The electromagnetic (EM) inverse problem is nonunique, that is an infinite number of models fit the data if any do at all. One approach to this problem is to generate models which are maximally smooth in some sense, thereby assuring that the true Earth is rougher that the models. This it is unlikely that the models contain elements of structure which do not feature in the Earth. Also, the smooth inversions reflect the true resolving power of the EM method. We have developed this technique for most 1D problems and have an initial code which generates models for the 2D MT problem. The PIs will extend 1-D inversion to include the 2D resistivity problem, and to use these codes to examine resolution for 2D MT, resistivity and joint inversion. As important (or more so) as models generation is the matter of existence of a model which fits the data under the assumptions of dimensionality. While t;he existence problem has been solved for 1D MT and resistivity, little has been done for 2D existence criteria. Once the existence problem has been solved, the smooth inversion scheme is made more powerful, as the iterative inversions can be started from a feasible solution.
