Faulting and healing of the crust throughout the seismic cycle: From microscale physico-chemical processes to a global rheology

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In the Earth's upper crust, geological deformation is primarily accommodated by fracturingand faulting. Fault motion can be catastrophic and generate earthquakes, but these are rather rare events in time: most faults in the crust are either very slowly moving (creeping) or completely locked between earthquakes. During this so-called interseismic period, fractures heal (i.e., they regain strength) and seal (i.e., they close paths for fluid flow) due to chemical lithification processes. The competition of healing and sealing processes with fracture growth conditions the location and timing of future earthquakes along faults. Hence, understanding how rocks heal and fracture, and the feedbacks between these processes, is an essential step towards a better knowledge of earthquake generation and the associatedhazards. Despite the considerable attention this problem has received since the late 1970's,mostly through the development of phenomenological frictional constitutive laws, very little isknown in terms of actual microscale mechanisms, from which the observed empirical macroscopic laws couldarise. In particular, a unifying micromechanical framework encompassing fracture gowth, healing andsealing remains to be determined. Therefore, I propose to tackle this problem from a different pointof view, by (1) identifying and quantifying experimentally the physico-chemical processes controllingultra-slow deformation and fracture healing, and (2) theoretically input those processes into a rigorousmicromechanical framework that can be used to extrapolate from the laboratory to field scale.