Crustal structure of southeast Australia from teleseismic receiver functions

Abstract

Abstract. In an effort to improve our understanding of the seismic\ncharacter of the crust beneath southeast Australia and how it relates to\nthe tectonic evolution of the region, we analyse teleseismic earthquakes\nrecorded by\xa024 temporary and 8\xa0permanent broadband stations using the\nreceiver function method. Due to the proximity of the temporary stations to\nBass Strait, only\xa013 of these stations yielded usable receiver functions,\nwhereas seven permanent stations produced receiver functions for subsequent\nanalysis. Crustal thickness, bulk seismic velocity properties, and internal\ncrustal structure of the southern Tasmanides – an assemblage of Palaeozoic\naccretionary orogens that occupy eastern Australia – are constrained by\n H – κ stacking and receiver function inversion, which point to the following:\n a\xa0 ∼ \u200939.0\u2009km thick crust; an intermediate–high V p / V s ratio\n( ∼ \u20091.70–1.76), relative to ak135; and a broad ( > \u200910\u2009km) crust–mantle transition beneath the Lachlan Fold Belt. These results are\ninterpreted to represent magmatic underplating of mafic materials at the\nbase of the crust. a complex crustal structure beneath VanDieland, a\nputative Precambrian continental fragment embedded in the southernmost\nTasmanides, that features strong variability in the crustal thickness (23–37\u2009km) and V p / V s ratio (1.65–193), the latter of which likely represents\ncompositional variability and the presence of melt. The complex origins of\nVanDieland, which comprises multiple continental ribbons, coupled with\nrecent failed rifting and intraplate volcanism, likely contributes to these\nobservations. stations located in the East Tasmania Terrane and\neastern Bass Strait (ETT\u2009 + \u2009EB) collectively indicate a crust of uniform\nthickness (31–32\u2009km), which clearly distinguishes it from VanDieland to the\nwest. \nMoho depths are also compared with the continent-wide AusMoho model in\nsoutheast Australia and are shown to be largely consistent, except in\nregions where AusMoho has few constraints (e.g. Flinders Island). A joint\ninterpretation of the new results with ambient noise, teleseismic tomography,\nand teleseismic shear wave splitting anisotropy helps provide new insight\ninto the way that the crust has been shaped by recent events, including\nfailed rifting during the break-up of Australia and Antarctica and recent\nintraplate volcanism.