Intermittency of earthquake cycles in a model of a three-degree-of-freedom spring-block system

We herein report the results of some numerical simulations of complex earthquake cycles using a threedegree-of-freedom spring-block model with a rateand statedependent friction law. The model consists of three blocks on a conveyor belt that is moving at a steady rate. Observed complex slip behaviour in the simulations is classified into five slip patterns, and for each of these the parameter dependence of the slip patterns is demonstrated by means of phase diagrams. Aperiodic slip patterns occur for wider ranges of the parameter space in the three-block system than in the two-block system. Chaotic slip behaviour known here as “intermittency” is found in the three-block system, in which two different slip patterns occur alternately with variable durations. By calculating Lyapunov exponents, we quantify the dependence of slip evolution on the initial conditions for each slip pattern. For cases where intermittent slip patterns occur, the time evolution of the Lyapunov exponent is correlated with changes in slip behaviour.