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Around the world the Earth's crust is blanketed to various extents by sediment. For continental regions, knowledge of the distribution and thickness of sediments is crucial for a wide range of applications including seismic hazard, resource potential and our ability to constrain the deeper crustal geology. Excellent constraints on the sediment thickness can be obtained from borehole drilling or active seismic surveys. However, these approaches are expensive and impractical in remote continental interiors such as central Australia. Recently, a method for estimating the sediment thickness using passive seismic data, the collection of which is relatively simple and low cost, was developed and applied to seismic stations in South Australia. This method uses receiver functions, specifically the time delay of the P -to- S converted phase generated at the sediment-basement interface, relative to the direct- P arrival, to generate a first-order estimate of the thickness of sediments. In this work, we expand the analysis to the vast array of over 1500 seismic stations across Australia, covering an entire continent and numerous sedimentary basins that span the entire range from Precambrian to present day. We compare with an established yet separate method to estimate the sediment thickness, which utilizes the autocorrelation of the radial receiver functions to ascertain the two-way traveltime of shear waves reverberating in a sedimentary layer. Across the Australian continent the new results match the broad pattern of expected sedimentary features based on the various geological provinces. We are able to delineate the boundaries of many sedimentary basins, such as the Eucla and Murray Basins, which are Cenozoic, and the boundary between the Karumba Basin and the mineral rich Mount Isa Province. Contrasts in seismic delay time across these boundaries are upwards of 0.4  |$\, \mathrm{s}$|⁠. The delay signal is found to diminish to <0.1  |$\, \mathrm{s}$| for older Proterozoic basins, likely due to compaction and metamorphism of the sediments over time. As an application of the method, a comparison with measurements of sediment thickness from local boreholes allows for a straightforward predictive relationship between the delay time and the cover thickness to be defined. This offers future widespread potential, providing a simple and cheap way to characterize the sediment thickness in underexplored areas from passive seismic data. [ABSTRACT FROM AUTHOR]

A blanket of sedimentary and regolith material covers approximately three-quarters of the Australian continent, obscuring the crustal geology below and potential mineral resources within. Sedimentary basins also trap seismic energy increasing seismic hazard and generating noisy seismograms that make determining deeper crustal and lithospheric structure more challenging. The most fundamental question that can first be asked in addressing these challenges is how thick are the sediments? Borehole drilling and active seismic experiments using a controlled seismic source (e.g. vibroseis) provide excellent constraints, but they are limited in geographical coverage due to their expense, especially when operating in remote areas. On the other hand, passive-seismic experiments that involve the deployment of seismic receivers only (i.e. seismometers) are relatively low-cost and portable, providing a practical alternative for initial surveys. Here we utilize receiver functions obtained for both temporary and permanent seismic stations in South Australia, covering regions with a diverse sediment distribution. We present a straightforward method to determine the basement depth based on the arrival time of the P -converted-to- S phase generated at the boundary between the crustal basement and sedimentary strata above. Utilizing the available borehole data, we establish a simple predictive relationship between Ps arrival time and the basement depth, which could then be applied to other sedimentary basins with some consideration. The method is found to work best for Phanerozoic sediments and offers a way to determine the sediment–basement interface in unexplored areas requiring only temporary seismic stations deployed for < 6 months. [ABSTRACT FROM AUTHOR]

From 2008 to 2011 a broadband seismic array (BILBY) spanned the Australian continent from North to South, crossing the suture zone between the North and South Australian cratons, and traversing the Central Australian orogenic belt. Past tectonic events, including orogenies during the Proterozoic and Paleozoic, have left a long-lasting impression on the crustal and Moho structure of this inter-cratonic region. However, the impact of past tectonic activity on the lithosphere has been less clear. Here we present the first shear-wave splitting results for the BILBY array using a combination of SKS and PKS teleseismic phases to investigate patterns of deformation and seismic anisotropy within the upper mantle beneath central Australia. Null *KS observations are found to be abundant compared to observations of splitting, as has been widely reported by previous studies, but this appears to be largely due to a coincidental alignment of the inferred anisotropic fast direction with the back-azimuthal range at which most available events occur (140°-160°). Across the central Australian belt the station averaged fast directions tend to orientate ENE-WSW parallel with topographic, gravity, and magnetic trends. Northwards however, the fast directions switch orientation, instead following the NW-SE elongated geometry of the Tennant Creek Inlier, thus delineating a sharp lateral change in the underlying seismic anisotropy. Overall, evidence suggests that the splitting pattern likely reflects anisotropy inherent within the lithosphere generated by past deformational events over 300 million plus years ago, as opposed to the present-day mantle flow in the asthenosphere. While two distinct layers of anisotropy, present in both the asthenosphere and lithosphere, is supported by other evidence, it is not necessarily required by our current dataset. Instead, we can sufficiently model our results with only a single layer of anisotropy, consistent with the expected geometry of azimuthal anisotropy in the lithosphere. • *KS splitting presented for the BILBY array in Central Australia. • Splitting pattern shows strong resemblance to the surface geology • Reflects anisotropy generated by past lithospheric deformation of the continent. • Suggests past tectonic events substantially impacted both crust and lithosphere. [ABSTRACT FROM AUTHOR]