Earth Conductivity

Applying special mathematical techniques, researchers have used a combination of the measurements of the short period, naturally varying magnetic fields together with their companion electrical fields (magnetotelluric method) for local Earth-crust resistivity (1/conductivity) determinations. Magnetotelluric surveys have become an important part of most crustal geology studies (see Section 5.2.3, p. 128). With continental-size measurements of the daily variation field, scientists have produced a profile of the increasing Earth conductivity reaching into the upper mantle to depths of about 650 km (410 miles)—a little over one-tenth the way to the Earth's highly conducting center (Figure 2.24).

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