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Elasticity of geological and planetary materials using novel X-ray imaging


School of Earth Sciences

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Dr Andrew Thomson , Prof J Brodholt Applications accepted all year round

About the Project

The structure and composition of the Earth’s deep interior cannot be directly measured, but instead must be inferred from seismic velocity data generated by Earthquakes. However, this approach relies entirely on the availability of high-quality data for the seismic properties of all potential deep Earth minerals. Moreover, these properties must be known as a function of pressure, temperature and composition. Despite their fundamental importance for understanding the basic properties of the deep Earth, there are very few measurements of seismic velocities of minerals at the pressure and temperature conditions of the deep Earth, and so we have to rely on large extrapolations of low pressure and temperature data, or on theoretical estimates.

This PhD studentship, fully-funded for UK students by UCL/AWE, will aim extend our recently developed technique for measuring the seismic velocities (compressional and shear velocities) of Earth and planetary materials at high pressure and high temperature conditions [1]. In these experiments high-frequency sound pulses are passed into high-pressure samples contained within a Paris-Edinburgh press. By measuring the time-delays between echoes returning from the top and bottom of the sample, whilst simultaneously measuring the sample’s length using X-rays, velocities can be determined very precisely [2]. The novel aspect of this project is the lab-based approach to sample X-ray imaging, which we believe is globally unique. Measurements can be performed at upper mantle conditions extending to > 20 GPa and 2000 K, which makes the scope for this technique extremely broad and exciting.

It is intended that the PhD project will focus on measuring the acoustic wave velocities of (i) hydrous silicate phases that are stable in the subduction factory and are important components of the deep Earth water cycle and (ii) metallic alloys that are relevant to understanding the composition and behaviour of small planetary cores. However, potential applicants who have an interest in studying the thermoelastic properties of alternative Earth, planetary or technological materials are encouraged to discuss these with the supervising team. Data collected will be fitted and analysed using thermoelastic equations of state, ensuring that it is efficiently disseminated and available for incorporation within future mineralogical planetary modelling projects or other relevant datasets. The PhD will provide full training and experience in high-pressure experimental techniques, X-ray imaging and diffraction alongside relevant coding and data analysis skills. As the project is co-funded by AWE, the student will also have opportunities to gain experience of an industry research perspective, alongside the academic environment at UCL. Finally, there is additional scope for performing some experiments at national facility laboratories in the UK, Europe and Japan.

Funding Notes

This project is fully funded for UK applicants as a UCL Impact Studentship in collaboration with AWE, and includes an annual tax-free stipend at the normal RCUK rate (£17,428 in 2020/21).

Applicants require to have (by the time of starting) a Masters level degree (either undergraduate or postgraduate) in Geology, Geophysics, Physics, Material Sciences or a closely related field and an enthusiasm to work in a lab-based setting. Some knowledge of computer programming in Matlab/Python or a similar language would be highly beneficial.

References

[1] Thomson, A.R., et al. (2019) Seismic velocities of CaSiO3 perovskite can explain LLSVPs in Earth’s lower mantle. Nature, 572, 643–647.

[2] Li, B., and Liebermann, R.C. (2014) Study of the Earth’s interior using measurements of sound velocities in minerals by ultrasonic interferometry. Physics of the Earth and Planetary Interiors, 233, 135–153.
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