Feedbacks between faulting and fluid flow throughout the seismic cycle: An experimental approach

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In the Earth's crust, fluids are ubiquitous in the pores and cracks present in rocks. In tectonically active areas, for instance along major crustal faults or plate boundaries, rocks deform, crack and fail, which modifies the pore space by either compaction (for instance, collapse of open pores due to grain crushing) or dilation (generation and propagation of new open cracks). These changes in pore space generate local fluid pressure variations and also have a great impact on the ability of fluids to move through rocks and faults. Interestingly, the fluid pressure and fluid flow patterns also have an impact on the deformation of rocks, therefore forming complex feedbacks that determine the overall strength of faults and the long-term tectonics of the Earth's crust. Our understanding of crustal fault mechanics therefore relies crucially on our knowledge of the spatio-temporal distribution of pore pressure in the crust.Our quantitative understanding of the feedback processes between deformation, fluid pressure and fluid flow in rocks is currently limited by our ability to measure in-situ rock properties, which are required for large scale model predictions. One of the key problem limiting our understanding is that rock deformation and fluid pressure and flow are coupled through large but very local porosity changes occurring prior to, during and after brittle failure.The goal of the proposed research is, therefore, to unlock this knowledge gap by conducting innovative laboratory experiments that make use of an array of a newly developed type of fluid pressure transducer capable of monitoring local and rapid changes in pressure throughout deformation. By positioning a 3D array of such transducers around laboratory rock samples, we will monitor (1) spatio-temporal localisation of dila- tancy/compaction during quasi-static and dynamic rupture, and (2) the development of heterogeneity and anisotropy in fluid transport properties. Ultimately, our experimental results will provide the key to the time-evolution of fault zone physical properties that are currently unavailable, but which are essential to fully evaluate the role of pore fluid pressure during deformation and faulting in the crust.