P-SV wave scattering by coal‐seam inhomogeneities

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Abstract
The dynamic finite‐element method is used to calculate the normal incidence P-SV guided‐wave scattering spectra of 124 models of coal‐seam obstructions commonly encountered in in‐seam seismology. The models are faults of varying throw and dip; thick faults with an associated region of fracturing; dikes of varying width, hardness, and dip; sills of varying hardness; stone rolls of varying height; and seam washouts. Reflection and transmission spectra including mode conversion are studied for incident fundamental symmetric P-SV seam modes. The dynamic finite‐element method is adapted to the calculation of scattering parameters through the consistent boundary condition of Lysmer and Waas. The results complement an earlier study of SH seam‐wave scattering. They show that faults reflect a much higher percentage of SH-wave energy than P-SV, but that P-SV-waves undergo substantially greater mode conversion on scattering from faults. Dikes exhibit thin film interferometric effects for both SH- and P-SV-waves. Sills do not reflect P-SV-waves substantially. Stone rolls cause conversion between symmetric and antisymmetric modes. From the results it is evident that reflection and transmission spectra contain sufficient information on the nature (not merely the existence) of a seam obstruction to justify further efforts in the design of in‐mine seismic observations aimed at allowing characterization as well as location of the obstruction. The names Evison wave and Krey wave are proposed and defined for guided SH-waves and P-SV-waves, respectively.

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