A New Algorithm for 3-D Nonlinear Electromagnetic Inversion

We propose a new algorithm for 3-D electromagnetic inversion that works with the magnetic-field integral equation (instead of the traditional electric-field integral equation). The forward and inverse integral equations are discretized by the finite element method; solution of the matrix system involves alternating conjugate-gradient and biconjugate-gradient iterations. The solution is regularized by a novel external annealing technique. A coupled-domain decomposition allows a very efficient (96%) implementation of the algorithm on massively parallel machines. Tests on both synthetic and field data from environmental sites yield good subsurface images in a reasonable amount of computational time.