geological guarantee technology; however, it is only effective for coal seams wherein channel waves develop well. It does not yield acceptable results for coal seams in which channel waves develop poorly or fail to develop. To address this problem, the Kelvin–Voigt viscoelastic model and the staggered grid high-order finite difference method were applied to study the propagation and attenuation characteristics of the seismic wave field in viscoelastic coal seams. Moreover, the causes for the non-development of channel waves were explored. Numerical simulation and a field experiment on transmitted channel waves were performed for fault structure detection in coal seams. The effects of refracted longitudinal waves, multiple shear horizontal (SH) waves, and first-order Rayleigh channel waves on fault structure detection in models with different fault throws were investigated. The results indicate that the coal seam transverse wave quality factor Qs has a significant influence on the absorption attenuation of Love channel waves and fundamental mode Rayleigh channel waves. However, it has minimal influence on refracted longitudinal waves, first-order Rayleigh channel waves, and multiple SH waves. When the fault throw is greater than or equal to the coal seam thickness, the first-order Rayleigh channel waves and multiple SH waves can accurately reflect the fault location and extension shape, and the refracted P waves can accurately locate the faults but cannot accurately reflect the fault extension shape. When the fault throw is half the coal seam thickness, the refracted P waves and multiple SH waves have a poor detection effect, but the first-order Rayleigh channel waves can accurately reflect the fault location and extension shape. For working faces in which fundamental mode channel waves develop poorly, first-order Rayleigh channel waves can replace the fundamental mode channel waves in seismic methods to locate geological structures in coal seam working faces.