Comparing Seismic Refraction, Electrical Resistivity, and Ground Penetrating Radar in the Exploration of Mine Shafts: Case study in Centralia, PA.

Near surface geophysics methods have been used in karst hydrology, identification of underground void spaces and mine shafts. Centralia is well known for its extensive mine fire, and many abandoned mines with countless subsurface hallow space still exist in its basement. A site was chosen in Centralia as an experimental place to study the effectiveness of Seismic Refraction Tomography, Electrical Resistivity Tomography, and Ground Penetrating Radar in their ability to detect a mine shaft. All three surveys were performed along the same transect and the resulted output profiles from the three methods were compared. The comparison of these methods revealed that the ERT produced the best informative survey when compared with the results of the other two techniques. This is due to the highest apparent resistivity of air in the mine shaft making it easily detectable with ERT. The GPR showed strong reflection over the location of the shaft, matching the ERT profile. The method of SRT could not easily identify the mine shaft yet by using, a simple travel-time curve from a single energy source seemed to make its identification relatively easier. The study showed that, a simple travel-time curve of field seismogram can sometimes identify a mine shaft more effectively than an SRT profile. The seismic refraction worked better when an individual field seismogram with ray paths for forward and reverse traverses travel-time curves happened over the area with a subsurface shaft. The geometry of the correlation of travel-time curves with their wave paths to geophones for both forward and a reverse traverse gives a better method of identification of void spaces. The study showed that a combination of ERT and GPR seemed to be more suitable for this survey than any combination of any other two of the three methods.