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A Unified Fracture Mechanics Model for Fault Slip Throughout the Seismic Cycle: Interseismic Decoupling, Precursory Transients and Earthquake Nucleation

Description: 

Laboratory experiments suggest that fault slip evolves in predictable ways prior to frictional instabilities. However, precursory processes on tectonic faults remain enigmatic: how does slip evolve throughout the seismic cycle, and under what conditions are earthquakes preceded by slow transients? Here I introduce a minimal fracture mechanics model to describe fault slip throughout the seismic cycle on heterogeneous faults. Slipping patches are represented as 2-D cracks with propagation controlled by energy balance at the crack tip. In contrast to previous models, this approach explicitly accounts for interseismic loading, and it seamlessly describes the transition from quasi-static interseismic slip to nucleation, thus providing new insights into precursory slip.

I consider two types of heterogeneity: 1. frictional heterogeneity in lithology or normal stress, 2. stress heterogeneity due to non-uniform loading. The early interseismic cycle is characterized by steady migration of creep fronts into regions of decreasing stress or increasing strength. For uniform loading and a low degree of heterogeneity, this is followed by an abrupt transition to earthquake nucleation, without precursors. In contrast, a higher degree of heterogeneity gives rise to an intermediate stage characterized by slow transients, akin to “failed nucleations”. I discuss several applications, including fault slip induced by fluid injection; slow slip at the boundary between locked and creeping faults; slow slip driven by the presence of subducted seamounts. In each case, the fracture mechanics criterion defines stress conditions favorable to slow transients, which are confirmed by numerical simulations of rate-state faults. These results indicate that fault heterogeneity can produce diagnostic and predictable changes in interseismic slip behavior throughout the seismic cycle, including precursory slow transients. The emergence of these slip patterns in a minimal fracture mechanics model suggest that they may be rather universal, driven by the stabilizing effect of crack propagation into regions of decreasing stress or increasing strength.

Session: Predictability of Seismic and Aseismic Slip: From Basic Science to Operational Forecasts - I

Type: Oral

Date: 4/16/2025

Presentation Time: 04:45 PM (local time)

Presenting Author: Camilla

Student Presenter: No

Invited Presentation: Yes

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