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Electrical and electromagnetic techniques can define the electrical
conductivity structure of the subsurface. In the upper few kilometers
of the crust, the electrical conductivity is controlled mainly
by the electrical properties of the material which typically
reflects the amount of water contained within the rocks and sediments.
With increasing depth in the crust, factors such as temperature,
intrinsic conductivity of minerals, and the possible presence
of molten rock are increasingly important in controlling the
electrical conductivity. Electrical and electromagnetic techniques
are widely applied in studies covering an enormous range of scales--from
searching for coins on a beach to studies of the structure of
the upper mantle. Typical applications include searching for
buried electrical lines, imaging archeological sites, engineering
problems, mapping saltwater intrusion into coastal aquifers,defining
hydrological flow and reservoirs, exploring for mineral and hydrocarbon
resources, analyzing geothermal systems, and in studying problems
associated with toxic waste dispersion. They also have been effective
in addressing problems related to volcanic activity and in crustal
structure and tectonic investigations.
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