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 associ ated 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 magnetizat ion. can contribute to TDEM response. In this paper we analyze the effect of magnetization on TDEM data. We use a 3-D code based on finite-difference method. developed by Wang and Hohmann [Geophysics 58 (I993) 797]. to study transient electrom agneti c field propagation through a medium containing bodies with both anomalous conductivity and anomalous magnetic permeab ility. The remarkable result is that the combination of anomalous conductivity and permeability within the same body could increase significantl y the anomalous TDEM response in compa rison with purely conductive or purely magnetic anomalies. This effect has to be taken into account in interpretation of TDEM data over electrical inhomoge neous structures with potentially anomalous magnetic permeability. © 200 1 Elsevier Science B.V, All rights reserved,