3-D seismic tomography of the Adelaide fold belt

Abstract

S U M M A R YA lithospheric tomography experiment was conducted in the Adelaide Fold Belt of South Australia, to elucidate the 3-D velocity structure down to depths of several hundred kilometres in a region of major geological and tectonic significance. The data comprised arrival times for compressional waves from 148 teleseismic events recorded on a temporary array of 40 digital seismographs spanning an area of 200 × 300 km. A new irregular shortest path ray tracer and non-linear inversion scheme were used to map the crust-and upper-mantle structure. Synthetic 3-D imaging tests were first performed to validate the procedure and establish resolution limits for the particular earthquake distribution and recording geometry.Wave speed anomalies of up to 4 per cent relative to the IASP91 layered earth model were found. The boundary between a prominent velocity high and a prominent velocity low in the shallow (crustal) depth slices seems to coincide with the synclinal axis of Adelaidean and Early Palaeozoic sediments. Other velocity features at shallow depths correlate with gravity highs and lows, and compare favourably with structure revealed from explosion seismic profiles recorded in the area. At depths greater than 60 km, the tomographic images reveal isolated velocity highs enclosed by regions of lower velocity within the fold belt. These features, of dimensions tens of kilometres, could indicate the existence of fragments of old mantle broken off from the thick subcontinental lithosphere beneath the Gawler Craton and scattered in the Rodinian break-up rift zone.

Transdimensional inversion of receiver functions and surface wave dispersion

“…Each array consists of between 30 to 60 short period instruments that continuously record for between five to ten months. Over the last decade, a total of over 500 sites have been occupied resulting in a very large passive seismic data set that has been used for several studies [e.g., Graeber et al , 2002; Rawlinson et al , 2006; Rawlinson and Urvoy , 2006; Clifford et al , 2007; Rawlinson and Kennett , 2008; Arroucau et al , 2010; H. Tkalčić et al, Multi‐step modeling of receiver‐based seismic and ambient noise data from WOMBAT array: Crustal structure beneath southeast Australia, submitted to Geophysical Journal International , 2011]. Here we focus on SEAL3, which is one of the twelve temporary deployments occupying the eastern and central sub‐province of the Lachlan Fold Belt located in New South Wales (Tkalčić et al, submitted manuscript, 2011).…”

New insight into Cainozoic sedimentary basins and Palaeozoic suture zones in southeast Australia from ambient noise surface wave tomography

“…The passive seismic data recorded so far has played a major role in unravelling the structure of the lithosphere in southeast Australia. This has mainly been in the form of teleseismic tomography [ Graeber et al , 2002; Rawlinson et al , 2006b, 2006a; Clifford et al , 2008; Rawlinson and Kennett , 2008] or combined wide‐angle and teleseismic tomography [ Rawlinson and Urvoy , 2006], the latter of which is restricted to Tasmania.…”

Structure of the crust and upper mantle beneath Bass Strait, southeast Australia, from teleseismic body wave tomography

“…We represent the seismic structure of the southeast Australian lithosphere using a two-layer model consisting of a crust and upper mantle separated by a Moho surface. Compared to previous teleseismic studies that exploit WOMBAT data to image the lithosphere beneath southeast Australia (Graeber et al, 2002;Rawlinson et al, , 2011Clifford et al, 2008;Rawlinson and Kennett, 2008;Fishwick and Rawlinson, 2012;Rawlinson et al, 2015, the work presented here uses a geographically more extensive dataset that also covers Bass Strait and northern Tasmania.…”