Dictionary:Induced polarization (IP)
1. An exploration method involving measurement of the slow decay of voltage in the ground following the cessation of an excitation current pulse (time-domain method) or low-frequency (below 100 Hz) variations of earth impedance (frequency-domain or overvoltage method). Most of the stored energy involved with IP is chemical, involving variations in the mobility of ions (membrane polarization (q.v.) or the normal IP effect) and variations because of the change from ionic to electronic conduction where metallic minerals are present (electrode polarization, induced potential, or interfacial polarization); the latter is usually the larger effect. Various electrode configurations are used, especially the dipole-dipole array; see Figures A-18 and A-19. 2. The production of a double layer of charge at mineral interfaces or of changes in such double layers as a result of applied electric or magnetic fields. Compare SP (spontaneous or self potential).