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Exploration of Abandoned Mine Shafts by means of Seismic Refraction, Electrical Resistivity Tomography, and Ground Penetrating Radar: Case study at Centralia, PA

Near surface geophysical methods have been heavily used in mapping geological structures, and in the identification of mine shafts and underground void spaces. In this study, a site in Centralia, PA, was selected as an experimental site to study the relative effectiveness of Seismic Refraction (SR), Electrical Resistivity Tomography (ERT), and Ground Penetrating Radar (GPR) to detect abandoned mine shafts. Centralia is well known for its extensive mine fire, as well as many abandoned mines. All surveys were performed along the same transect at Centralia. SR and ERT were appeared to be the effective methods of mine shaft detection. Dipole-Dipole and Wenner ERT inversions detected the presence of 4 mine shafts with their respective placement in the subsurface. Standard Seismic Refraction Tomography (SRT) and SR Time-Distance Curves both identified the mine shafts in the subsurface. In travel-time curves, deviations from anticipated resultant velocities were indicative of P-wave propagation in void spaces. In SRT, graphical “depressions” across the 2D transect illustrate the location of the cavities. These indications of void surveys were seen in multiple SR transverses at Centralia and in a model survey. The study showed that both SR methods can image void spaces in the subsurface. The use of a GPR point-survey has indicated 5 mine shafts but had inconsistencies in the boundaries of the shafts. The study showed that a combination of ERT and SR seemed to be more effective for this survey than any other the combination of the three methods.