Self-potential (SP) is one of the few geophysical techniques that will detect electro-filtration effects associated with fluid flow in the subsurface.
However, the potential use of SP for environmental and engineering site investigations has, to-date, been severely inhibited by the lack of interpretational tools available for quantitative analysis.
A new tomographic image reconstruction scheme has been implemented. The algorithm is fast, robust, and makes no a priori assumptions about the subsurface charge distribution.
Unlike a simple contour plot, self-potential tomography (SPT) gives spatial information about the geometry of the causative source as a function of depth.
The new SPT technique has been successfully used to detect a concealed mineshaft (see Figure 1). The strong concentrations of charge are attributed to streaming potentials caused by preferential drainage into the shaft.
Other potential applications include the detection and monitoring of leaks from landfills, migrating solution cavities, or incipient landslides.
SPT monitoring of landslips could provide a better understanding of the fundamental triggering mechanisms associated with several types of gravity driven mass flow. This research involves theoretical modelling, controlled laboratory experiments, and field studies.
An ALERT system with both ERT and SPT sensors has been installed at an active landslip near Hollin Hill, Yorkshire. This installation uses a wind turbine and solar panel to recharge its batteries (see Figure 2).