Applications of Rate- and State-Dependent Friction to Models of Fault-Slip and Earthquake Occurrence

Abstract

The rate- and state–dependent constitutive formulation describes characteristic dependencies of fault friction on slip, slip rate, slip history, and normal stress history observed in laboratory studies, and it provides a unified framework for predictive modeling of diverse sliding phenomena observed for faults in nature and in the laboratory. Simulations of fault slip that employ rate–state friction provide representation of the conditions required for, and the characteristics of, stable and unstable fault slip, including the onset of slip instabilities, earthquake afterslip, and aseismic creep events. Laboratory observations and theoretical models indicate that earthquake nucleation is highly time–dependent and consists of a long interval of self–driven accelerating slip. The dimensions of the nucleation zone follow scaling relations for the minimum critical length for unstable slip, and also define a minimum fault length for earthquake slip. A formulation for earthquake rates, which is derived using rate- and state–dependent friction, forms the basis of an integrated approach to quantitatively model the effects of stress changes on earthquake rates. Foreshocks, aftershocks, and triggering phenomena are modeled. The earthquake rate formulation has been used in an inverse mode to infer stress changes from changes of seismicity rates.