Induced polarization

Abstract

If an electric current in the ground is interrupted the voltage across P₁, P₂ (Fig. 39) does not drop to zero instantaneously. It is found instead to relax for several seconds (or minutes) starting from an ‘initial’ value which is a small fraction of the voltage (F) that existed when the current was flowing (Fig. 52). This phenomenon has been termed induced polarization and is easily observed when electronically conducting minerals or clay minerals are present in the ground. It was noted in geophysical work by C. Schlumberger some time before 1920 but modern application of the phenomenon to geophysical exploration dates from about 1948 although several, largely inconclusive, experiments were reported between 1920 and 1948.