Period doubling as a result of slip complexities in sliding surfaces with strength heterogeneity

Period doubling bifurcation of stress drop is one of the non-linear dynamic phenomena in the transition from stable sliding to stick-slip of rock fric tion, and the onset of period doubling has been suggested to be related wit h stiffness and constitutive parameters as well as load point velocity. How ever, we find in the experiment that period doubling bifurcation of stick-s lip can occur due to macroscopic heterogeneity of the sliding surface under conditions favorable for the occurrence of stick-slip. The strain measurem ent shows that the period doubling bifurcation of stress drop results from the alternate occurrence of strain release along whole fault and that along parts of fault, i.e. strong patches of fault. We conduct numerical analysi s using a two-block model based on the rate and state friction law, and it confirms the experimental result. The numerical results show the interactio n between the two blocks in detail during single and double stress drops. T he strong block is active and moves spontaneously in the early stage of ine rtial motion, and the weak block is either to be loaded aseismically or tri ggered to produce stress drops by the velocity pulse in the strong block. N umerical results also show that the stress drops in both strong and weak se gments are comparable despite the big contrast in strength and rate depende nce. (C) 2001 Elsevier Science B.V. All rights reserved.