Contrasts in Cratonic Structure Within Australia From Surface Wave Tomography

Strong constraints are placed on the cratonic structure of Australia with the aid of an augmented data set and a re-inversion of the full set of surface wave paths. The new data set incorporates re-processed data from the temporary deployments SKIPPY, KIMBA, QUOLL and WACRATON alongside new data from TIGGER (01-02). Further data from an additional 14 permanent seismic stations is used to improve the uniformity of path coverage. The waveform procedure used to calculate each 1-D model is based on the automated code of Debayle (1999) with the additional use of multiple starting models. The use of multiple starting models gives an improved estimate of both the reliability of the 1-D path specific models and their errors. Approximately 1400 paths to temporary stations and 450 paths to permanent stations are accepted through the inversion procedure; thus avoiding the previous bias towards permanent station data. These 1-D models are treated as path averages within a conventional two-stage tomographic inversion and the resulting 2-D models are defined using a spherical B-spline function. Two of the main feature of these improved models are highlighted. Firstly, a very rapid change in the overall pattern of the velocity anomaly is observed between 75 and 100km deep for much of the Australian region. Secondly, the improved path coverage through Western Australia allows us to investigate the structure below the Pilbara and Yilgarn cratons. Below 150km a strong fast anomaly is seen beneath the Yilgarn Craton. Further North, beneath the Capricorn Orogen we see a distinct slow anomaly. Although slightly less well resolved, beneath the Pilbara region we see a grading back towards faster velocities in the very North.