Micromechanics of asperity rupture during laboratory stick slip experiments

Acoustic emissions and tremor-like signals are widely recorded in laboratory experiments. We are able to isolate the physical origins of these signals using high resolution nanoseismic analysis. The use of a picometer-sensitive, wide-band sensor array permits us to determine force-time functions and focal mechanisms for discrete events found amid the noise of friction, similar to how low frequency earthquakes are found buried within tremor. We interpret these localized events to be the rupture of mm-sized contacts, known as asperities. We performed stick-slip experiments on plastic/plastic and rock/rock interfaces and found a systematic difference between the nano earthquakes: the rock interface produces very rapid (< 1 mu s) implosive forces indicative of brittle failure and fault gouge formation, while rupture on the plastic interface releases only shear force and produces a nano quake more similar to earthquakes commonly recorded in the field. The difference between the mechanisms is attributed to the vast differences in the hardness and melting temperatures of the two materials, which affect the distribution of asperities as well as their failure behavior. With proper scaling, the strong link between material properties and laboratory earthquakes will aid in our understanding of fault mechanics and the generation of earthquakes and tectonic tremor. Citation: McLaskey, G. C., and S. D. Glaser (2011), Micromechanics of asperity rupture during laboratory stick slip experiments, Geophys. Res. Lett., 38, L12302, doi: 10.1029/2011GL047507.