Telluric current
A telluric current (sometimes referred to as Magnetotelluric) is a extremely low-frequency electrical current that occurs naturally over large underground areas at or near the surface of the Earth. Magnetotelluric includes the magnetism component of the natural circuit.
Telluric currents are influenced by the conductivity in the interior of the Earth. Telluric currents are induced by changes in Earth's magnetic field, which are usually caused by interactions between the solar wind and the ionosphere. Telluric currents can be measured and, after being normalized, provide information about current direction and the conductance.
Both the telluric and magnetotelluric methods are used for exploring the structure beneath Earth's surface. For mineral exploration the target is conductive ore bodies. Other uses include exploration of geothermal fields, petroleum reservoirs, fault zones, ground water, magma chambers and plate tectonic boundaries.
The Unites States Patent office has a division classification for geophysical electrical measuring devices of the telluric type (including magneto-telluric types).
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