Analysis of response characteristics of fault structural channel wave in viscoelastic coal seam

Buried fault is one of the important geological factors affecting the construction of transparent working face and the intelligent development of coal mine. Channel wave seismic exploration is a common method to detect fault at present. At present, the channel wave theory research is mainly based on the elastic isotropic condition of coal seam, but coal seam is a layered sedimentary rock mass composed of organic and inorganic materials, which has strong viscoelasticity. Based on Kelvin Voigt viscoelastic theory, the effects of coal seam viscoelasticity and fault displacement on channel wave propagation are studied by using three-dimensional staggered-grid high-order finite difference method and PML（ｐｅｒｆｅｃｔｌｙ ｍａｔｃｈｅｄ ｌａｙｅｒ） absorption boundary algorithm. The following conclusions can be obtained. The energy attenuation of seismic wave in viscoelastic medium coal seam is enhanced, and the energy attenuation of high-frequency part is serious. Viscoelastic medium is closer to the attenuation characteristics of actual coal seam. After the channel wave meets the fault, the high-mode Rayleigh channel wave of z component transmits and diffracts, resulting in a new converted waves（ｆｕｎｄａｍｅｎｔａｌ－ｍｏｄｅ ａｎｄ ｈｉｇｈ－ｍｏｄｅ Ｒａｙｌｅｉｇｈ ｃｈａｎｎｅｌ ｗａｖｅｓ）. When the coal seam Q_S=50, the fundamental-mode channel wave has an obvious dispersion curve shape. When the coal seam Q_S decays to 10, the high-mode Rayleigh channel waves is still clearly recorded, and the energy peak of channel waves moves to low frequency. With the increase of fault displacement, diffraction and transmission are gradually enhanced, and theenergy of converted wave group is gradually increased. After the fault, the converted wave group energy of z component gradually increases, the peak value of trough wave energy moves to high frequency.