Ambient noise tomography in Southeast Australia

Pierre Arroucau, Nick Rawlinson and Malcolm Sambridge

Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia

Figure 1. 2-seconds Rayleigh wave group velocity in Southeast Australia obtained from ambient noise cross-correlation of the vertical component for simultaneously recording pairs of stations. The stations used belong to 10 temporary arrays of short-period instruments deployed in the last decade.

Previous studies have demonstrated that the Green's function of the medium between two stations can be extracted from the cross-correlation of the seismic ambient noise wavefield recorded at these stations. This class of technique is now progressively becoming a standard seismic investigation tool and has  successfully been used for tomographic imaging purpose in many parts of the world. Saygin (2007) obtained encouraging results for the Australian continent using broadband records, and showed that Rayleigh wave group velocity contrasts within Australia correlated well with its major geological units.

In the last decade, dense rolling short-period seismic array deployments have been carried out by RSES in Southeast Australia (WOMBAT-SE). With an interstation distance of a few tens of km,  several months of continuous records and a cumulative total of approximately 400 stations, these temporary arrays provide an unique opportunity for high-resolution ambient noise imaging in the region, which can address fundamental questions regarding the structure and tectonic evolution of the Lachlan and Delamarian orogens, which underpin the southern half of Palaeozoic eastern Australia.

Dispersion curves constructed form the cross-correlation of the vertical component, by means of frequency-time analysis for periods ranging between 1 to 20s, have been used to extract Rayleigh wave group traveltimes. An iterative non-linear tomographic scheme based on the fast marching method, a grid-based eikonal solver, and a subspace inversion method, was used to map the traveltimes as variations in Rayleigh group wavespeeds at different frequencies.

Saygin, E, (2007) Seismic Receiver and Noise Correlation Based Studies in Australia. PhD Thesis, The Australian national university, 175p.