Concurrently, he posits, a crack-like solution propogates homogeneously, interacting with discontinuities at fault region edges or with gouge of differing viscosity. Finite tectonic stress occurs along the faults. A viscous crack responds to a slow stable slip in the quasi-static stress field, inducing nouniformly distributed deformation which diffuses or propogates along a fault. Meanwhile, a brittle fracture occurs. Both release stress along the fault in situations with sufficient time constants which depend on the gouge viscosity, fault thickness and other parameters.
Diffusion apparently reduces stress concentration, encouraging creep rather than seismic rupture.
Fault heterogeniety may contribute to perturbations that interrupt viscous crack propogation. Blockage causes stress accumulation until unstable fracture releases the strain. Central California creeping faults seem to show that acccumulation occurs nonuniformly, since creep offset propogates elliptically. Once stress reaches the yield point, gauge fails and continues to flow, thus decreasing elastic strain and stress in the surrounding media. They recognize that the model produces a non-unique solution for observed creep events.