A deep crustal electromagnetic sounding in the Georgia Piedmont

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Abstract
Electromagnetic soundings in the Georgia Piedmont using a horizontal loop source indicate an upper layer with conductivity variations from less than 2×10−5 to 2.5×10−4 S/m extending to about 15 km, underlain by a zone with conductivity of more than 10−3 S/m. At one site the conductance of any intermediate layer is limited to 2 S to a depth of 15 km. The conductivities of the upper layer agree with those expected from the surface geology, and the increase in conductivity occurs at a depth which correlates generally with reflections detected by the Consortium for Continental Reflection Profiling's seismic profile of the area. A possible source of the high conductivity is water saturated sediments trapped when the region was overthrust in the Appalachian orogeny.