Studying the Earth's deep conductivity structures, important for developing our understanding of the dynamics of the Earth, is complicated due to effects of the shallow conductive structures on the electromagnetic (EM) responses for periods larger than hours. The results of the deep EM soundings can be heavily distorted by the surface shell conductance, which varies from fractions of Siemens (S) inland to up to tens thousand of Siemens in the oceans. Thus, separating the effects caused by those variations and by deep conductivity structures is an important step during interpretation of the data.
This article reports on efforts to overcome these difficulties by providing high-resolution, global maps of the Earth's surface shell conductivity structure, from which deep conductivity can be interpolated. Using finescale regional surface schemes of conductance for the shallow structures (S-maps) overlain and compiled into broader spatial maps, scientists will b e able to use data products from these efforts to accomplish research goals of the currently running USArray (http://www.emscope.org) and for the planned Euro-Array (http://www.euroarrayorg), projects that aim in part to regionally map the conductivity structures at upper and middle mantle depths by using magnetotelluric (MT) and magnetovariation (MV) methods.