The propagation velocity of in-seam seismic (ISS) waves depends on frequency which is also known as dispersion. This dispersion is not only determined by the thickness of the coal seam and its dirt band content (i.e. thickness and position), but also by the rock type and its condition (soft or compact) above and below the coal. A coal panel completely surrounded by roadways was investigated using the in-seam seismic transmission survey technique. Along the roadways the immediate roof was either sandstone and shale. The seam thickness varied between 1.20 m (sandstone in the roof) and 1.40 m (shale in the roof) and a fault system (normal faults) crossed the panel with a total throw of about the seam thickness. Below this coal seam another coal seam with a thickness of about 80 cm exists. Its interval shown by exploratory drilling changes from about 60 cm to more than 6 m (seam splitting). Tomographic inversion was applied to the dispersion of the measured ISS waves and velocity distributions were calculated at frequencies found to be most sensitive to changes in the seam thickness and the distance to the coal seam below. By correlating the velocity distributions with known values along the roadways approximate distributions of the coal seam thickness and the seam splitting within the panel were produced. The mining of the coal panel had already been finished and comparison was made between the survey results and the actual situation as far as it was documented. Prediction by the seismic survey was partly in good agreement with the actual field conditions or showed at least the same trends.
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