Oral Presentation

While our understanding of earthquake processes has been guided by insights provided by laboratory experiments, the application of lab data to natural conditions requires daunting extrapolation in spatial scale and, for interseismic deformation, time scale. At a broad level, a combination of in situ stress measurements and geologic observations support canonical friction coefficients for (some) fault zones. Conversely, independent observations of fault orientation and geophysical/seismic observations indicate that stresses on seismogenic faults are often much lower than predicted by simple application of laboratory data. In this presentation, I will outline several features of fault behavior for which scaling in scale and time are important. In the context of rate-and-state friction, the velocity dependence of friction arises from asperity scale plasticity (which at its core reflects the kinetic response of viscous creep mechanisms). How well can we account for these kinetic effects by trading off time and temperature in the laboratory? How do long-term, very slow displacement rate experiments inform our understanding of these processes? What roles do changes in cohesion play in these processes? In this context, a combination of microstructural observations and thermochronolgical data on exhumed fault zones (e.g., SCEC-funded work with Alexis Ault and Alex Dimonte) can be analyzed to constrain relationships among temperature, slip rate, fault rock composition and the modes of fault slip at time scales well-beyond the duration of a lab test. Similarly, by their nature, laboratory experiments are conducted on geometrically simple “fault zones”. With several collaborators (Victor Tsai, Daniel Trugman, Jaeseok Lee, Avi Chatterjee, Shanna Chu) we have been investigating correlations among fault structure, earthquake stress drops, fault creep rate, and patterns of radiated energy. These analyses provide new insight into how fault behavior is impacted by the “complexity” of fault zone structures.