The AusArray SA broadband seismic array project will use passive seismology to develop 3D models of the deep subsurface to support mineral prospectivity mapping. This project is a collaboration between the GSSA, Geoscience Australia and the Australian National University.
Craton margins are locations favourable to the development and preservation of large mineral systems. The Gawler Craton is no different; it is recognised as highly prospective, but exploration is hindered by the fact that less than 3% of the craton is exposed at the surface. This motivates the need for innovative geophysical approaches to support exploration of the subsurface. The AusArray SA broadband seismic array will use passive seismic data (earthquakes and the ambient noise field) to map the 3D structure of the craton from the deep upper mantle to the surface.
Past and present passive seismic arrays in South Australia.
The instrumentation from AuScope and Geoscience Australia will continuously record seismic data for 18 months at 38 locations at a regular spacing of ~0.5° across the eastern-central Gawler Craton. Drawing also on legacy datasets, the project team will apply a variety of passive seismic techniques to map the 3D structure of the crust and upper mantle beneath the eastern-central Gawler Craton, and beyond. The resulting models will provide unprecedented images of the South Australian lithosphere, delineating the detailed architecture (cover thickness, crustal thickness, lithospheric thickness, terrane margins, translithospheric faults, sutures and shear zones, etc) essential to robust prospectivity mapping.
The raw seismic data will be housed on the AusPass passive seismic data server and the derived model outputs will be made available on the South Australian Resources Information Gateway (SARIG). The seismic data processing will draw on the resources of the National Computational Infrastructure (NCI).
Dr JP O’Donnell presented an update to the AusArray project at Discovery Day.
Figure 1 shows a tomography slice in development using Rayleigh waves extracted from seismic ambient noise. At this period, the waves are sensing the contrasting properties of sedimentary packages (slower wave speeds) and crystalline basement rock (faster wave speeds) in the upper crust. Tomography is performed at a range of periods to effectively step deeper into the Earth as the period increases.
Figure 1 Tomography slice in development.
In addition to modelling the latest tranche of data from the AusArray SA and Lake Eyre Basin array seismic stations, several legacy datasets covering the southeast of the state have recently become available on the Australian passive seismic server (AusPass). These valuable additions will expand the footprint of the modelling to encompass the southern Delamarian.
Figure 2 Map of legacy data sets in the southeast of South Australia that have recently become available.
All 38 AusArray SA seismographs and 30 Lake Eyre Basin array seismographs have been visited and serviced for this season. During this process memory cards are swapped, fresh batteries are added and any maintenance is undertaken. In total the team travelled over 14,500 km.
The next phase will be for this data to be analysed to support our development of subsurface structure mapping.
The next maintenance trip to the seismic stations is taking place in September 2021. The team will grab the most up to date information and carry out general maintenance of the equipment, as required.
Project lead, Dr John Paul O’Donnell, gives an overview of the AusArray SA project and what to expect as it moves forward:
The AusArray SA broadband seismic array is deployed across the eastern-central Gawler Craton. The MESA Journal article provides an overview of passive seismic techniques which will be applied to the data collected.