Université de Strasbourg

Shear in faults

Modelling mechanical evolution of slip surfaces during shear in faults

USIAS Fellow : Amir Sagy

Since natural faults are rough at all scales, understanding how the non-planarity of the fault affects rupture behavior has become essential for many aspects of seismic hazards and earthquake modeling. Yet, there is a dearth in physical theory for describing or quantifying the evolution of fault surface geometry during slip. The goal of this project is therefore to analyze the geometrical evolution of slip surface and to develop a mechanical model and framework for further research. Our analysis is based on two separated sets of data that we collected recently. First, fault surface geometry has been measured using ground based LiDAR in several field outcrops. Second, we developed unique laboratory method to measure the geometrical evolution of slip surfaces as function of slip distance and normal stress. Our measurements already established that fault surfaces are smoothed by successive slip events. It is however not trivial to connect the experimental results to natural faulting, primarily because the scales of geometrical irregularities and slip magnitudes are diverse in the two systems. In the absence of mechanical model, it is also unknown how wear affects fault geometry on different scales and to what degree rock is ground down under the high normal stresses typical to seismogenic zones.  Our aim is therefore to develop a simple model that quantifies the geometric evolution of fault surface due to the wear of its asperities.

Investissements d'Avenir