Research School of Earth Sciences
The Research School of Earth Sciences includes substantial activities in geophysics. The main research themes are Geodynamics, Geodesy, Geophysical Fluid Dynamics, Mathematical Geophysics and Seismology. These span observational, theoretical, laboratory, computational and data oriented studies, all directed towards understanding the structure and physical processes in the earth’s interior, the crust or the earth’s fluid envelope.
Several members of Earth Physics have the recipients of major prizes in 2012. Dr. Andrew Hogg was awarded the 2012 Frederick White Prize for physical, terrestrial and planetary sciences; in August Dr. Michael Roderick was awarded the Dalton medal of the European Union of Geosciences for his ground breaking contributions in the areas of ecohydrology and remote sensing science; and in November Professor Kurt Lambeck was awarded the Balzan prize for his exceptional contributions to the understanding of the relationship between post-glacial rebound and sea level changes contributions. ANU staff excellence awards were received by Drs. Natalie Balfour and Michelle Salmon in Public Policy and Outreach for their contributions to the Australian Seismometer in Schools project, and Mr. Tony Beasely for excellence over 25 years of service.
Earth Physics staff were successful in applications for multiple ARC Discovery, during the year and Dr. Andrew Hogg was awarded an ARC Future Fellowship. Academic staff joining Earth Physics in 2012 were Dr. Sebastien Allgeyer in Seismology, Drs. Achraf Koulali and Lydie Lescarmontier in Geodesy and Drs. Andreas Klocker and Bishakhdutta Gayen in Geophysical Fluid Dynamics.
Ph.D. student T. Bodin, graduated and moved to a Miller research Fellowship at Univ. of Berkely, USA. Co-supervised Ph.D. student J. Stipcevic graduated and is now a postdoctoral fellow on an ARC Endeavour Scholarship. Ph.D. student Surya Pachhai is the recipient of the Paterson Scholarship.
During 2012, the Seismology group at RSES was heavily involved in both the acquisition of new portable seismic instrumentation and field campaigns to collect passive seismic data in various parts of Australia. Through AuScope AGOS, the seismology group is responsible for the construction of 250 new generation seismic recorders and the purchase of 20 deep sea Ocean Bottom Seismometers (OBS) for use by the Australian research community. In late 2012, the first 50 of the new generation recorders was completed and deployed in northeast New South Wales and southeast Queensland as part of the SQEAL1 array. SQEAL (South Queensland Eastern Australian Linkage) represents the next phase of the transportable seismic array experiment known as WOMBAT, which is run by the RSES seismology group and has grown to become the largest transportable array experiment in the southern hemisphere. Since 1998, a total of 15 separate array movements involving over 650 station locations has taken place, resulting in cumulative coverage of Tasmania, Victoria, New South Wales, southern Queensland and southern South Australia. Data from this experiment has helped transform our understanding of the deep structure and tectonic evolution of Phanerozoic Australia. Other fieldwork that has bee undertaken includes maintenance of the EAL3 array, which lies just south of SQEAL1, and maintenance of the BASS array between Tasmania and Victoria. The goal of BASS - a joint venture between RSES and the University of Tasmania - is to image the sedimentary and crustal structure beneath Bass Strait using ambient noise methods. An array of 24 broadband seismic stations was deployed on southern Victoria, northern Tasmania and several of the Bass Strait islands in late 2011, and will continue to operate until May 2013. In addition to ambient noise, teleseismic receiver functions and shear wave splitting techniques will be applied to improve our understanding of the tectonic relationship between Tasmania and mainland Australia.
In global seismological studies of the deep interior research has been ongoing in the area of structure and dynamics of the Earth’s inner core, the lowermost mantle and the lithosphere. With the recent expansion of global seismic data and the developments of new inversion techniques, the progress has been made in imaging and interpreting short scale structures in the inner core and the lowermost mantle. A project on the rotational dynamics of the inner core with respect to the mantle has been finalized, and a new project has been initiated in which array seismology is utilized to investigate a hemispheric dichotomy in inner core structure and to understand the nature of growth of the inner core (in collaboration with JAMSTEC, Japan and National Seoul University, Korea). International collaboration also includes a project on the multidisciplinary approach between seismology and mineral physics to understand inner core complex anisotropic structure (with University of Madrid). Partition modeling has also been applied to global dataset of seismic body waves sensitive to the lowermost mantle, and a new tomographic model of the lowermost mantle has been developed. Source physics and normal mode problems are being approached through partition modeling and these are now subjects of ongoing studies with PhD students.
In Geophysical Fluid Dynamics 2012 was the second year of operation of the ARC Centre of Excellence in Climate System Science, with one of its 5 university nodes in the Earth Physics area of RSES, focusing on ocean modelling. Research highlights included results from a suite of 'eddy permitting' to 'eddy resolving' simulations of the Southern Ocean. These showed that although the eddy field may strongly oppose any wind-induced increase in the transport in the Antarctic Circumpolar Current, the eddy compensation of the Southern Ocean overturning circulation is relatively weak, and therefore upwelling in the Southern Ocean may increase substantially under the enhanced westerly wind stress projected for the future. In other work, direct numerical simulation of a simple convection model was used to unravel the complex problem of kinetic and potential energy conversions when differential heating and cooling are applied to the ocean surface. Related solutions were also found from an ocean general circulation model applied to a simplified global ocean and analysed in terms of the energy conversions. It was concluded that surface wind stress and buoyancy forcing are likely to be of comparable importance in driving the overall global circulation and that there is an interesting coupling between the two forcing mechanisms. State-of-the-art numerical ocean model configurations were developed to resolve very small scales in the ocean, and these will be used to understand the role of these small scale processes in transporting tracers, such as heat and carbon dioxide, in the global ocean. A study of the interactions of turbulent mixing and convection using laboratory experiments, relevant to the deep overturning of the oceans, showed that convective overturning rates depend on the rates of mixing, as previously predicted, but also indicate that only the mixing rates in the upper ocean are of importance, in contrast to previous theories of deep circulation driven by abyssal mixing.
In Mathematical Geophysics research has been ongoing in the area of nonlinear inverse problems and development of new ensemble based approaches for seismic imaging and more general inference problems. In 2012 the focus has been on computational statistical approach to various data inference problems. The AuScope inversion laboratory saw much activity during the year with development of new codes for Bayesian regression and Partition modelling. This is a venture whereby scientific computer software is developed for the geoscience community implementing advance algorithms for nonlinear inversion applied to various data types. Several new projects were initiated during the year including studies on the inference of tectonic plate motion changes, reconstruction of the Australian Moho variability from multiple seismic datasets, and a collaboration with Earth environment staff on Uranium series dating in bones. Previous results on transdimensional inference algorithms were extended in collaboration with colleagues from Univ. of Rennes, France and Univ. of Berkeley, USA.
In lithosphere dynamics attention has been focused on tackling problems related to the strength of large-scale plate margins in a simple inverse fashion. Most of the strength of plate interfaces resides in the brittle regime, but estimates of the friction coefficient of tectonic margins are largely missing, and the few estimates available are incompatible with results from laboratory experiments. It has been found that the coefficient of friction of large-scale plate margins is more than one order of magnitude smaller than indicated by laboratory experiments. Further, its lateral variations are primarily controlled by the sediment intake of plate margins, which acts as a physical lubricant of the plate interface. These inferences have important implications for understanding the balance of lithosphere torques, as well as the stress-drop associated with seismic events.Geodynamics research activity has focused in 2012 on the use of satellite observations to study changes on Earth. This has included studies of the redistribution of water resources on Earth, developing more accurate methods for deriving height changes from satellite altimetry, studies of sea level variations around the Australian coastline and deformation of the Australian continent and Indonesia caused by earthquakes at the plate’s boundaries. The studies use a suite of different satellite missions including space gravity (GRACE), satellite altimetry (Cryosat II, Jason, Envisat), Interferometric Synthetic Aperture Radar and GPS. Estimates of changes in the Earth’s gravity field can now be made using in-house software to analyse the raw GRACE mission observations and a new website (grace.anu.edu.au) was developed to enable users to derive estimates of deformation and changes in water quantities using the GRACE satellites, providing the first such capability in Australia.
Professor Malcolm Sambridge