PERIOD DOUBLING AS A RESULT OF SLIP COMPLEXITIES IN SLIDING SURFACES WITH STRENGTH HETEROGENEITY

Abstract

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 friction, and the onset of period doubling has been suggested to be related with stiffness and constitutive parameters as well as load point velocity. However, we find in the experiment that period doubling bifurcation of stick-slip can occur due to macroscopic heterogeneity of the sliding surface under conditions favorable for the occurrence of stick-slip. The strain measurement 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 analysis using a two-block model based on the rate and state friction law, and it confirms the experimental result. The numerical results show the interaction between the two blocks in detail during single and double stress drops. The strong block is active and moves spontaneously in the early stage of inertial motion, and the weak block is either to be loaded aseismically or triggered to produce stress drops by the velocity pulse in the strong block. Numerical results also show that the stress drops in both strong and weak segments are comparable despite the big contrast in strength and rate dependence.