Following Individual Ruptures: A New approach for Measuring Dynamic Friction in the Lab

At the core of every earthquake lies a dynamic rupture event propagating at high speeds along a fault (frictional interface) in the Earth's crust. Friction plays a central role in determining how such ruptures propagate, by influencing their speeds and modes, and how they release waves that cause destructive shaking threatening our infrastructure and endangering our lives. The detailed nature of the underlying dynamic friction is one of the biggest uncertainties in earthquake mechanics, a fact which limits our ability to model earthquakes accurately and to mitigate their effect to the built environment. To better understand the dynamic frictional laws at play, we have proposed and developed a unique experimental methodology combining high-speed full-field imaging with digital, ultra-high-speed photography. Together with a laboratory-scale replication of seismic events, this technique allows us to follow individual ruptures at high resolution and in real time in vitro - i.e., on the laboratory scale under conditions mimicking real earthquakes. With this method, we can measure the evolving on-fault friction in real time as well as the associated ground shaking, in both strike-slip and thrust configurations and to unravel the history dependent nature of friction on slip, slip rate as well as fast variations in normal stress. Our findings provide guidance to theoretical earthquake source mechanics models by furnishing the necessary on-fault physics needed for the numerical simulation of the rupture process.