EAR-PF The scale-dependent interplay between fault material strength, roughness and friction

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Dr. Valère Lambert has been awarded an NSF EAR Postdoctoral Fellowship to investigate the ways that rock strength, the shape of a fault’s surface, and friction can affect the behavior of faults and thus hazards associated with earthquakes. The majority of what is known about the mechanics of faults comes from small-scale (1 meter) experiments but natural fault systems are much larger (tens to thousands of meters). Because laboratory experiments and numerical studies indicate that rock strength and friction measurements vary with scale, application of laboratory experiment results to natural systems requires careful consideration of how to adjust for differences between natural and laboratory scales. This study aims to establish a framework for scaling up by clarifying relationships among rock strength, the shape and roughness of the fault surface, and friction at a variety of scales. Determining a framework for appropriately-scaled descriptions of friction and rock strength has important implications for earthquake science and engineering. The project will also support research opportunities for undergraduate students as University of California Santa Cruz, as well as development of educational earthquake simulations and an outreach video series oriented towards the general public addressing topics in earthquake physics.Obtaining a better understanding of the relationship between fault material strength and the deformation of fault asperities at varying scales will contribute to our general understanding of fault topography evolution and frictional behavior. This project will assess the feasibility of using measurements of fault roughness as the basis for bridging laboratory and natural scales and aims to develop computational homogenization tools for determining macroscale material and structural features from microscale fault properties. The project will directly measure the scale-dependent material properties of natural fault samples in the laboratory and explore how the aggregate behavior of microstructural features, such as material heterogeneity and layering, maps into the yielding of surface asperities at varying scales. The project will then explore what role scale-dependent material strength plays in the evolution of fault roughness and the apparent frictional behavior under shear motion. This work will examine if there is an inherent link between scale-dependent material properties and structure, both in the topography of the interface as well as material layering. If such a relationship exists, this may form the basis to a scheme for inferring spatial trends in rock strength and extrapolating frictional behavior to field scales using extant measurements of fault roughness. Such an approach could have broad applications in materials science, including implications of material layering on frictional behavior.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.