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.

The Indian Ocean Dipole is now recognised as a climate system of international importance because of its effect on rainfall in Indonesia, Australia, Asia, and East Africa. Resolving the debate about how the Dipole and ENSO climate systems interact, and how they respond to different background climates, is essential for understanding the nature of drought in southern Australasia. Would you like to work with an international team to build on advances made at RSES in the microanalysis of stable-isotopes and trace elements in recently discovered corals from the Mentawai Islands, Sumatra, in western Indonesia? Corals from the Mentawai Islands are well located to quantify the range of IOD variability during times when Earth's climate was different from the present day. You will also have the special opportunity to answer a pressing question in the collective mind of Australasian society, how often do great-earthquakes occur and where will one strike next? The nature of great compound earthquakes, such the Boxing Day 2004 / Easter Monday 2005 event in Sumatra, is poorly understood, largely because the regularity of catastrophic earthquakes in space and time remains unanswered. This facet of the project will develop geochemical tracers in corals to reconstruct the recurrence intervals of great submarine earthquakes and tsunamis in Australasia. You will join an experienced international team from Australia (ANU, AIMS, CSIRO), Indonesia (LIPI), and the USA (Caltech, U. Wisconsin) who have complementary skills in geochemistry, geochronology, palaeoclimatology, ocean-atmosphere dynamics, palaeoclimate modelling, and palaeoseismology. The ideal candidate will enjoy fieldwork on the coral reefs of Indonesia (mapping, surveying, coral drilling, water sampling) and the development / application of innovative laboratory techniques. Contact Dr Mike Gagan (Michael.Gagan@anu.edu.au) and Dr Linda Ayliffe (Linda.Ayliffe@anu.edu.au) for further 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).

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.