In-seam seismic methods: A Review

Abstract

Seismic reflection methods sample targets remotely from the vicinity of the ground surface. This, as much as the dimensions and physical properties of the target itself, imposes limitations on the resolution attainable. The coal mining industry has evinced a need for structural information on a scale smaller than is routinely attainable in reflection profiling, and at a range beyond the penetration of ground probing radar. Seismic waves generated and detected within a seam can in principle be used to delineate putative targets (faults, seam-splits, wash-outs, intrusions, and so on) of dimensions less than a seam thickness at a range (from a working face, say) or at least a few tens of metres. Dispersive channel waves of both Rayleigh and Lowe type are potentially most suitable for in-seam mapping (Krey, Geophysics, 1963). Notwithstanding the intuitive simplicity of so-called in-seam methods, practical implementations have proved elusive, as evidenced by intensive research projects in Germany, Britain, Czechoslovakia, the U.S.A., and recently Australia. To date, mathematical modelling and two-dimensional analogue scale modelling have both revealed characteristics of the generation and propogation of channel waves which bear importantly on the potential exploitation of these waves. In particular, Dresen and co-workers at the University of Bochum have shown how distinct Rayleigh-type wave groups arise from the interplay between source resonance effects and the propagation path transfer function. These and other important results from model studies underpin both the technical specification of in-seam systems, and the processing and interpretation of in-seam data. The published literature on in-seam methods is sparse, particularly with regard to technical specifications of high frequency sources and detectors suitable for safe operation in mines, or for operation in boreholes. The present paper reports on recent progress in in-seam research overseas.