Induced polarization

Abstract

In the chapter on resistivity methods one of the implicit assumptions made was that upon switching on the current between two current electrodes the voltage measured between the two potential electrodes was produced instantaneously. In general, this is not correct since the rise time of the voltage is finite. The delay in the voltage reaching its maximum value arises from a number of causes which may be broadly classified as instrumental effects and geological effects. The instrumental contribution to the delay time can be quite small and in those areas where the simple resistivity method is applicable the contribution to the delay time from subsurface geological causes is also too small to be of much use. However, there are some types of geological situations where the rise time is significant; this effect varies from place to place so the length of the rise time and the shape of the curve may therefore constitute a useful diagnostic method for exploration.