VUME Upper Mantle of the Earth

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Magnetotellurics (MT) is an electromagnetic geophysical method to study the distribution of electrical conductivity in the Eearth (imaging the earth's subsurface by measuring natural variations of electrical and magnetic fields at the Earth's surface).

Regions of enhanced conductivity hint at fluids, partial melts or metal deposits.
- Electromagnetic fields arise from time-varying currents in the ionosphere and tropical storms (lightning strikes).
- Fields propagate as plane-waves vertically into the Earth, inducing secondary currents.
- Earth's behavior is Ohmic (follows microscopic Ohm's law).
Investigation depth ranges from 300m below ground by recording higher frequencies down to 10,000m or deeper with long-period soundings. Developed in Russia and France during the 1950s, MT is now an international academic discipline and is used in exploration surveys around the world. Commercial uses include hydrocarbon (oil and gas) exploration, geothermal exploration, mining exploration, as well as hydrocarbon and groundwater monitoring. Research applications include experimentation to further develop the MT technique, long-period deep crustal exploration, and earthquake precursor prediction research.