The structure and physical properties of faults
Dan Faulkner, Elisabetta Mariani, Rachael Bullock, Christina Kelly, Janine Kavanagh (Volcanology), Andreas Rietbrock (Seismology), Carolyn Boulton, Michael Allen, Elliot Wood
Faults occupy a small fraction of the Earth’s crust but exert a strong influence on its properties. Brittle faulting produces pathways or barriers to fluid flow, waveguides or reflectors for seismic wave propagation, and a limit for the strength of the upper crust. We have studied the internal structure of many major faults around the world including the Carboneras Fault in Spain, the Atacama Fault in Chile, the Karakoram Fault in India and the Alpine Fault in New Zealand. These studies have led to a change in our understanding of how fault structure might influence the mechanics of faults, how the growth of fault damage zones occurs and how faults are imaged seismically.
The mechanics of earthquakes and faulting
Dan Faulkner, Rachael Bullock, Ben Edwards (Seismology), Sabine den Hartog, Carolyn Boulton, Catalina Sanchez
Fault produce a wide range of slip behaviour, from earthquakes to fault creep. Understanding what physical conditions or mineralogy dictates different modes of fault slip and the strength of faults is a key objective. Moreover, the character of seismic slip must be understood in order to predict the resultant radiated wavefield, which can then lead to better probabilistic seismic hazard assessment. We conduct experiments to investigate the fundamental physics of fault slip, from nanometres per second (plate motion rates) to several metres per second (earthquake slip rates).
The dynamics and mechanics of dehydrating systems
Dan Faulkner, John Wheeler, Elisabetta Mariani, Henri Leclere, John Bedford
Dehydration reactions affect subduction zone seismicity. The interplay between deformation, permeability, mechanics, and reaction kinetics is key to these processes but is poorly understood. We use high-pressure, high-temperature experiments to simulate the conditions of dehydrating systems under stress so that we might better understand them. We use novel microstructural techniques such as 4D high-resolution X-ray tomography to image the progress of reactions (in collaboration with the Advanced Photon Source at the Argonne National Laboratory, Illinois).
Interactions of stress, metamorphism and fluid flow in the Earth
John Wheeler, Dan Faulkner, Elisabetta Mariani, Henri Leclere, John Bedford, Joe Gardner
Heating and dehydration of minerals creates fluids which, if at high pressure in pores, can trigger earthquakes in a stressed region. However, fluid pressure and stress influence reaction rates and consequently there are feedbacks in the behaviour which must be understood to underpin our interpretations of minerals in deformed rocks and our predictions of fluid pressure evolution and flow. In research using gypsum as an analogue for silicates and their dehydration, Henri Leclere together with John Wheeler, Dan Faulkner and Betty Mariani use experiments, quantitative analysis and numerical models to constrain these feedbacks. Closely linked to this research is detailed analysis of the deformation mechanism of “diffusion creep”, in which applied stress induces chemical diffusion and hence shape change. New numerical models developed by John Wheeler are changing the ways we understand this mechanism in terms of rheological and seismic anisotropy, and hence how we interpret the deep Earth where this deformation mechanism may prevail.
Properties of shear zones and fluid-rock interactions
Elisabetta Mariani, John Wheeler,Dan Faulkner, Joe Gardner, Joe Aslin
The Earth’s crust deforms under applied stresses that drive plate tectonics. At depths of 10 km and deeper, large strains are localized into brittle-viscous and viscous shear zones. We study a range of regional scale exhumed shear zones such as the Cossato-Mergozzo-Brissago and Pogallo Lines and the Gressoney shear zone in NW Italy, and the Alpine Fault zone in New Zealand South Island.
Quantitative microstructural characterization of constituent minerals in shear zones enables us to improve our understanding of the deformation mechanisms that are dominant in nature. Also, little is known on mechanisms of fluid transport at depth therefore we study hydrous minerals such as phyllosilicates and amphiboles and other “nominally anhydrous” minerals to gain insight into fluid-rock interactions, the fluid budget and fluid transport in shear zones.
CO2 capture and storage
Dan Faulkner, Richard Worden (Diagenesis)
A key component of successful CO2 storage in sub-surface reservoirs is the integrity of the caprock that must act as an effective long-term seal. We investigate the properties of typical caprocks under the conditions found at reservoir conditions and how they evolve under the changing physical and chemical conditions that exist during injection and storage of CO2.
The geomechanics of geothermal systems
Dan Faulkner, Yan Lavallee, Aurelio Melia, David McNamara (GNS, New Zealand)
Geothermal energy relies on permeable networks through hot rocks. We study the geology of the geothermal fields and quantify the properties of rocks found in New Zealand geothermal reservoirs such as strength, elasticity and permeability in order to understand how to ensure long-term viability of these fields.
The rheology of mantle materials (Mariani and Wheeler)
Elisabetta Mariani, John Wheeler, Tom Garth, Pam Kaercher, Jacob Tielke, Chris Gregson
The internal behaviour of planet Earth is dominated by mantle convection. We measure the rheology of upper mantle minerals and lower mantle mineral analogs so to provide the constraints needed for a fuller understanding of the viscosity contrast between the upper and lower mantles. The cycle of volatiles on Earth, particularly water, exerts controls on a variety of processes, from the initiation and evolution of life, to earthquakes and the deformation of the Earth’s crust, to the viscous flow of mantle mineral assemblages. So we investigate the feedback between volatile fluxes and mantle dynamics through time by quantifying the rheology of “nominally dry” upper mantle minerals that contain intracrystalline water, such as olivine and pyroxenes.
Elisabetta Mariani, John Wheeler, Alan Boyle, Pam Kaercher, Michael Allen, Joe Gardner, Joe Aslin
We work at the forefront of electron backscatter diffraction (EBSD) techniques in the SEM contributing to cutting edge developments in data acquisition and data processing. The simultaneous acquisition of EBSD and energy dispersive spectroscopy (EDS) data allow us to quantify the absolute crystallographic orientation and mineralogy of Earth’s materials. We are currently developing new solutions to pseudosymmetry problems in perovskites and other structures. In our research we bridge space and time scale gaps by combining quantitative EBSD-SEM techniques with fieldwork, rock deformation experiments and modelling.