Magnetotellurics

Introduction

Magnetotellurics (MT) is the use of natural electromagnetic signals to image subsurface electrical conductivity structure through electromagnetic induction. The physical basis of the magnetotelluric method was independently discovered by Tikhonov (1950) and Cagniard (1953). After a debate over the length scale of the incident waves the technique became established as an effective exploration tool (Vozoff, 1991; Simpson and Bahr, 2005).

Basic method of magnetotellurics

Electromagnetic waves are generated in the Earth's atmosphere and magnetosphere by a range of physical processes (Vozoff, 1991). Below a frequency of 1 Hz, most of the signals originate in the magnetosphere as periodic external fields including magnetic storms and substorms and micropulsations. These signals are normally incident on the Earth's surface. Above a frequency of 1 Hz, the majority of electromagnetic signals originate in worldwide lightning activity. These signals travel through the resistive...