Mechanics of Earthquakes, Creep and Slow Slip - A Laboratory Perspective
The discovery of unusual deformation phenomena like tectonic tremor, episodic tremor and slip, and slow earthquakes has renewed interest in friction and rheology of active faults. Indirect evidence of elevated pore pressure suggests that fluids likely play an important role. Many of the more unusual deformation modes appear to occur in the transition from brittle to ductile deformation and therefore can involve complex interactions of chemical, mechanical and poroelastic processes. We look at laboratory deformation tests of rate- and state-friction parameters, especially near critical loading stiffness. In this region, complex deformation patterns appear that suggest nonlinear fault properties. These include periodic stress oscillation (i.e., slow slip and creep episodes), period doubling, and spontaneous jumps between attractors in limit cycles. Many of these features can be understood in terms of rate- and state-friction, but some cannot.