2023-24 CSEG Distinguished Lecture: Magnetotellurics : Using natural radio waves to look inside the Earth

Geophysical exploration provides important information for resource exploration, studies of geohazards, and investigations into how the Earth works. Seismic exploration is the most widely used geophysical technique and is an invaluable tool for oil and gas exploration. However, no single geophysical technique can answer all questions about Earth structure. An alternative method uses low-frequency electromagnetic (EM) signals to image the electrical resistivity of the Earth. This rock property is sensitive to the presence of fluids and a number of economically important minerals. For more than a century, EM techniques have been applied in areas including hydrogeology, mineral exploration, and geothermal energy development. EM methods focused on near-surface exploration utilize signals generated with a transmitter. For deeper exploration it is most efficient to use magnetotellurics (MT) – an EM method that uses natural EM signals to image subsurface structure. 

In this lecture, I will describe the physics of the MT method and outline its range of applications. This lecture will emphasize (1) how MT is now capable of working in 3-D to develop realistic models of subsurface resistivity (2) how MT is most effective when used in combination with other geophysical methods, and (3) introduce applications of societal relevance including include mineral exploration, volcanology, geothermal exploration, and tectonic studies.