Self Potential (SP) surveying, one of the oldest geophysical methods, involves passively measuring natural earth voltages. The method is commonly used in hydro geological and geotechnical applications.
The SP method involves measuring natural earth voltages using two electrodes at the surface. The natural earth voltages are typically caused by moving water and ions through pore spaces of soil and rock (electro kinetic potential). The potential drop (voltage) is measured between two non-polarizable electrodes at specific locations along the survey line. Typically, one electrode is placed in a fixed location, while the mobile electrode is placed at each reading location.
The depths of investigation for typical SP surveys range between 5 and 50 feet. The surveys are commonly conducted along with resistivity surveys in order to correlate features. Areas of water seepage are indicated by a sharp increase or decrease in the measured voltage. The data are presented as a graph of voltage versus survey location.