Electrical Methods Overview

Bridging our subdivision of geophysical techniques into passive and active methods are the electrical and electromagnetic methods. Taken as a whole, the electrical and electromagnetic methods represent the largest class of all geophysical methods, some passively monitor natural signals while others employ active sources.

In addition to their great variety, this group of geophysical techniques represents some of the oldest means of exploring the Earth's interior. For example, the SP method described below dates back to the 1830's when it was used in Cornwall, England by Robert Fox to find extensions of known copper deposits. Natural electrical currents in the Earth, referred to as telluric currents, were first identified by Peter Barlow (pictured) in 1847. The EM method was developed in the 1920's for the exploration of base-metal deposits.

Electrical methods employ a variety of measurements of the effects of electrical current flow within the Earth. The phenomena that can be measured include current flow, electrical potential (voltages), and electromagnetic fields. A summary of the more well-known electrical methods is given below. In this set of notes we will consider only one of these methods, the DC resistivity method.