Analytical Solutions for the Total Field Magnetometric Resistivity (TFMMR) Technique

Abstract

The analytical solutions for the TFMMR parameter of the Sub-Audio Magnetics technique are important as a tool in indirect interpretation of the field data, in assessing which subsurfact structures will produce measurable signals, and for designing optimal field survey configurations. In this paper, we investigate the theoretical TFMMR anomalies that would be observed over simple model structures such as an homogeneous isotropic and anisotropic earth, vertical contacts or faults, inclined contacts, thick dikes and outcropping hemispherical-depression models. For each model, comparisons are made with the MMR method. In general, the magnitude and shape of the TFMMR signal varies with changes in the geomagnetic field. For 2-D structures, in particular, such as faults and dikes, the TFMMR and MMR methods produce signals of similar quality. In cases where subsurface conductive bodies are striking paralel to the line joining the electrodes, our results show that the MMR method produces relatively small signals whereas the SAM signal is still quite measurable. We have also shown that the TFMMR type responses is sensitive to the geomagnetic field rather than geological strike directions as MMR is. TFMMR measurements have higher resolution, higher data acquisition rate, lower field costs and higher amplitudes for certain subsurface geometries than MMR.