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.