The chemistry of earthquake rupture

Earthquakes are among the most disastrous natural events, claiming, in the last three decades alone, several hundreds of thousands victims and $500 billion in economic losses. Earthquakes result from the sudden release of tectonic stress which builds up in the relatively brittle rocks of the upper crust. In the deeper crust (generally >15km) rocks are more plastic and less prone to sudden, seismic brittle failure. However, even in the upper crust faults can move aseismically (creep), depending on the combination of temperature, pressure and fluids which affect the frictional behaviour of fault materials, and on how recently the fault has been sliding.
By experimenting on synthetic and natural fault materials, Earth scientists have learned much about the restrengthening of fault zones after earthquake rupture, the strength profiles of different fault materials, their ability to promote or arrest failure, and the importance of the permeability of fault rocks. Aqueous fluids are paramount in modulating the earthquake cycle and rupture; their role has been deliberated in the past decades, devoting particular attention to the restrengthening and alteration of material properties (Evans et al., 1995; Boulton et al., 2012; Wästeby et al., 2014; Boulton et al., 2017), the pressure cycling during earthquake nucleation (Blanpied et al., 1992), the thermal pressurisation due to frictional heating (Wibberley and Shimamoto, 2005), and the redistribution of heat in the crust surrounding fault zones (Wang et al., 2013; Sutherland et al., 2017; Coussens et al., 2018). In spite of these pioneering studies, many aspects are poorly understood. For example, it is not clear how the chemical reactions that take place through the earthquake cycle can affect the fault behaviour, what is the fluid's role in sealing the fault zone, and how subtle changes in the regional chemistry may reveal fault activity.
This project will investigate and characterise co-seismic chemical reactions that modulate pore fluid chemistry and mineralogy of fault zones. Rocks will be experimentally faulted in contact with a hydrothermal fluid to interrogate co-seismic chemical reactions. Fluid and rock samples will be geochemically characterised prior to, and after experimental work to identify mineralogical and chemical changes that occur during simulated earthquake slip under different conditions. These changes will then be related to variability measured in the fluid permeability, mechanical and frictional properties of the investigated materials to identify the chemical reactions that occur and their control on earthquake rupture and propagation processes. Such work coupling geochemical analyses of simulated fluids and rocks during simulated earthquake slip has only been documented in few instances to date (Violay et al. 2012).