A comparison of self-potential tomography with electrical resistivity tomography for the detection of abandoned mineshafts

We present a comparison of the abilities of Electrical Resistivity Tomography (ERT) and Self-Potential Tomography (SPT) to detect and characterize buried mineshafts at the site of a former colliery. Surface electrical resistivity and self-potential (SP) surveys were carried out at two test sites, each containing a hidden shaft. The ERT survey results indicate that both sites had a highly heterogeneous subsurface resistivity distribution, which we attribute to colliery spoil and former infrastructure. ERT managed to distinguish an air-filled, highly resistive mineshaft from this background, but failed to detect the second shaft, which was backfilled and therefore had a much lower resistivity contrast with the surrounding formation. However, SPT located both shafts, gave an indication of their size, shape and depth of burial, and was able to distinguish the open- from the backfilled mineshaft due to the strength of the associated SP anomalies. We argue that these SP anomalies are likely to be due to changes in the streaming potential caused by preferential drainage into the shafts.