Seismic faults are rough, and their geometrical complexity is an important research topic. In this work, we present a numerical model dedicated to the simulation of friction and wear in an idealized fault asperity, taking inspiration from an experimental device used in a companion paper. The model can simulate the progressive damaging of the fault rock close to the contact, the release of fault gouge in the interface, and its circulation in the asperity and ejection from it. This allows to explore the complex interplay between a geometrical asperity and a gouge layer, in the presence of wear. Numerical results show that the asperity spontaneously evolves towards a tribological steady state in terms of friction, wear rate, roughness, and gouge thickness, in qualitative (and sometimes quantitative) agreement with experiments. We show that the existence of a geometrical asperity does not preclude the presence of a persistent gouge layer, which properties control the tribological response of the interface, and we emphasize the importance of understanding the mechanical, geometrical and rheological factors controlling its thickness.

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. 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 behaviour of the down-scaled lab fault. The results for low sliding velocity (0,01 m.s-1) tests shows a complex behaviour. 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.