The investigators propose a systematic study to understand the fundamental processes responsible for the various effects recognized in rock friction. They will conduct experiments aimed at understanding what processes are responsible for the time dependence of interaction between single frictional contacts, multiple contacts, and contacts in gouge, especially on slip surfaces within gouge. The purpose is to understand the frictional behavior observers might expect to find on faults during most parts of the earthquake cycle. The problem is that the well-known empirical rate and state friction description of friction, as determined in the laboratory, cannot presently be extended to faults in the Earth with any confidence, because we do not understand the fundamental processes underlying the behavior. To understand earthquake nucleation it is a fundamental requirement to understand the time dependence that allows faults to strengthen between dynamic events and causes them to weaken as slip accelerates. The investigators will conduct a series of microindentation and friction experiments designed to differentiate between the most likely classes of explanations by variation of fluid chemistry and temperature and through an intensive microstructural study.
