Electrical, electromagnetic, and magnetotelluric methods

Abstract

Application of electrical methods began with Robert W. Fox’s 1830 observation of self potentials associated with copper vein deposits in Cornwall. Conrad Schlumberger introduced the direct current equal potential line resistivity method in 1912. Harry W. Conklin received the first patents on the electromagnetic (EM) method in 1917. From these beginnings, the history of the development of the resistivity induced‐polarization (IP), magnetotelluric and EM methods are traced to the present time. It is of interest to note that application of electrical methods flourished from about 1920 to 1930, but then the methods were developed slowly until after World War II when a major burst of development activity took place. However, the interpretational basis of the methods remained poor until the last several years when application of numerical techniques using computers permitted forward and inverse solutions to electrical boundary value problems in two and three dimensions. Field hardware gradually evolved from 1960 through 1980 to permit precise broadband IP, electromagnetic, and magnetotelluric data acquisition with coherent detection and remote reference noise rejection, in‐field digital data processing and interpretation. The future of electrical methods is briefly sketched, with trends largely toward better numerical interpretation schemes, more broadband applications, more sophisticated use of in‐field digital acquisition processing and interpretation schemes, and accommodation of more channels of information.