A LABORATORY INVESTIGATION OF ELECTRICAL ANISOTROPY IN PRECAMBRIAN ROCKS

Abstract

Laboratory electrical anisotropy measurements were made on selected dry metasediments and metavolcanics from the Precambrian complex of northern Michigan. Directional ac conductivity and dielectric‐constant values were obtained in six or more directions for each sample. These directional values were used to obtain a least‐square determination of the six independent coefficients needed to completely define the symmetric second‐rank, conductivity and dielectric constant tensors. Tensor principal values and directions were obtained from these coefficients. The results of this investigation indicate that metamorphic rocks may be characterized by strongly anisotropic electrical properties. The tensor representation surface symmetries reflect the symmetry of the rock fabric. Electrical anisotropy tends to increase, and the symmetry of the representation surfaces tends to decrease, at lower signal frequencies. The frequency spectra for all samples follow a relaxation‐type model, with critical frequencies occurring between 200 and 600 hz, indicating interfacial polarization as the dominant polarization mechanism.