The mantle beneath Australia

Abstract

The configuration of earthquakes around Australia enables these natural events to be used as probes into the seismic structure of the upper mantle. For the region below northern Australia, the combination of short-period and broad-band observations has enabled the construction of radial velocity profiles for P and S velocities and attenuation. There is a range of evidence for lateral variations in seismic velocity in the lithosphere and the upper mantle transition zone. The lateral variations in structure can be investigated directly by a number of techniques, including the analysis of travel-time residuals and waveform inversion, especially for surface waves. Line profiles have revealed strong contrasts in P velocities across the shield edge in southeastern Australia. Broader scale P wave tomography has extended the definition of three-dimensional structure, especially in the northern part of the continent. Surface wave studies have begun to reveal the three-dimensional variations in shear wave structure beneath the continent by exploiting the records from portable broad-band stations. These results show that some of the contrasts in surface geology between Precambrian and Phanerozoic outcrop are reflected in depth; some structures extend to depths of 200 km or more, e.g. the Mt Isa Block and the New England Block. Show more