Developments in passive seismic techniques through the ANSIR National Research Facility

Since 1997 the ANSIR Major National Research Facility has significantly enhanced Australia?s national capacity for recording regional and distant earthquakes using seismic recorders distributed across the continent. Both broad-band and short-period recorders have been deployed in innovative experimental designs that have made major contributions to the understanding of the 3D structure in the Earth?s crust and upper mantle beneath the Australian region. The Facility continues its national role with investment in equipment suitable for both seismic and electromagnetic sounding. Deployments of recorders with broad-band seismometers have made a substantial contribution to surface wave tomography, particularly with the gathering of extensive data sets from Western Australia and a deployment bracketing the Tasman Line. The significant increase in the number of portable stations provides constraints on the character of the crust and the crust-mantle interface across the continent, via the analysis of receiver functions from distant earthquakes. Anisotropy beneath the continent is now better characterised but remains enigmatic. New analysis methods are likely to make more extensive use of continuous seismic data. Short-period instrument deployments have been mostly directed towards delay-time tomography studies in south-eastern Australia, and have employed new methods for event picking and tomographic inversion. Enhancements to the instruments mean that servicing of experiments will be simpler in future and allow new applications with three-component recording at higher sampling rates. Passive seismic recording offers a cost-effective way of obtaining structural information across substantial areas of the continent. The results are valuable in their own right, but can also provide important constraints on seismological structure that are valuable in planning more expensive deep crustal reflection profiles.