Lithospheric sutures, continental fragments and hot spots revealed by a transportable seismic array experiment in southeast Australia

Beginning in 1998, passive seismic arrays have been progressively deployed throughout southeast Australia in an attempt to image the 3-D seismic structure of the underlying lithosphere at high resolution. To date, over 600 stations have been deployed as part of 14 separate arrays. Station spacing on the mainland is ∼50 km, which reduces to ∼20 km in Tasmania, an island that lies at the southern tip of the continent. The majority of stations use 3-component short period sensors (1 Hz natural frequency), but several of the early arrays use vertical component short period sensors, and a number of 3-component broadband sensors are distributed throughout. In the past, teleseismic traveltime tomography has been separately applied to data from most of the arrays. More recently, the emphasis has been on joint treatment of the data, with ambient noise tomography and teleseismic traveltime tomography being applied to multiple array data. The latest developments involve the use of an irregular grid approach for traveltime tomography which incorporates global ISC traveltimes as well as relative arrival times obtained from each array, thus enabling high resolution recovery of structure where justified by the path coverage. Differential attenuation tomography is also beginning to be applied, which complements the results obtained from the traveltime tomography. To date, a wealth of features have been revealed by 3-D seismic tomography, the most significant being: (1) an easterly dipping velocity transition zone which suggests that the older Delamerian Orogen extends beneath the younger Western Subprovince of the Lachlan Orogen; (2) a distinct region of low velocity in the upper mantle north of Melbourne, which can be associated with recent Quaternary hot-spot volcanism; (3) a gradual east-southeast decrease in velocity towards the coast, which is consistent with lithospheric stretching and thinning near a passive margin; (4) a zone of high velocity north of Adelaide that may correspond to the presence of the Palaeoproterozoic Curnamona Province at depth. In the case of the low velocity anomaly associated with recent hot-spot volcanism, it does not appear to extend in depth beyond ∼200 km, which may support the idea of edge-driven convection as a source rather than a mantle plume.