The spectrum of fault slip in elastoplastic fault zones

Abstract

Natural faults are typically surrounded by damage zones that exhibit inelastic material response. This study investigates the role of fault zone strength in modulating the spectrum of fault slip across different spatio-temporal scales. We carry out long-term simulations of seismic and aseismic slip for an elastoplastic spring slider model with rate-and-state friction as well as a continuum model of a 2D anti-plane rate-and-state fault embedded in an elastoplastic bulk. Results of the elastoplastic spring slider model show the emergence of a new stability boundary, depending on the bulk yield strength relative to fault frictional strength, that limits the rupture size regardless of the fault length. Continuum simulations generate a spectrum of slip analogous to the spring slider model including localized or migrating events of slow and fast slip. A fault may remain locked for yield strength sufficiently low and close to fault reference strength even if it is intrinsically rate weakening and larger than the nucleation length scale predicted by the elastic analysis. These findings shed new light on the nature of fault frictional stability and suggest the critical role of the fault zone rheological properties in modulating the spectrum of fault slip.