Program 3Dfeem: a multidimensional electromagnetic finite element model, Geophys

A suite of programs collectively referred to as 3Dfeem (3-D finite element electromagnetic model) has been developed to simulate the response of a given assemblage of conductors to a plane-wave or electric-dipole source. This application of the finite element method is based on the principle of minimization of energy; solution electric or magnetic vector fields are sought that minimize an expression giving the energy in the field and their sources at discrete points within the modelled volume. Solution fields are considered to be a superposition of ‘primary ’ fields, the response of a 1-D earth in the presence of specified source(s), and ‘anomalous ’ fields resulting from heterogeneities within the I-D model. Results from 2- and 3-D conductivity configurations are seen to be in favourable agreement with those from other computer simulators. Additionally, a comparison of solution fields from 3Dfeem and a 2-D analytic solution indicates that, with appropriate mesh spacing, 3Dfeem gives field estimates that are accurate to within about 8 per cent. An automesher program ensures that the error criteria are met. The method chosen to solve the set of finite element equations allows rapid estimation of the responses for perturbations in the conductivity structure of the starting model. The theory with which to allow discontinuous behaviour of the electric fields and the curls of the magnetic fields is discussed. Key words: electromagnetic modelling