A comprehensive study of mantle electrical conductivity will be carried out using both new and already published response functions. The work will bring together response functions for a variety of sources for combined interpretation, thereby obtaining the best possible spatial and frequency coverage. In the frequency bands where there are few data the PIs will supplement these response functions with new ones estimated from magnetic observatory data and from very long period MT data. Various new techniques for inverting geomagnetic data have been developed over the past few years, including the D+ existence algorithm, the funnel function approach, and the finding of smooth models through regularization of non-linear inverse problems. The PIs will apply these in a systematic way to the global response function collection to model mantle conductivity for the whole Earth. Extensions to the regularization approach will allow them to test various hypotheses about mantle conductivity structure; e.g. Is a jump in conductivity at the 670km seismic discontinuity consistent with or required by the data? Is there a depth below which lateral heterogeneity in conductivity is not required by the data? The answers to such questions may provide valuable insight into the physics of the Earth's interior.
