The Electrotelluric Survey Method
The Geophysics International Electrotelluric Survey Method is an environmentally passive geophysical technology used to evaluate the presence and relative quantity of fluid bearing zones in the subsurface. Information is derived by measuring the effects that telluric currents have on the Earth’s electric field at the surface. Telluric currents (Earth currents) are naturally occurring electrical currents which flow within the Earth. The flow of these electrical currents along a subsurface bedding plane induces an electromagnetic field at the bedding plane surface. (This occurs in much the same way that an electromagnetic field is induced around a man-made power line by the flow of an electrical current through the line.) The induced electromagnetic field at the bedding plane in turn radiates an electromagnetic wave back to the Earth’s surface where it is detected by a passive telluric receiver. The electromagnetic wave generated at the bedding plane contains specific information (e.g. thickness and relative porosity) about the adjacent rock layers from which it originated.