Use of 3D seismic to image subsurface foundering due to gypsum dissolution.

We have used the seismic reflection method to image subsurface foundering due to gypsum dissolution in northern England. The objective was to evaluate the method for site investigation in places where there might be a subsidence hazard due to voids, whether in the form of old mineworkings or dissolution cavities. Here we focus on a 3D survey at one site where the seismic reflection method had previously been proved viable by acquiring 2D reconnaissance profiles. Seismic data were acquired on a limited budget, and the data were processed using standard algorithms. The resolution of the final time-migrated data volume was hampered by poor shot coupling and the presence of guided waves. Nevertheless, the results show that 3D seismic can reveal detailed images of subsurface foundering that could not be provided by any other method, even if supported by conventional grid of boreholes