Slip-behavior transitions of a heterogeneous linear fault

Geological faults have frictional heterogeneity. Here we investigate the slip behavior of such heterogeneous faults in the simplest situation, simulating antiplane shear slip along an infinite linear fault in a 2-D elastic model space, subjected to constant loading by external stresses characterized by stiffness and plate-motion velocity. The fault is discretized into many subfaults, each of which has either a velocity-weakening (VW) or velocity-strengthening (VS) friction law. We vary the proportion of the fault that is VW, revealing several different regimes of slip behavior. The first regime boundary, where stick-slip behavior is initiated, is located at the proportion of VW zones such that each VW zone reaches its nucleation size. The other boundary is located where the spatially averaged a-b value of the rate and state friction law is close to zero. Below this density, the VW zone slips seismically, whereas the VS zone shows afterslip. In contrast, above this density, the entire fault slips simultaneously at the seismic slip velocity. We observe transitional behavior at the second boundary, where relatively slower deformation dominates. We also explore the slip behavior of faults using Cantor-set distributions of frictional parameters. We propose that frictional heterogeneity on the fault may explain not only the diversity of seismic phenomena but also the observed scaling of frictional parameters, such as slip-weakening distance or the fracture energy of ordinary earthquakes.