부산대학교 도서관

Two key parameters control the localization of deformation and seismicity along and surrounding crustal faults: the strength and roughness of the pre-existing fault surface. Using 3-D discrete element method simulations, we investigate how the anisotropy and amplitude of roughness control the mechanical behaviour of healed faults within granite blocks during quasi-static triaxial compression. We focus on models in which the uniaxial compressive strength of the healed faults is about 25 per cent of that strength of the surrounding host rock. These models provide insights into the evolution of fracture network localization, fault roughness, gouge production, fault slip and stress concentrations along initially healed faults of varying roughness. In contrast to expectations, the uniaxial compressive strengths of models that host faults with root-mean-squared roughness amplitudes of 0.2–1.4 mm do not vary more than the change produced by variations in particle packing. To assess if this lack of influence arises from the evolving roughness of the faults, we track the roughness amplitudes parallel and perpendicular to the downdip direction throughout fault failure and slip. The de facto roughness does not provide an explanation for the lack of influence of roughness on compressive strength because the roughness of the faults does not evolve to similar values with slip. Rather, smoother faults remain smoother than rougher faults throughout the simulation. However, the rougher faults produce larger volumes of gouge than the smoother faults. The gouge lubricates the fault and thereby reduces the influence of roughness on compressive strength. These observations suggest that fault topography and the asperities that build this topography do not exert a significant impact on deformation. To quantify the influence of asperities on slip, we calculate correlation coefficients between the fault surface topography and components of the slip vectors. The observed negative correlation coefficients between the fault topography and fault-plane parallel slip quantify the degree to which asperities slow slip in the downdip direction. The observed positive correlation coefficients between the topography and fault-plane perpendicular movement quantify the degree to which asperities promote opening. Thus, this analysis shows how asperities control slip by acting as speed bumps that hinder fault-plane parallel slip and promote fault-plane normal opening as the healed faults slide. The asperities do not significantly control fault movement during the unlocking and failure of the healed faults, but only following the peak axial stress as the faults slide and damage zones develop. These models thus provide unparalleled access to the dynamics of reactivated healed faults. [ABSTRACT FROM AUTHOR]