Collaborative Research: Laboratory and Theoretical Investigations of the Micro-Mechanical Origins of Rate and State Friction on Tectonic Faults

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In the earthquake-cycle, tectonic faults slowly accumulate stress, due to plate tectonic motion of Earth?s surface, and then fail catastrophically in earthquakes. One of the keys to simulating the earthquake cycle are friction laws that can be applied to both the fast, dynamic motion of earthquakes, as fault rocks rub and slide past one another in frictional contact, and the slow processes of stress accumulation between earthquakes that can take hundreds of years. In this collaborative work between Princeton and Penn State Universities, unusually well-controlled measurements of frictional sliding will be conducted while collecting simultaneous ultrasonic data on the sliding interfaces and sheared layers of fault gouge. The proposed work has important societal implications for seismic hazard assessment, earthquake forecasting, and an improved, fundamental understanding of earthquake nucleation.Rate-and-state friction laws represent the current state-of-the-art in the laboratory and for numerical simulations of earthquake physics, including nucleation, dynamic rupture and the complete seismic cycle. However, our understanding of friction memory effects and slip velocity dependence remains primarily empirical, which limits our ability to apply laboratory measurements to earthquake faults and/or to address the problems associated with predicting the behavior of tectonic faults from laboratory measurements. To address these shortcomings, recent advances in ultrasonic monitoring of sliding rock surfaces and sheared granular fault gouge will provide fundamental insights into the physics and micro-mechanical origins of frictional behavior of tectonic faults.