An experimental study of the effect of off-fault damage on the velocity of a slip pulse

[1] The effect of off-fault damage on the speed of ruptures propagating on faults in photoelastic Homalite plates was measured using high-speed digital photography. The offfault damage was composed of a network of fractures introduced by thermally shocking the Homalite in liquid nitrogen. The mode II rupture speed measured in damaged Homalite was significantly lower than the limiting Rayleigh speed of vr = 0.92 vs, even after the shear wave speed vs was reduced to a value appropriate for the fracture-damaged Homalite. The additional slowing is most likely caused by frictional sliding on preexisting cracks, especially since we did not observe the generation of new fractures. The spatial extent of the interaction between the rupture and the off-fault damage was measured using samples in which the damage was limited to a band of width 2w centered on the fault and also using damaged samples containing a band of undamaged Homalite centered on the fault. By measuring the rupture velocity as a function of w, the interaction between the rupture and off-fault damage was observed to be limited to a distance of about 1 cm from the fault plane. This agrees with the spatial extent of Coulomb failure near the tip of a dynamic slip pulse predicted by the analytic model developed by Rice et al. (2005).