Detailed experimental studies of the characteristic friction distance Dc are needed to understand frictional instability and the mechanisms of failure during earthquakes. For bare rock surface Dc is thought to represent the displacement necessary to change completely the population of surface contacts; an interpretation supported by data showing that Dc scales with surface roughness. In fault gouge it does not necessarily follow that contact size, and thus Dc, will scale with surface roughness, since particle- surface contacts will be controlled by particle size as well as surface roughness. The motivation for the experiments is the observation that surface roughness does affect Dc of gouge, even after shear has localized. Since this means that the surface roughness effect on Dc cannot be explained solely as a consequence of contact size it raises the question of what controls Dc for sliding within gouge. This project involves a systematic study of the effect of surface roughness on Dc of gouge. The work will have two specific objectives: 1) to expand the database for the surface roughness effect on Dc to roughnesses 10-100 times that of existing data, and 2) to investigate the micromechanics of Dc in gouge via detailed mechanical and microstructural measurements.
