Small geologic faults, invisible from the surface, frequently disrupt production of coal at mechanized faces in deep mines. Mine layout might be optimized if faults could be mapped from underground roadways. Channel wave seismology is an underground adaptation of surface reflection seismology, which relies on the fact that coal seams guide seismic energy. Coal in situ forms a natural two-dimensional waveguide.
The dispersion which this waveguide produces forms an obstacle to the accurate echo-ranging of underground faults. The obstacle can be overcome either with the aid of time-varying pulse compression filters or, as is demonstrated here, by a one-dimensional trace-by-trace form of frequency domain migration.
Distinctions other than dispersion between surface and underground survey data processing procedures are examined in the light of a case study of the mapping of faults buried within the Blackshale seam at Pye Hill colliery. Low data redundancy maps of the probable distribution of scattering in the vicinity of a buried 1-m fault are reconstructed using two variants of a Huygens-Kirchhoff migration, modified to handle the difference between group and phase velocity that is characteristic of dispersion.