Detailed teleseismic imaging of the crust and upper mantle beneath southeast Australia

Abstract

Over the last decade, southeast Australia has been the focus of several teleseismic imaging studies that have mapped arrival time residual information from distant earthquakes as 3-D variations in seismic wavespeed in the upper mantle. Two of the most recent experiments are TIGGER and SEAL, which respectively involved the deployment of dense arrays of seismometers in northern Tasmania in 2002, and southern New South Wales and northern Victoria in 2004-2005. Tomographic imaging results from TIGGER show that the lithosphere beneath Tasmania is broadly characterized by (1) a marked transition from lower velocities in the west to higher velocities in the east. Significantly, the Tamar Fracture System does not overlie the narrow transition from lower to higher velocities; (2) an easterly dipping zone of relatively high velocity material beneath the Rocky Cape Group which may be related to remnant subduction of oceanic lithosphere. Tomographic imaging results from SEAL clearly reveal the west to east transition from Proterozoic to Palaeozoic lithosphere beneath the Murray Basin as a change from higher to lower velocities. Elevated velocities further east beneath the Wagga-Omeo Complex imply that the lithosphere beneath the central subprovince of the Lachlan Orogen is seismically distinct from that beneath the western subprovince. Our long term goal in southeast Australia is to combine the TIGGER and SEAL datasets with those from past, current and planned passive seismic arrays in order to construct a unified tomographic model of the entire region.