| Abstract: | We have monitored changes in seismic velocity due to longwall coal-mining in the Selby coalfield, Yorkshire, England by. ten repeated surveys of a surface seismic reflection profile. The direction of face advance in the Barnsley Seam, at 550 m depth, was parallel to the orientation of the profile. The traveltime of a strong reflection event from an anhydrite bed at 150 m depth was measured after processing the data with standard techniques. As the face advanced, the traveltime increased by about 4% overall. In detail, the progressive increase in traveltime correlates well with empirical calculations of differential subsidence between the surface and the anhydrite. However, the magnitude of the change must principally be accounted for by a decrease in seismic velocity, which we attribute to a reduction in the vertical effective stress. |
