On the nucleation of creep and the interaction between creep and seismic slip on rate- and state-dependent faults

Previous studies of rapture nucleation were restricted to conditions well within the unstable regime. In this study, we show that positive stress changes applied on intrinsically stable interfaces can trigger quasi-static slip episodes. Similar to the onset of ruptures on unstable fractures, the creep on intrinsically stable fractures too are preceded by intervals during which the slip is highly localized. The size of the nucleation patch depends not only on the constitutive parameters, but also on the stressing history. We examine the effect of a stress step on the slip history of a seismic fault interacting with a creeping segment, and show that stress transfer due to creep may strongly affect the timing of an impending seismic slip. Finally, we investigate the effect of a stress step on the slip history of an isolated unstable strip surrounded by creep, and show that a positive stress step triggers aftershocks, whose rate decays as 1/time during most of the sequence, but much faster than 1/time shortly after the stress step.