The rocks and minerals that make up the Earth’s crust and mantle have variable electrical properties. This characteristic is made use of in important methods of surveying, to research the structure and properties of the interior. Natural and induced electrical currents conform to the underground pattern of electrical resistivity. We describe how this can be used to locate anomalous regions with mineral enrichment or that have environmental importance. Electromagnetic methods, employed on the ground and from the air, are particularly important in mineral exploration. Ground penetrating radar has become an important tool of environmental and archeological research. These methods are limited to the top several hundred meters of the crust, but magnetotelluric methods can probe deeper into the lithosphere and mantle. The high-frequency variations of the magnetic field induce currents in the solid Earth and in the oceans, delivering valuable information about the electrical conductivity in the upper mantle.
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