Seismic imaging of faults in multi-moded coal seams

Seismic energy propagating in a coal-seam waveguide can be used to map and detect acoustic discontinuities (such as microtectonic faults) occurring within the seam. Signals produced by an explosive source located in the mine roadway are scattered by such discontinuities, and may be recorded by an underground geophone array. Underground fault-imaging is complicated by the seam supporting more than one mode of propagation. By using direct signal arrivals from a known source location, modes are identified by means of their dispersion characteristic and particle motion. An array processor based on these properties is described. It can be used to selectively map a seam in a particular mode of propagation. The methods proposed are illustrated with field data, recorded at a mine in the United Kingdom.