In an effort to improve our understanding of the seismic character of the crust beneath southeast Australia, and how it relates to the tectonic evolution of the region, we analyse teleseismic earthquakes recorded by 24 temporary and 8 permanent broadband stations using the receiver function method. Due to the proximity of the temporary stations to Bass Strait, only 13 of these stations yielded usable receiver functions, whereas seven permanent stations produced receiver functions for subsequent analysis. Crustal thickness, bulk seismic velocity properties and internal crustal structure of the southern Tasmanides – an assemblage of Palaeozoic accretionary orogens that occupy eastern Australia – are constrained by H-κ stacking and receiver functionκ stacking and receiver function inversion, which point to: (1) a ~39.0 km thick crust, an intermediate-κ stacking and receiver functionhigh Vp/Vs ratio (~1.70-κ stacking and receiver function1.76), relative to ak135, and a broad (>10 km) crust-κ stacking and receiver functionmantle transition beneath the Lachlan Fold Belt. These results are interpreted to represent magmatic underplating of mafic materials at the base of the crust; (2) a complex crustal structure beneath VanDieland, a putative Precambrian continental fragment embedded in the southernmost Tasmanides, which features strong variability in crustal thickness (23-κ stacking and receiver function37 km) and Vp/Vs ratio (1.65-κ stacking and receiver function193), the latter of which likely represents compositional variability and the presence of melt. The complex origins of VanDieland, which comprises multiple continental ribbons, coupled with recent failed rifting and intraplate volcanism, likely contributes to these observations; and (3) stations located in the East Tasmania Terrane and Eastern Bass Strait (ETT+EB) collectively indicate crust of uniform thickness (31-κ stacking and receiver function32 km), which clearly distinguish it from VanDieland to the west. Moho depths are also compared with the continent-κ stacking and receiver functionwide AusMoho model in southeast Australia, and are shown to be largely consistent, except in regions where AusMoho has few constraints (e.g. Flinders Island). A joint interpretation of the new results with ambient noise, teleseismic tomography and teleseismic shear wave splitting anisotropy, helps provide new insight into the way that the crust has been shaped by recent events, including failed rifting during the break-κ stacking and receiver functionup of Australia and Antarctica and recent intraplate volcanism.
The work in this paper was performed as part of a PhD study and has been jointly funded by Abubakar Tafawa Balewa University (ATBU), Bauchi, Nigeria and the University of Aberdeen, UK. The authors acknowledge the efforts of staff, students and fieldwork technicians from the Australian National University and University of Tasmania, who deployed the temporary BASS array used in this study. We also thank Qi Li and Armando Arcidiaco for their efforts in BASS data pre-κ stacking and receiver functionprocessing and archiving. Australian Research Council Grant LP110100256 supported the BASS deployment. We are grateful to IRIS and Geoscience Australia for providing data from several stations in mainland Australia and Tasmania. Figure 1 was made using Inkscape software
This research has been supported by the Australian Research Council (grant no. LP110100256).
- receiver functions
- crustal structure
- Bass Strait
- SE Australia