A SPECTRAL LANCZOS DECOMPOSITION METHOD FOR SOLVING AXISYMMETRICAL LOW-FREQUENCY ELECTROMAGNETIC DIFFUSION BY THE FINITE-ELEMENT METHOD

A new explicit axisymmetric solver for the diffusion of electromagneti c fields in an inhomogeneous medium is described. The proposed method is based on the Krylov subspace (Lanczos) approximation of the solutio n in frequency domain. The finite-element method (FEM) is employed to discretize Maxwell's equations. It is shown that the spectral Lanczos decomposition method (SLDM) is extremely fast. Furthermore, the electr omagnetic fields at many frequencies can be evaluated by performing th e SLDM iterations only at the lowest frequency. Analysis of some pract ical geophysical problems is included. A comparison is also made with the analytical results for a homogeneous medium.