Ambient seismic noise tomography of Australian continent

Abstract

Imaging using information derived from the cross-correlation of the ambient seismic wavefield at different stations has recently become an important tool in seismology. We here present a continent wide study of the Australian crust based on the exploitation of continuous data from extensive portable broad-band deployments across Australia and the permanent stations. Permanent stations play a valuable role in linking the information from different portable deployments. Over 2000 Rayleigh wave components of the Green's functions are extracted from the inter-station cross-correlations and provide a reasonably uniform sampling of the continent. Rayleigh wave group velocities are extracted for the period range from 5 s to 12.5 s. The group dispersion from the various paths are inverted to produce group wavespeed maps based on a 2° × 2° grid using a nonlinear-iterative 2-D tomographic scheme with updating of propagation paths using the fast marching method. The group wavespeed maps display prominent features with lowered wavespeeds. For the shortest periods these features are mostly associated with the regions of thick sedimentary sequences, such as the Amadeus and Officer basins in central Australia. At the longer periods reduced wavespeeds are most likely due to elevated temperatures and link well to estimates of crustal heat flow. The major cratonic blocks show faster group wavespeeds, and the Archaean cratons of Western Australia are particularly fast with some indication of internal structure linked to terrane boundaries. The transition from the Precambrian core of the continent, in the centre and west, to the Phanerozoic fold belts in the east is not marked by any single well-defined anomaly in the crust, even though distinctive contrasts have been mapped in the mantle lithosphere from surface wave tomography.