Interpretation of local two-dimensional electromagnetic anomalies by formalized trial procedure

Summary. An iterative algorithm is presented to be used in the search for the shape of a 2-D local deep geoelectric inhomogeneity lying in a layered medium; an anomaly having been identified in the usual way by observing an alternating time-harmonic electromagnetic field along the surface of the Earth. The normal section parameters (conductivities and thicknesses) and the excess electrical conductivity (inside inhomogeneity) are assumed to be known. The shape of the inhomogeneity is determined by means of a misfit functional minimization technique. A gradient minimization algorithm is constructed and Tikhonov's regularization scheme is applied to achieve stability of the solution. The effectiveness of such an approach is demonstrated by model calculations and by the interpretation of the Carpathian geomagnetic anomaly. Finally, a brief discussion of the problems of the practical application of this formalized trial procedure is presented. Because of the lack of reliable estimates of the excess conductivity, it is proposed to consider a family of models selected for the set of probable values of model parameters. This family can be treated as a generalized solution of the interpretation problem.