Where waters of different temperature (T) and salinity (S) lie close to each other in the oceans, there is frequently a region of relatively large lateral T and S gradients (a front). Mixing between the two masses of water is found to involve horizontal finger-like intrusions, often with many interleaved intrusions in a vertical stack. Thermohaline convection is a favoured driving mechanism for these intrusions, but the role of low-frequency internal inertia-gravity waves is unclear. The project will involve laboratory experiments designed to explore the possibility that waves may produce the intrusions and to examine the interactions of internal waves and thermohaline convection.

The oceans overturn, with surface waters sinking to deep in the ocean at high latitudes, drawing warm waters and heat poleward from low latitude. This flow and its transport of heat represents an important part of the climate system. The driving forces governing the overturning circulation, and its adjustment to changing boundary conditions associated with global warming, are controversial topics in oceanography and climate science. Global warming will cause more freshwater inflow from the melting of ice-caps at high latitude, and this might slow or even shut-down the ocean overturning. However, fundamentals of the dynamics are not understood. Laboratory experiments are being used to explore the convective circulation in simple cases. CFD simulations are being utilised in parallel with the experiments to further probe the dynamics. A PhD student with a physics or mathematics background will carry out laboratory fluid dynamics experiments or computational work with convection in a long rotating box forced by various distributions of heating and cooling on the base. The work will involve computer data logging, flow visualisation, and the analysis of the experimental data, from which we will learn about the physics underlying global ocean overturning.

Have you ever thought about how the oceans overturn, with surface waters sinking to deep in the ocean at high latitudes, drawing warm waters and heat poleward from low latitude? The driving forces governing this circulation, and the adjustment of the circulation to changing boundary conditions associated with global warming are controversial topics in oceanography and climate science. Global warming will cause more freshwater inflow from the melting of ice-caps at high latitude, and this might slow or even shut-down the ocean overturning. However fundamentals of the dynamics are not understood. Laboratory experiments are being used to explore the convective circulation in simple cases. An Honours or Masters student with a physics or mathematics background will carry out laboratory fluid dynamics experiments with convection in a long rotating box forced by various distributions of heating and cooling on the base. The work will involve computer data logging, flow visualisation, and the analysis of the experimental data, from which we will learn about the physics underlying global ocean overturning.

Have you ever thought about how the oceans overturn, with surface waters sinking to deep in the ocean at high latitudes, drawing warm waters and heat poleward from lowlatitude? Global warming will cause greater freshwater inflow at the sea surface from the melting of ice-caps at high latitude. This might slow, or even shut-down, the ocean overturning. In the geophysical fluid dynamics laboratory we are carrying out experiments with convection and rotation that explore the physics underlying global ocean overturning. A PhB scholar, research Intern, Summer Scholar or a student looking for a Special Research Topic, and who is studying physics or mathematics will assist with the laboratory fluid dynamics experiments, the computer logging of data, and the analysis of the experimental data.

Contact the supervisor directly for more information.

Water is a critical resource for Australia. We can't begin to manage properly what we don't monitor; therefore, monitoring the changes in water resources at local- and basin-scales is becoming increasingly important. The Gravity Recovery and Climate Experiment (GRACE) satellite gravity mission enables the possibility to measure basin-scale mass changes at monthly intervals, yet such capability is not being exploited to monitor Australia\'s water systems. Considerable research is required to determine the accuracy of the technique in the Australian environment where drainage basins are relatively small. This would involve the analysis and comparison of different international GRACE solutions and simulations for the Australian region to assess the achievable accuracy. The student would conduct an interesting scientific study that should lead to unique results pertinent to water resources in the Australian region.

Global warming is causing increased melting in polar regions. How do we know this? Because we can measure changes in mass balance (or the amount of ice that has melted) using space-geodetic techniques that detect variations in the Earth's gravity field and changes in ice height.
How fast are Antarctica and Greenland melting and how is such melting contributing to rising sea level?
There is the opportunity to study all aspects of the effects and ramifications of climate change, from measuring sea level variations using satellite altimetry and tide gauges, measuring with GPS the rebound of the Earth's crust caused by the melting of past ice sheets, monitoring mass balance changes through GRACE observations of gravity changes and/or assimilating all these observations to develop new models of past and present ice sheets for Greenland, Antarctica and North America. This exciting area of research has direct implications for understanding the present-day effects of climate change.

Signals transmitted from satellites orbiting the Earth are delayed as they pass through the troposphere of the Earth. This is measurable by GPS and so it is possible to measure how much water vapour is actually in the atmosphere using GPS. This is a new area of research that will involve the student learning about high-accuracy GPS analysis and modelling of the atmospheric effects. The map to the right shows the precipitable water vapour over the USA as estimated from GPS observations. Assimilating this information into weather forecasting and climate studies has not yet been attempted in Australia.

Contact the supervisor directly for more information.

Changes in atmospheric pressure cause elastic deformation of the surface of the Earth of up to 15 mm in height. The thermal variations of the atmosphere also cause atmospheric "tides" that produce periodic variations in atmospheric pressure - hence deformation - that are detectable in high-precision GPS analysis. The plot to the right shows the amplitude (in hPa) of the once/day pressure tide.

This project will involve generating new, more accurate models of the atmospheric tides for use in the analysis of GPS data, building upon recent advances of modelling the actual variations in atmospheric pressure. The student will be required to compute surface deformation from observed pressure data sets, integrate the new deformation models into the GPS analysis then (hopefully!) demonstrate from an analysis of GPS data that the new models yield improved results.

The 'solid' Earth actually deforms by up to 40 cm during the day as a result of the gravitational forces of the sun and the moon. Perhaps more surprising is that the continents also deflect because of the changing mass as the ocean tides move water around the surface of the Earth. The movement of the surface of the Earth can be measured by high-precision geodetic measurements of gravity and also position using gravimeters and GPS equipment. This project will involve using gravity and GPS observations at Mt Stromlo observatory to study the ocean tide loading effects in Canberra. The student/summer scholar will use the measurements to derive independent estimates of the tidal deformation, compare to existing global models and determine which - if any - of the existing models are accurate.

The project will involve learning how to compute accurate GPS coordinates, how to reduce gravity measurements and how to model tidal deformation. Computing skills are not required, although would be very useful!

Very Long Baseline Interferometry (VLBI) involves observing radio sources with astronomy telescopes, from which very accurate estimates of distances between telescopes and estimates of Earth rotation can be made. Recently, a software program was developed at Swinburne University (Victoria) to correlate astronomic VLBI observations - which is a very significant improvement over convential correlation and provides Australian researchers with considerable independence. This PhD program will involve continuing the development of the software correlator so that it can be applied to geodetic VLBI observations as well. Once this can be done, exciting new opportunities will become available - such as observing GPS satellites using VLBI instruments, analysing for the first time the data from the new VLBI installations in Western Australia and the Northern Territory (to be commissioned in 2008). The student will be involved in developing and enhancing software, analysing VLBI data and integrating the VLBI observations to GPS satellites into existing geodetic software packages. The student will be supervised jointly by Steven Tingay (Swinburn) and Paul Tregoning (ANU).

We don't know yet what new results such research is going to uncover ...... come and find out!

Papua New Guinea is one of the most active tectonic regions of the world, with every possible type of plate boundary, dozens of active faults and several major earthquakes occurring every year. Measurement of ground movement from GPS observationscan tell us about deformation, strain caused by locked faults etc. Estimating earthquake locations can identify faults and explain the observed deformations. There are numerous research projects available using earthquakes and/or geodetic data to study how the Earth moves in Papua New Guinea.

Contact the supervisor directly for more information.

Seismic tomography is widely used to image 2-D and 3-D Earth structure at a variety of scales. In principle, it is similar to medical tomography (CT scan), in that it uses the constraints imposed by a multitude of crossing paths to construct an image. However, instead of using X-rays, seismic waves from artificial (e.g. explosions) or natural (e.g. earthquakes) sources are used. In addition to the challenges of achieving good path coverage in the Earth, a further complication is that seismic tomography, unlike its medical counterpart, is a non-linear problem. This is because path trajectory varies in response to changes in seismic wavespeed. Conventional seismic tomography schemes either assume that the problem is linear, or can be solved using iterative non-linear methods; neither assumption is valid in strongly heterogeneous media.

The aim of this project is to compare the results of iterative non-linear and fully non-linear tomography for a variety of datasets. A recently developed scheme known as the Fast Marching Method or FMM will be used to solve the forward problem of data prediction; gradient based inversion schemes will be used to solve the iterative non-linear problem; and the Neighbourhood algorithm will be used to solve the fully non-linear problem. Possible lines of investigation include: at what level of model complexity do the iterative schemes break down; does the fully non-linear scheme always produce superior results; at what point does the fully non-linear scheme become computationally impractical; how do the schemes differ in their ability to assess solution non-uniqueness? The requirements for undertaking this project include familiarity with UNIX/Linux, some programming experience, and a background in physics, mathematics or geophysics.

Contact the supervisor directly for more information.

In recent times, tomographic imaging techniques have enabled seismologists to produce detailed three-dimensional maps of Earth structure from large seismic datasets. Traditional methods of seismic tomography often rely on iterative non-linear inversion schemes and represent structure by a regular grid of parameters. However, iterative inversion schemes may converge to local minima and regular parameterizations are inconsistent with non-uniform distributions of data. The aim of this project is to introduce a suite of new computational tools to seismic tomography in order to overcome these problems. The important requirement of defining a continuous medium from an irregular distribution of nodes placed only where they are required by the data can be satisfied using natural neighbour interpolation. We envisage the use of a fully non-linear search technique to solve the inverse problem, e.g. the locally developed neighbourhood algorithm. Finally, the forward problem of calculating model predictions can be rapidly solved using grid-based wavefront tracking schemes such as the fast marching method. The use of direct search methods in seismic tomography is computationally expensive, but the project will have ready access to a powerful 128-node supercomputer. A background in computational mathematics is recommended.

Contact the supervisor directly for more information.

The last 20 years has seen a huge impact from seismic imaging studies across many areas of geophysics. The figure opposite shows results from 3-D tomography for lateral variations in the Earth's bulk sound speed, carried out by members of the seismology group at RSES.

Projects are available in both developing and applying seismic inversion techniques across regional and global scales. These studies often involve large travel time or waveform data bases and require the use of sophistical data analysis techniques, computational mathematics, and advanced visualization tools. Projects are scaled to fit the degree type being undertaken by the student. Appropriate backgrounds include Physics, Mathematics, Geophysics, Computer Science or any degree with a substantial component of these fields.

Contact the supervisor directly for more information.

The computational simulation of seismic waves through a complex Earth model is a major focus of seismology research. These calculations have application across many distance scales from that of exploration geophysics to whole earth seismic structure (see below). The current forefront is solving the elastic wave equation in complex 3-D geometries. The figure opposite shows the results of ray tracing calculations for wavefronts through a complex 2-D structure. A new challenge in geophysics is to perform inversion of complete seismic waveforms for earth structure and source characterization over regional and global scales.
Projects are available in various aspects of theoretical seismology, including methods for wave propagation and inversion. Current interests are in the development to new approaches to wavefield simulation, and multi-phase wavefront tracking in 3-D. Projects are scaled to fit the appropriate degree being undertaken by the student. A background in Physics, mathematics, geophysics, computational science or engineering would be needed to undertake a project in this area.

Contact the supervisor directly for more information.

All of our observations that constrain the Earth's interior structure are made at the surface. Hence there is always an `inverse problem' in making use of indirect observations to perform inferences about the Earth at depth. Inverse problems occur in many areas of the Physical sciences, and it is the subject of on going research of how best to solve them. In Geophysics many inverse problems are nonlinear, for example using seismic waveforms or travel times of waves to constrain the structure at depth. Recent research in the seismology group has led to a new fully nonlinear approach to certain types of inverse problem. The figure opposite shows some results. Each point represents an earth model colour code by fit to data. The cross shows the model with best data fit. Projects are available in the study of nonlinear inverse problems and methods for their solution. Questions include: How do we best parametrize an inverse problem ? How do efficiently search large dimensional parameter spaces ? How do we handle severe nonlinearity ? Projects are likely to involve a combination of mathematics, advanced computation, and physics applied to a particular geophysical inverse problem. For more information on parameter search look here.

Contact the supervisor directly for more information.

In an exciting proposal currently under development we plan to model the energetics of dislocation migration in crystals, and to measure the impact of such stress-induced dislocation migration on viscoelastic behaviour through mechanical testing in torsional forced oscillation. The project will focus on MgO - on account of its structural simplicity and ready availability as large single crystals. The project will involve a mixture of computer modelling (ab initio/ atomistic simulation of dislocations – through international collaboration with Andrew Walker (University College, London) and Patrick Cordier (University of Lille, France), experimental deformation by dislocation creep, characterisation of defect microstructures by electron microscopy, and the development of improved techniques for mechanical testing though low-amplitude torsional oscillation (Jackson & Fitz Gerald). There is scope for student involvement in both the computer simulation and experimental rock physics aspects of the project.

The emerging capability of our ANU Rock Physics laboratory for the testing of cylindrical rock specimens in both flexural and torsional oscillation provides an exciting opportunity to study the partial relaxation of the bulk modulus (incompressibility) associated with phase transformations that involve a volume change. In partially molten upper-mantle materials the small melt fraction is typically accommodated within a network of interconnected grain-edge tubes of triangular cross-section as shown in the picture. The student would be involved in the preparation of suitable synthetic rock specimens and their mechanical testing with flexural oscillation methods in search of the modulus relaxation and dissipation associated with reversible stress-induced melting/crystallisation in such partially molten material. The findings will help with the interpretation of seismological compressional wave speed/attenuation models for the Earth’s upper mantle. The project involves international collaboration with Prof. Uli Faul of Boston University.

Fluids are expected to profoundly modify the seismic properties of the cracked rocks of the Earths upper crust but so far there are few relevant laboratory measurements. With funding from the Australian Research Council we are developing novel experimental techniques to build a better laboratory-based understanding of the seismic properties of fluid-saturated crustal rocks. The outcome will be an improved capacity to monitor the presence of fluids in diverse situations ranging from geothermal power generation and waste disposal to upper-crustal fault zones. This project involves international collaboration with the research group led by Professor Douglas Schmitt at the University of Alberta (Canada). There are exciting opportunities for the participation of students in (i) establishing procedures for measurement of seismic properties through low-frequency forced flexural oscillation of cylindrical rock specimens; (ii) undertaking exploratory measurements in torsional and flexural oscillation of suitable cracked media (pictured) with fluid saturants of contrasting viscosity; and (iii) performing complementary measurements with high-frequency ultrasonic and low-frequency forced-oscillation methods.

Unique equipment for low-frequency laboratory measurement of seismic wave speeds and attenuation has recently provided new insights into the frequency, temperature and grainsize sensitivity of seismic wave speeds and attenuation in fine-grained synthetic specimens of the dominant upper-mantle mineral olivine. The possible role of crystal defects known as dislocations in seismic-wave attenuation is the focus of the current Ph. D. project of Robert Farla. The next exciting frontier is the possible enhancement of such non-elastic effects by small amounts of water accommodated as defects within the olivine crystal structure. This work, being undertaken in collaboration with Professor Uli Faul of Boston University (BU) provides opportunities for students to work at both ANU and BU on the preparation, characterisation and mechanical testing of such materials and the development of strategies for modelling and seismological application of the results.

A new approach for the internally consistent modelling of the equation-of state and elastic properties of minerals under the extreme pressure-temperature conditions promises to revolutionise the interpretation of seismological models for the Earth’s interior. The new method has recently been bench-tested on a diverse range of experimental data for magnesium oxide (Kennett & Jackson, Phys. Earth. Planet. Interiors, 2009). Now, there is an opportunity for the involvement of a Ph. B. / Honours/ M. Sc. student in the systematic application of this approach to experimental data, including local measurements of the pressure and temperature dependence of elastic wave speeds, for the upper-mantle mineral olivine and its high-pressure polymorphs wadsleyite and ringwoodite.

Improved structural models of the Earth and the knowledge about seismic wave propagation allow seismologists to study earthquake mechanisms. The earthquakes could most generally be divided to tectonic and volcanic. The far-field radiation of most tectonic earthquakes can be conveniently described with the so-called double-couple system of forces. However, a full seismic moment tensor representation is more complete form of the mathematical representation of seismic sources, especially in non-tectonic environments. Of particular interest are seismic events with anomalous seismic radiation and puzzling focal mechanisms, such as volcanic earthquakes, mid-ocean ridge events or explosions.Different computational methods are used to reveal statistically significant non-double-couple components of the moment tensor and model complex finite sources. A student with maths and physics background and strong analytical skills is invited to join the project and assist with analysis and interpretation of results. Please contact the supervisor directly at hrvoje@rses.anu.edu.au for more information.

We live in a decade of unprecedented quantity and quality of seismic data, which are easily accessible online. Although the quality of seismic records is improving constantly, there are still vast amounts of unanalysed seismic waveforms, which might hold a key to deciphering unresolved geophysical puzzles. One such puzzle is the inner core structure. The inner core was discovered in 1936, and inner core anisotropy (directional dependence of elastic properties) was hypothesised fifty years later, to explain anomalous travel times of core-sensitive seismic waves. Some recent results suggest the existence of "innermost inner core". However, inadequate spatial sampling of the central inner core by seismic waves makes further advances on this topic very challenging. This project will focus on finding new ways of sampling the centre of the Earth and interpreting the results in the context of our planet's dynamics and evolution. Interested students with a physics or maths background are invited to contact the supervisor directly at hrvoje@rses.anu.edu.au to discuss possibilities.

Seismologists combine the so-called receiver functions and surface wave data to improve the general understanding of crustal and upper mantle structure in various regions of the world. An important humanitarian objective of obtaining improved structural models is better understanding of the seismicity and hazard assessment for the region of study. Receiver functions are mostly sensitive to sharp gradients in Earth's elastic properties (such as the Moho discontinuity), while surface wave data contribute to a better understanding of overall seismic wave speeds. We are working to develop a reliable method for the joint modeling of these two types of data, possibly with independent information from seismic "noise". This project will focus on applying this method to the data collected by the seismic stations at various regions to better constrain crustal and upper mantle structure, including features such as the crustal thickness, upper mantle low-velocity zone and transverse isotropy (polarization anisotropy). Students with a strong computer science, physics or mathematics background including familiarity with Unix are invited to contact the supervisor at hrvoje@rses.anu.edu.au for more information.

This topic is a subject of very active research in the geophysical community and was exploited in a recent science-fiction motion picture 'The Core' (although the scientific facts in the movie were almost entirely wrongly represented). Differential rotation of the inner core with respect to the rest of the planet was first suggested from numerical simulations of the geodynamo in 1995. Since then, seismological studies aiming to detect differential rotation of the inner core using temporal changes in seismic waveforms were mostly controversial, and often subjected to criticism (the title above was taken from a publication in Science). One reason for scrutinising seismological data is a very likely inadequate resolution to resolve small temporal changes in inner core properties. This project will explore a unique dataset from Australian seismic stations to address the above issue. A highly motivated student with a background in geophysics, physics, astronomy or mathematics will find the project challenging and satisfying. Please contact the supervisor directly at hrvoje@rses.anu.edu.au for more information.

The aim is examine fault rocks produced in some of the Earth's most famous faults, for example a sample from the EarthScope project that has drilled through the San Andreas fault at some km depth, or samples from some of the most famous so-called "impossible" detachment faults, namely those that appear to form at low-angles over large areas in extensional environments. How can we predict earthquakes if we don't know how the rock in the fault itself is behaving? How can we say that LANFs are impossible if we do not understand the processes that operate within them? Photo adjacent shows the Whipple detachment fault, a low-angle fault that formed when western North America was pulled out from underneath the Colorado Plateau. We want to understand why such a big fault could be so sharp, for example. Is there evidence for sub-critical propagation of fractures? If we can demonstrate this we come closer to understanding one of the most puzzling riddles that has confronted modern Earth Sciences. There is some room to shape this project differently for a geology major as opposed to a physics or geophysics major (e.g. in respect to fieldwork).

Mantle plumes carry heat upwards from a thermal boundary layer at the bottom of the mantle, and the thermal boundary layer is formed by heat conducting out of the core. Plumes thus help to cool the core. The efficiency with which plumes remove heat is debated and needs to be clarified. The project would be to use an existing numerical code to explore different parameters that control the plume and to compare the resulting plume with observational constraints. Some programming experience would be required.

The so-called maximum entropy production principle is a relatively new idea that may apply to fairly complex dynamical systems. The project would be to test the MEP principle by developing applications to some of Earth's internal processes and comparing its predictions with progressively more sophisticated numerical models. Potential applications are the compositional-dynamical stratification of the mantle and the energy involved with core convection and the dynamo mechanism of Earth's magnetic field. Good computational skills would be required.

The physics of thermal mantle plumes is quite well understood, and they provide a good explanation for volcanic centers like Hawaii and Iceland, and for the chains of extinct volcanos that extend away from these 'hotspot' sites. They also seem to explain gigantic flood basalt eruptions that occur once every 10-20 Ma. However there is a range of other volcanism that doesn't fit the classic pattern of flood basalts and related hotspot tracks. Plumes may entrain some denser material from the bottom of the mantle, and then their dynamics would be more complicated. These dynamics would be explored with numerical models in two and three dimensions. The results would have implications for the tectonic evolution of the continents and for the cooling of the core and the history of the dynamo. Good computational skills would be required.

This project continues numerical modelling of mantle dynamics in two and three dimensions to explore models that can accommodate geophysical, geochemical and tectonic constraints. We have a fairly clear understanding of how plate tectonics, mantle convection and mantle plumes work at present, but we would like to know how the dynamics of the mantle system has changed as Earth has slowly cooled over the past 4.5 Ga. There is geochemical and isotopic information from the mantle that has been difficult to reconcile with dynamical modelling. The chronology and tectonic history of the continental crust also provides important constraints, especially since they indicate the system has had episodes of heightened activity. Good computational skills would be required.

The South Pacific is characterized by the presence of several hotspots and a superswell. Seismic attenuation measurements are more sensitive to variation of temperature than seismic velocities, due to the strong dependence of attenuation to temperature. French Polynesia, East and North of Australia are ideally located to perform measurements of attenuation from multiple ScS waves. The student will measure seismic attenuation using a stacking procedure for the multiple ScS spectra, using data already available from both the RSES database for Australia and from the PLUME (Polynesian Lithosphere and Upper Mantle Experiment) network for French Polynesia (collaboration with Dr. G. Barruol, CNRS, France). The goal will be to produce maps of the patterns of seismic attenuation in the mantle. The measurements will give important constraints on the temperature variation in the South Pacific upper mantle. More details can be found by contacting the supervisors.

An enthusiastic and capable intern could become involved in the development and application of methods for display and analysis of seismograms to exploit 3-component recording of vector ground motion. The work would include the software implementation of published algorithms, their application, and the development of new techniques.

A programme of temporary broad-band seismic deployments throughout Australian Antarctic Territory took place during austral summers between 2002-2005. These stations recorded energy from distant earthquakes which sample the crust and upper mantle beneath the ice of East Antarctica, currently the least explored part of the tectonic Earth. Seismic structure will be determined from travel-time, receiver function and tomographic analyses of the data towards a better understanding of the tectonic structure and history of East Antarctica.



Research student(s) working on the project would have the opportunity to take part in fieldwork deployments in Australia and possibly Antarctica, use existing data collected by the RSES Seismology group, develop seismological methods and use potential field and geological data in working towards their final tectonic interpretations.

Energy from distant earthquakes, from the southwest Pacific and other regions, samples the upper-mantle and crust beneath East Australia and New Zealand and is being recorded at dense arrays of 3-component seismic stations enabling the seismic structure in the lithosphere to be resolved in new detail. Tomographic and receiver function methods will be used to address the terrane architecture and tectonic history of East Australia.

Research student(s) working on the project would have the opportunity to take part in field deployments in East Australia and possibly New Zealand, use existing data collected by the RSES Seismology group, develop seismological methods and use magnetic, gravity and geological data in their final interpretations.