Slip behaviour at and around faults has been shown to be highly dynamic with variability in behaviour occurring both spatially and temporally. This exciting project explores the underlying physical processes that lie at the core of dynamic slip behaviour by probing the rock record of fault slip. In this novel project, you will integrate knowledge obtained from high resolution laser scanning (LiDAR), quantitative microstructural work, and Quaternary fault studies to gain an in-depth understanding of the physical processes acting on a fault and/or fault zone. Results will be far reaching in fundamental science with direct implications for applied science in terms of earthquake hazard evaluation and forcasting.
Earthquakes are one of the main hazards that humanity faces, therefore improving our ability to anticipate how fault zones behave through time is of major importance. However, we have still very little understanding of why some faults appear to accommodate different slip modes and others do not, how different slip processes are represented in the rock record, and why faults cycle between different modes. This project in novel in its cross-disciplinary nature. The project builds on existing earthquake cycle analysis in terms fault history determined by isotopic age dating on fault rocks, patterns of fault surface roughness, and their link to microstructures from natural and experimental fault rocks. In Leeds we have the rare opportunity for this integration as experts in the respective fields are within the same University. In addition, the highly specialized experimental and analytical equipment exists in house, making this challenging project possible. This project is further strengthened by the strong personal and scientific links between the Leeds team and the project collaborator.
In this project, the student will work with leading scientists at Leeds (Sandra Piazolo, Laura Gregory and Ali Ghanbarzadeh), and Durham (Ken McCaffrey) to integrate the latest techniques in characterising fault zone structures in order to understand the dynamics of the physical processes preserved from the earthquake cycle. The project will address the following questions:
1) Processes: What physiochemical processes are involved in fast fault slip, creep, and postseismic afterslip? How do these processes evolve as a fault grows and develops?
2) Recognition: How can various earthquake cycle behaviour be identified in natural rocks? What is the link between micro- and meso- scale features of damage on a fault, if any?
3) Effect: What is the mechanical effect of the different processes identified in (1)? What is an appropriate mathematical representation of such dynamic behaviour? This mathematical description will form the foundation to improve the timescale and spatial behaviour of fault zones past, present and future?
In order to answers the question posed above, it will be necessary to combine different techniques and approaches.
1. Investigate small scale features in samples close to or on the fault using the latest field based (e.g. fault zone laser scanning) and analytical (e.g. nanoscale electron microscopy, microtomography) techniques. The field area in central Italy with faults of known Quaternary fault slip rates (e.g. Cowie et al. 2017) will be the initial focus but we anticipate expansion of the field area to southwestern Turkey and/or the western USA.
2. Conduct experiments using novel experimental designs (e.g. modified Universal Material Tester-UMT) allowing for direct shear experiments with high frequency cycles that can directly measure tangential loads and frictional behaviour in-situ while varying the normal force. Chemical fingerprinting will allow recognition of the sequence of “events”.
3. Analysis of experimental samples before and after experiments using high-end microscopy including an unique Focussed Ion Beam Scanning Electron Microscope with time of flight spectrometer and Electron backscatter diffraction detectors). Analysis will be from the nanometer-scale, to the micron and to mm scale. Analytical results from experiments will be compared to natural rocks from geological faults.
4. Develop and test hypotheses linking the observations from the rock record into fault slip behaviours, relying on what we already know from the earthquake and Quaternary records on the faults you have studied.
We expect the balance between these approaches to vary depending on the specific interests of the student. There is the potential to develop novel methods of integrating what you may observe in the rock record with physical models of fault slip; a challenging but important endeavour.
Potential for high impact outcome
The project sits in an emerging research field with important fundamental research to be done but also important societal implications. Research outcomes will be a step-change in the science underpinning prediction and assessment of fault rock behaviour with large impact. Consequently, we anticipate the project will generate several international publications in high impact journals.
Training
You will be part of an active group of researchers and students at SEE that focus on earthquake dynamics and advance microstructural analysis including experts in active faulting and microstructural investigation of rocks and minerals. In addition, the student will be able to join the Institute for Functional Surfaces at School of Mechanical Engineering, a world class research institute focussed on surface chemistry and deformation. This project provides a high level of specialist scientific training in: (i) geological field skills, (ii) laboratory analysis including state-of-the-art microstructural and –chemical analysis (from outcrop to nanometer scale) (iv) data processing and interpretation of laser scanner data and (vi) deformation experiment with and without fluids using an unique tribology rig available. Microscale analysis will be using the most advanced analytical suite currently available in the UK housed in the new Bragg Centre (https://www.leeds.ac.uk/info/130565/bragg_centre_for_materials_research), University of Leeds.
Student profile
The student should have a strong interest in active tectonics challenges, a desire to undertake laboratory and fieldwork overseas, and a strong background in a quantitative science (earth sciences, geophysics, geology, physics, natural sciences). Willingness and excitement for taking up the challenge to work at the boundary of earth science, mechanics and microstructural analysis utilizing a combination of technique (field analysis, in-depth microstructural analysis, and experiments) is a prerequisite. This is a multidisciplinary project but we welcome students with enthusiasm for any relevant field as the project is flexible based on your interests.
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