Collaborative Research: Investigating the interplay between creeping and seismogenic fault sections using large-scale laboratory experiments and high-resolution numerical models

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Frictional and material properties vary along tectonic faults and directly affect the nucleation, propagation and arrest of earthquakes. This heterogeneous character of natural faults is what makes earthquakes complex and difficult to predict. Some fault sections are mostly locked but recurrently host earthquakes. Other sections are creeping and generally stable. However, under poorly understood circumstances, earthquakes that nucleated in an unstable section can propagate far into stable fault sections and result in particularly large and destructive events. This project investigates the causes that lead to activation of the creeping fault sections by combining large-scale laboratory earthquake experiments with physics-based numerical simulations. The modeled fault consists of stable and unstable parts which realistically reproduce the mechanics of earthquakes at heterogeneous faults. A better understanding of the interaction between stable and unstable fault sections will help us evaluate the potential for extremely large earthquakes that will likely enhance existing seismic hazard assessment tools. This project is a benefit to society because it will help us to better understand earthquakes and develop tools to assess these hazards, and it will add to STEM education of students while supporting new researchers in earthquake studies.This research is a collaborative effort to investigate the mechanics of earthquake rupture arrest with focus on heterogeneous fault properties. It combines multiscale laboratory experiments and numerical modeling. The experiments provide physical constraints for the numerical models, while the modeling improves understanding, generalizing, and scaling up the experimental results. Large-scale laboratory earthquake experiments are conducted on a biaxial machine that generates repeatable sequences of dynamic rupture events contained within a 3-m long granite sample. The fault surfaces are coated with gouge to generate patches of velocity-weakening and velocity-strengthening materials. To explore scaling effects, additional experiments are conducted on a 0.76 m tabletop biaxial machine using plastic samples as forcing blocks. Smaller-scale double-direct shear experiments will benchmark the frictional constitutive parameters of the gouge materials, an essential step for the interpretation of the larger-scale laboratory earthquake observations and the development of realistic, high-resolution numerical models of dynamic rupture and arrest. The simulations include sequences of slip events that quantitatively reproduce the relevant scales of the experiments including the actual size of the apparatus and the rupture process zone.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.