Earth Physics
Click on the links below to read the 2006 Earth Physics research highlights Or download the 2006 Earth Physics Research Highlights in PDF format HERE  1.47Mb
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Introduction
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
Geophysical Fluid Dynamics Research highlights
Seismology & Mathematical Geophysics Research Highlights
