Electrical conductivity anomalies and continental seismicity in Australia

Abstract

WHERE the Upper Mantle Project ‘geotraverse’ line in western Australia crosses seismic zones anomalous effects have been found in the vertical component of the magnetic fluctuation field1. A two-dimensional array study operated over a wide area of southern Australia has detected anomalous effects at the eastern edge of the seismically active Flinders Ranges2. Various interpretations have been suggested for the Flinders anomaly2 and interpretations of the accompanying seismicity3 have been given in terms of plate tectonics4. Independent seismic evidence5 indicates that there is no abrupt step in crustal and upper mantle structure from west to east across the Flinders Ranges, though there may be a gradual change. A magnetometer array in south-eastern Australia has detected anomalous effects in southern Victoria6, and the interpretation of a subsequent study has located the anomaly more exactly (F. E. M. L., unpublished), placing the conductor causing it under or near the Otway Ranges, another region of Australian continental seismicity. Consequently, all the major continental conductivity anomalies so far discovered in Australia are in regions of earthquake activity (Fig. 1).