Characterizing the cover across South Australia: a simple passive-seismic method for estimating sedimentary thickness

Abstract

Summary 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.

Refining the Moho across the Australian continent

“…This area of South Australia, particularly towards the north-east of the state, has a complex sedimentary overburden with multiple Phanerozoic sedimentary basins overlain on each other. As a result, receiver function time series are commonly dominated by strong reverberations which can obscure the signals from the crust and mantle (Agrawal et al 2022). A resonance filter, constructed using the properties of the autocorrelation of the radial receiver function (Yu et al 2015), proved to be useful in curtailing the sediment reverberation effect and thus aided the detection of the P-to-S conversion from the Moho (Agrawal et al 2023).…”

The Influence of Lithospheric Thickness Variations Beneath Australia on Seismic Anisotropy and Mantle Flow

“…The geological boundary demarcating cratonic Precambrian Australia from eastern Phanerozoic Australia is sometimes referred to as the Tasman Line (Direen & Crawford, 2003) (Figure 1). The precise location of the Tasman Line, inferred from various geophysical and geological observations is, however, often poorly constrained, especially in regions of thick sedimentary cover such as beneath the Lake Eyre region (Agrawal et al., 2022). Nonetheless, it is clear from Figure 1b that western Precambrian Australia is generally underlain by thick lithosphere (>150 km), whereas eastern Australia is characterized by relatively thin continental lithosphere, typically ∼75 km thick (Fishwick et al., 2008; Kennett & Salmon, 2012).…”

“…Compared to the Gawler Craton, the Curnamona Province is largely hidden under cover (Agrawal et al., 2022), but its oval‐shaped outline is easily distinguishable from aeromagnetic data (e.g., Williams & Betts, 2007). Sparse outcrops suggest that much of the province is composed of metasedimentary rocks of the late Proterozoic (1,715–1,640 Ma) Willyama Supergroup (Williams & Betts, 2007).…”