Magnetotellurics

Magnetotellurics is a geophysical method that estimates subsurface electrical resistivity from naturally varying magnetic and electric fields measured at Earth’s surface.

Magnetotelluric impedance: A frequency-dependent complex ratio between horizontal electric and magnetic field variations in magnetotellurics. Its amplitude and phase encode the subsurface’s electromagnetic response.
Geomagnetic pulsations: Quasi-periodic variations in Earth’s magnetic field, driven by processes in the magnetosphere and ionosphere. They provide natural electromagnetic energy across useful sounding frequencies.
Geothermal exploration: The search for heat, fluids, and permeable structures suitable for geothermal energy production. Conductive alteration zones and fluid pathways can stand out in resistivity models.
Seismic tomography: A method that reconstructs Earth’s interior from the travel times or waveforms of seismic waves. It images elastic properties, complementing magnetotelluric maps of electrical resistivity.
Andrey Tikhonov: A Soviet mathematician and geophysicist who helped establish the theoretical basis of magnetotelluric sounding. His work formalized how natural field variations reveal subsurface conductivity.
Skin depth: The depth at which an electromagnetic field’s amplitude in a conductor falls to about 1/e of its surface value. It explains why lower-frequency signals generally probe deeper structures.
Solar wind: A stream of charged particles flowing outward from the Sun and interacting with Earth’s magnetic environment. Its changing interaction with Earth contributes to some magnetotelluric source fields.
Mineral exploration: The search for economically valuable concentrations of minerals in Earth’s crust. Large resistivity contrasts can help locate sulfide deposits and their host structures.
Electrical resistivity tomography: A method that estimates subsurface resistivity by injecting current through electrodes and measuring resulting voltages. It uses controlled sources and usually shallower investigation than natural-source magnetotellurics.
Louis Cagniard: A French geophysicist who developed the magnetotelluric method in the 1950s. His formulation gave the method its practical framework and name.

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