A Magnetotelluric Traverse in Southern Australia

Abstract

Summary Telluric potentials were recorded at nine sites stretching 1000 km from east of Wilcannia (N.S.W.) to west of Coober Pedy (S.A.) in south central Australia. These were combined with data obtained from a simultaneous magnetic variometer study, and analysed to yield magnetotelluric impedance tensors. The estimation of probable errors for the impedance tensors was an important part of the calculations. Numerical calculations for two‐dimensional models showed that the observed data could be explained by a conductive‐resistive‐conductive layering. The top conductive (10 ohm‐m) layer is approximately 5 km deep and the ensuing resistive section (1000 ohm‐m) continues to a depth of about 230 km. This is underlain by an indeterminably thick conductive layer. Embedded in this general structure is an extremely good conductor (0.1 ohm‐m) which strikes north‐south. The detection of this good conductor is the main result of this work. The good conductor lies just east of the Adelaide Geosyncline at a depth of a few kilometres, and is of minimum thickness 10 km. It is thought to be related to the accretion of the eastern portion of the Australian continent on to the stable western Precambrian platform by tectonic processes. The strong anisotropy present in the magnetotelluric data at all sites could not be explained by induction in conductive sediments, and is thought to be caused by localized conductivity inhomogeneities distorting current flow. Copyright © 1973, Wiley Blackwell. All rights reserved