Low displacement fracture damage plays an important role in influencing the behavior and mechanical evolution of faults. Fracture damage zones influence slip behavior through changing near-field stress orientations, altering fluid pathways and modifying fault structure. Here we use small displacement triaxial experiments to explore the development of fault zone damage, frictional lock-up, and the generation of new faults using samples with preground faults, oriented in 5 degrees increments between 25 degrees and 65 degrees relative to the shortening direction. With increasing reactivation angle, faults support higher peak normal stresses (104-845MPa) and behavior transitions from stable sliding to stick slip. Frictional melting occurs on surfaces where stick slip is initiated, forming micron-thick layers that locally weld asperity contacts. The extent of melt welding is correlated with normal stress and melt-welded zones increase fault cohesion. Distribution of fracture damage adjacent to the fault is spatially correlated with melt-welded zones and the corresponding concentrations of stress and elastic strain. In a process referred to as adhesive wear, fractures bypassing welded zones transfer melt-adhered material from one side of the fault to the other, forming new geometric asperities. On faults with high reactivation angles (55 degrees-60 degrees) the increase in cohesive strength resulting from melt-welded contacts drives fault lock-up after an initial slip event; subsequent slip localizes on new, favorably oriented faults. Given their size, melt-welded zones are likely to be short-lived in nature but may play a significant and previously unrecognized role in the development of fault-related damage.
