Multistep modelling of receiver-based seismic and ambient noise data from WOMBAT array: Crustal structure beneath southeast Australia

Abstract

A limitation of most forms of passive seismic tomography using distant earthquakes lies in the fact that crustal structure is poorly resolved. An attempt is made here to address this issue by modelling teleseismic receiver functions (RFs) and dispersion curves derived from ambient noise through a multistep approach. The SEAL3 experiment in central and southern New South Wales (NSW) used here, represents one of 13 array deployments that so far comprise the large WOMBAT project, which aims to cover a significant portion of the Australian continent with a rolling array of seismometers. An interactive, forward-modelling software package (IRFFM2) is introduced and applied to the observed RFs and surface wave dispersion curves to define a prior, physically acceptable range of elastic parameters in the lithosphere, which is combined with a grid-search and a linearized inversion. Our results emphasize the importance of a joint treatment of RFs and dispersion data as the predictions from 1-D velocity models at individual stations derived from only RFs display large departures from the observed ambient noise dispersion curves. In total, 27 jointly constrained 1-D shear wave models are produced, which provide sufficient sampling of the crust beneath SEAL3 to permit detailed inferences about lateral variations in structure to be made. Of particular note is the observation that the Moho deepens towards the mountainous southeast, where it exceeds 50km in depth beneath the Southern Highlands of NSW, thus marking out some of the thickest crust in Australia. The complex lateral variations in mid-lower crustal velocity that we observe probably reflect the manifold interactions of a thinning lithosphere, associated igneous underplating, recent hot-spot-related volcanism and uplift. Our results image an important part of the lithosphere that is poorly constrained by regional and teleseismic tomography, and contribute to the understanding of the formation of the southern highlands and the Palaeozoic Lachlan Orogen. Show more