Single-Asperity Friction and Wear in Seismic Faults: 1. Experiments on Marble

Abstract

Common representations of seismic faults often fall into two categories. Either the model focuses on clean rough surfaces in sliding contact, or the model focuses on the gouge production and shearing between two smooth surfaces. In this work, we wish to reconcile these two main models by using tribological tools and concepts, in order to pave the way for a more accurate model of geometrically complex faults. A pin-on-disc experimental device is employed to investigate the response of a single asperity to shear sliding, in presence of granular gouge. Near co-seismic conditions are applied on Carrara marble samples (contact stress, contact area, sliding velocity) and real time acquisition sensors as well as post-mortem analyses on the contact surfaces provide qualitative and quantitative information on the frictional behavior of the downscaled lab fault. The results for moderate sliding velocity (0.01 m s⁻¹) tests show a complex behavior. Three regimes are underlined, which highlights the interplay between granular gouge and asperities. The last regime is seen as a steady state with rough contact surfaces and the presence of a granular gouge layer. This observation leads to the conclusion that in a model for geometrically complex fault, granular gouge and asperities are not self-excluding and should be considered together. This work is complemented by a numerical model presented in a companion paper.