Analysis and interpretation of anomalous conductivity and magnetic permeability effects in time domain electromagnetic data Part I: Numerical modeling

Time domain electromagnetic (TDEM) response is usually associated with eddy currents in conductive bodies, since this is the dominant effect. However, other effects, such as displacement currents from dielectric processes and magnetic fields associated with rock magnetization, can contribute to TDEM response. In this paper we analyze the effect of magnetization on TDEM dat a. We use a 3-D code based on finite-difference method, developed by Wang a nd Hohmann [Geophysics 58 (1993) 797], to study transient electromagnetic f ield propagation through a medium containing bodies with both anomalous con ductivity and anomalous magnetic permeability. The remarkable result is tha t the combination of anomalous conductivity and permeability within the sam e body could increase significantly the anomalous TDEM response in comparis on with purely conductive or purely magnetic anomalies. This effect has to be taken into account in interpretation of TDEM data over electrical inhomo geneous structures with potentially anomalous magnetic permeability. (C) 20 01 Elsevier Science B.V. All rights reserved.