Collaborative Research: Mechanics of Earthquake Fault Zones: Particle Dynamics Simulations and Laboratory Experiments

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Laboratory studies have contributed significantly to our understanding of earthquake nucleation, dynamic rupture, and shear deformation, however, results of these experiments are often difficult to scale up to natural fault systems. Particle-based numerical models, which have successfully reproduced a wide-range of observed laboratory and natural phenomena, can help. This collaborative research project is designed to (a) improve and refine existing particle-based numerical techniques to better replicate laboratory experimental results, in particular, first and second order variations in frictional strength and sliding stability, and (2) bridge the gap between these improved models and natural faults, allowing investigation of the structural evolution of complex tectonic faultsThis research involves parallel laboratory and numerical experiments, conducted under a wide range of identical initial and boundary conditions. The experimental and numerical results are being compared, guiding updates of the numerical interparticle contact laws to better reproduce realistic physico-chemical surface interactions. The primary focus is on accurately constraining the base ("Byerlee's Law") coefficient of sliding friction in the two sets of experiments, as well as its variation with shear, dilation, and compaction. Focus will also include the 2nd-order variations in friction with contact time and slip velocity, i.e., rate- and state-dependent friction. The numerical models further help to isolate the deformation mechanisms acting within the fault zones under different boundary conditions, including shear localization, grain-boundary sliding, particle rolling, translation, and fracture. Results of the proposed work will have significant impact on understanding fault mechanics and earthquake physics including fault interaction, earthquake triggering, and seismic hazard assessment.