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Research Activities 2006

Earth Physics

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Research into the structure and dynamics of the Earth uses a range of physical and mathematical techniques and is grouped into the three themes of Seismology and Mathematical Geophysics, Geophysical Fluid Dynamics, and Geodynamics. The work spans observational, theoretical, laboratory, computational and data oriented studies that are all directed towards understanding the structure and physical processes in the solid and fluid Earth, and their environmental consequences.

The Area Coordinator for Earth Physics changed in September, from Prof B.L.N. Kennett (who took up the position of Director of the Research School) to Prof R.W. Griffiths (who was previously Interim Director of the School). New continuing appointments were made in observational seismology (Dr H. Tkalcic) under an initiative in earth sounding, and in ocean modelling (Dr A. Hogg) as a part of a broader ANU initiative in marine science. A further new continuing appointment (Dr M. Roderick) was made jointly with the Research School of Biological Sciences and the Faculty of Science in studies of the hydrological cycle and to coordinate the undergraduate ‘global and ocean sciences' program, again as a part of the marine science initiative.

Work in geophysical fluid dynamics this year includes the continued development of a new theoretical model for the thermohaline overturning circulation of the oceans, based on insight from laboratory experiments with ‘horizontal convection', turbulent entrainment into descending bottom currents and the ways in which the ocean overturning might respond to global warming and the consequent changes in the conditions at the ocean surface. Conditions required for the shutdown of deep sinking (the scenario of the popular movie “The Day After Tomorrow”) have been examined. Other laboratory-based investigations include studies of lava flow dynamics, which include cooling and solidification of yield-strength fluid flows, and three-dimensional simulations of subduction zones to understand the flow around subducting plates, the motions of trenches and the interactions of subduction with upwelling mantle plumes. Computational ocean modelling activity focused on inter-annual and decadal scale variability of the Southern Hemisphere circulation arising from eddy-mean flow energy exchanges in the Antarctic Circumpolar Current, and on thermal and mechanical coupling of the atmosphere and Southern Ocean.

Studies of the interaction of mantle dynamics with mantle chemistry, with the aid of new three-dimensional numerical models, suggest that early plate tectonics is a more viable concept than previously thought, which would change the expected cooling history of the mantle. Further, the age of mantle trace components depends little on the viscosity structure but mainly on the rate of processing through zones of melting.

During the year the Seismology and Mathematical Geophysics group was formed as an administrative banner covering activities in seismology and the centre for Advanced Data inference. In May seismic data was collected from the EVA array, a set of 50 short period vertical component seismometers deployed over much of eastern Victoria, and the instrument were removed. The data is generally of high quality, with a large number of tele-seismic earthquakes detected.

In early October 2006, an array of 40 3-component short period seismometers was deployed in southeast Tasmania as part of the SETA experiment. The array will be in place for a period of approximately 8 months to record large distant earthquakes. This project is in collaboration with colleagues at the University of Tasmania, who will carry out additional active source experiments that can be recorded by the SETA array. Tomographic analysis has been carried out using arrival time information from 90 distant earthquakes, and the resultant images exhibit significant lateral variations at 50-100 km depth between northern and southern Victoria.

Continuing analysis of data from the SSCUA experiment (2002-2004) in the unexplored region of Central East Antarctica, has revealed strain in the deep lithosphere that is likely to be related to relict structure in the most ancient blocks of the continent. New deployments associated with the International Polar Year (2007/08) are likely to provide additional seismic data to further investigate the remote interior of East Antarctica.

In the Centre for Advanced Data Inference projects have been conducted in seismic coda wave interferometry, airborne geophysics, ground motion estimation for seismic hazard assessment, statistical inference techniques, structural seismology, earthquake seismology and geodesy. This year saw continued development of the CADI inversion toolkit whereby CADI visitors and project participants have a simple interface to both software and hardware facilities including the Terrawulf parallel cluster.

The glacial rebound work in 2006 has focused on the Fennoscandian and Laurentide Ice Sheets from 40 Ka up to the present with the goal of establishing constraints on the ice thickness and ice margins for some of the major phases of the last glacial cycle. A major compilation of field evidence for the ice margin locations and shoreline elevations and sea levels across the region has been completed and the inversion of these has led to new ice models from 140,000 years to 60,000 years ago, including the time of the renewed initiation of the ice sheets after the last interglacial. Geodetic research during 2006 has continued to investigate ways of improving the accuracy of space-geodetic analysis, in particular modelling the temporal variation of the atmospheric propagation effects. New developments have been made in identifying and using persistent scatterers in Interferometric Synthetic Aperture Radar for ground deformation studies of the Australian continent. A successful re-observation of GPS sites was made in Papua New Guinea on a transect of sites along the western border, in the Schouten Islands, central Highlands and the Papuan Peninsula region.

Geodynamics Research Highlights

Relative Sea-level Changes due to Recent Mountain Deglaciation Gisela Estermann
Enhanced infrasound techniques for verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) Douglas R. Christie
Global Sea Level During the Last Interglacial Andrea Dutton
The deformation of Australia observed with InSAR John Dawson
Crustal Deformation observed by Space Geodesy Dan Zwartz
Advances in the analysis of space geodetic data Paul Tregoning
Water vapour feedback and global warming Peter Smythe

Geophysical Fluid Dynamics Research highlights

Geophysical Fluid Dynamics Introduction Ross Griffiths
Dynamics and Chemical Evolution of the Earth's Early Mantle Geoffrey F. Davies
Tectonic Evolution of the Earth Geoffrey F. Davies
Thermal Evolution of the Core Geoffrey F. Davies
Modelling the ocean thermohaline circulation in the laboratory Ross W. Griffiths
How does the Southern Ocean respond to changes in wind forcing? Andrew McC. Hogg
The Propagation and Morphology of Lava Flows Ross C. Kerr
Interaction of coherent eddies with headland wake flows Melanie J. O'Byrne
Mixing in ocean straits and overflows Tjipto J. Prastowo
Subduction kinematics and dynamics in 3D space: Insight from laboratory and numerical modelling W. P. Schellart
Three-Dimensional Flow and Temperatures in Subduction Zones Christopher Kincaid

Seismology & Mathematical Geophysics Research Highlights

Strengthening International Science and Science Commons - IAGA and e GY Charles Barton
Thermo-chemical Evolution of the Australian Continent Justin Freeman
Quantitative infra-red absorption spectroscopy Malcolm Sambridge
Constraining source location and mechanism using coda wave interferometry David Robinson
High resolution seismic imaging of southeast Australia using multiple array deployments Nick Rawlinson
Simultaneous inversion of active and passive source datasets for 3-D seismic structure Nick Rawlinson
Calibration and Inversion of Airborne Geophysical Data Ross Brodie
Geomagnetism Ted Lilley
Volcano-tectonic earthquakes and magma reservoirs; their roles in volcanic eruptions at Rabaul Caldera I. Itikarai
Historical earthquakes: a case study for Adelaide 1954 earthquake Cvetan Sinadinovski
P Wave Tomography of Western Australia
Agus Abdulah
Attenuation Tomography of Australia Agus Abdulah
Earthquake location and upper mantle structure from P wave polarization in French Polynesia and Australia Fabrice R. Fontaine
Tracking later arrivals in heterogenous velocity models Juerg Hauser
Lithospheric structure, past and present tectonics in Central East Antarctica Anya M. Reading
Group Velocity Tomography of Australian Continent from Ambient Seismic Noise Erdinc Saygin
Terrawulf projects in 2006 Malcolm Sambridge
Guided Seismic Waves from the Indonesian Subduction Zone to the Australian Craton Brian Kennett