Yuntao Ji, André Niemeijer, Dawin Baden, Futoshi Yamashita, Shiqing Xu, Luuk Hunfeld, Ronald P. J. Pijnenburg, Eiichi Fukuyama, Christopher Spiers

A central question in modeling induced and natural earthquake nucleation is whether fault frictional properties measured in the laboratory are applicable to nature. A laboratory fault is generally just a few centimeters in length-width scale, while natural faults can be hundreds of meters to kilometers in extent. It is unknown whether laboratory fault friction data are applicable even to mesh dimensions (~1m) of earthquake simulators used in seismic hazard analysis. We report the first m-scale friction experiments on simulated fault wear material (gouge), performed at sliding rates relevant for earthquake nucleation. We show that fault friction and its dependence on slip rate, distance and gouge state are indistinguishable from those measured at cm-scale, despite heterogeneities in stress and slip velocity detected along the m-scale fault plane. We attribute this scale independence to slip being accommodated on microscale shear bands that evolve similarly at all scales, independently of heterogeneities in gouge density and boundary conditions. Our results imply that parameters derived from cm-scale friction experiments are directly applicable to modeling induced and natural earthquake nucleation on planar faults and provide key baseline data for future investigations into the effects of natural heterogeneities in gouge composition and fault topography on frictional scaling.