Dependency of nucleation behavior on fault surface characteristics related to roughness and asperity populations: An experimental study on Carrara Marble

Foreshocks in nature are localized frictional instabilities that are believed to be related to variations in frictional strength along the principal rupture plane. Along this plane, the contact nature induced by the coming together of rough-rough surfaces is believed to dictate the stress field heterogeneity and, in turn, complex rupture behaviors. In this study, we examine contact conditions formed on dry and bare surfaces where the contact is established through asperities, which are the geometric interactions between surface heights that lead to normal stress concentrations. We aim to further characterize the stress heterogeneity caused by fault surface topology and link this to preparatory processes of seismicity associated with asperities populations. In the laboratory environment, where the stress conditions are controlled, heterogeneity related to the strength of the asperities can be explicitly mapped. We used the Fuji Prescale pressure sensitive film to map the normal stress variations caused by the asperity population on a saw-cut frictional interface imposed on a cylindrical sample. Using the apriori understanding of the contact nature, we proceeded to conduct triaxial loading experiments on the precharacterized saw-cut Carrara Marble samples in dry and unlubricated conditions. Using acoustic emission monitoring and strain field monitoring via the deployment of fiber optics, allowed us to characterize the aseismic deformation and precursory seismic sequences with high resolution. Detailed stress mapping of the fault surface prior to and after each experiment provided unique insight into the evolution of the asperity population connected with seismicity in the laboratory environment