Atelluric current (from Latin tellūs 'earth'), orEarth current,[1] is anelectric current that flows underground or through the sea, resulting from natural and human-induced causes. These currents haveextremely low frequency and traverse large areas near or atEarth's surface.Earth's crust andmantle are host to telluric currents, with around 32 mechanisms generating them, primarilygeomagnetically induced currents caused by changes inEarth's magnetic field due tosolar wind interactions with themagnetosphere orsolar radiation's effects on theionosphere. These currents exhibit diurnal patterns, flowing towards theSun during the day and towards thegeomagnetic poles at night.
Both telluric andmagnetotelluric methods exploit these currents for subsurface exploration, aiding in activities likegeothermal andmineral exploration, petroleum prospecting, fault zone mapping,groundwater assessment, and the study oftectonic plate boundaries. The phenomenon has also captured the imagination of authors, finding its way into fiction. InUmberto Eco'sFoucault's Pendulum, the search for a mystic center of the Earth connects to telluric currents, whileThomas Pynchon'sMason & Dixon incorporates them as enigmatic communication conduits alongsideHollow Earth theories.
Telluric currents are phenomena observed in the Earth'scrust andmantle. In September 1862, an experiment to specifically address Earth currents was carried out in the Munich Alps (Lamont, 1862).[2] Including minor processes, there are at least 32 different mechanisms which cause telluric currents.[3] The strongest are primarilygeomagnetically induced currents, which are induced by changes in the outer part of theEarth's magnetic field, which are usually caused by interactions between thesolar wind and themagnetosphere or solar radiation effects on theionosphere. Telluric currents flow in the surface layers of the Earth. The electric potential on the Earth's surface can be measured at different points, enabling the calculation of the magnitudes and directions of the telluric currents and hence the Earth'sconductance. These currents are known to havediurnal characteristics wherein the general direction of flow is towards the Sun.[4][5] Telluric currents continuously move between the sunlit and shadowed sides of the Earth, toward the equator on the side of the Earth facing the Sun (that is, during the day), and toward the poles on the night side of the planet.
Both telluric andmagnetotelluric methods are used for exploring the structure beneath the Earth's surface (such as in industrial prospecting). Formineral exploration the targets are any subsurface structures with a distinguishable resistance in comparison to its surroundings. Uses includegeothermal exploration,mining exploration,petroleum exploration, mapping of fault zones, ground water exploration and monitoring, investigation ofmagma chambers, and investigation of boundaries oftectonic plates.Earth batteries tap a useful low voltage current from telluric currents and were used fortelegraph systems as far back as the 1840s.[6]
In industrialprospecting activity that uses the telluric current method,electrodes are properly located on the ground to sense thevoltage difference between locations caused by theoscillatory telluric currents.[7][8] It is recognized that alow frequency window (LFW) exists when telluric currents pass through theEarth's substrata. In the frequencies of the LFW, the Earth acts as aconductor.[9]
The main plot of the 1988 novelFoucault's Pendulum byUmberto Eco revolves around conspiracy theorists who believe that they are searching for theUmbilicus Mundi (Latin for "The Navel of the World"), the mystic "Center of The Earth" which is supposed to be a certain point from where a person could control the energies and shapes of the Earth, thus reforming it at will. The novel takes this even further by suggesting that (in the view of the conspiratorialists) monuments like theEiffel Tower are nothing more than giantantennas related to these energies.[10]
Telluric currents, along what are effectivelyley lines, are discovered to be a means of mysterious communication in Thomas Pynchon's 1997 novelMason & Dixon and are associated with the book's Chinese-Jesuit subplot. As with Eco, cited above, Pynchon also reflects uponHollow Earth theories in this work.[11]
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