Nucleation and arrest of dynamic slip on a pressurized fault

Abstract

[1] Elevated pore pressure can lead to reactivation of slip on pre-existing fractures and faults when the static Coulomb failure is reached locally. As the pressurized region spreads diffusively, slip can accumulate quasi-statically (paced by the pore fluid diffusion) or dynamically. In this work, we consider a prestressed fault with a locally peaked, diffusively spreading pore pressure field to study (1) conditions leading to the escalation of slip and nucleation of dynamic rupture and (2) rupture run-out distance before it is arrested. Nucleation appears in this model when the fault friction decreases from its peak value with slip, while arrest of dynamic propagation is imminent on aseismic faults (i.e., such that prestress t b is less than the residual fault strength t r at ambient conditions). When fluid overpressure is a small-to-moderate fraction of the ambient value of normal effective stress (and prestress is large enough for fault slip to be activated by overpressure), dynamic rupture always nucleates, and the nucleation length increases with decreasing prestress practically independently of the overpressure value. Transition from the ultimately unstable (t b > t r ) to the ultimately stable (t b < t r ) fault loading is marked by a strong increase of the nucleation length (∝1/(t b À t r ) 2 ) as t b approaches t r from above. For aseismic faults (t b < t r ), no dynamic rupture is nucleated at large fluid overpressures for all but the smallest values of prestress. The largest run-out distances of dynamic slip on aseismic faults correspond to overpressure/prestress just sufficient for slip activation. In such cases, the dynamically accumulated slip can lead to enhanced, dynamic fault weakening, resulting in a sustained dynamic rupture and generating a large earthquake. This is consistent with field observations when the largest injection-induced seismicity occurred after fluid injection ended.

On the initiation of sustained slip-weakening ruptures by localized stresses

“…Beyond its significance for computational earthquake dynamics, the fundamental understanding of the conditions that enable self-sustained (also called runaway) ruptures near an overstressed asperity can contribute to the quantitative assessment of failure and hazard in a range of contexts that involve loading by a concentrated stress. These include the nucleation of earthquakes and foreshocks driven by stress concentration near the boundaries between creeping and locked fault areas, for example at the base of the seismogenic zone; the initiation of frictional sliding near point loads in laboratory experiments (Rubinstein et al 2007;Kammer et al 2014); induced seismicity near concentrated loads generated by fluid injection (Garagash & Germanovich 2012), and the initiation of landslides by locally elevated pore pressures (Viesca & Rice 2012). The overstressed asperity initiation is admittedly a crude representation of these situations, but it encapsulates some of their key physical ingredients and hence is a basic model that can provide insight into more realistic situations, as illustrated by the work of Ampuero et al (2006) and Ripperger et al (2007).…”

“…Campillo & Ionescu 1997;Ampuero et al 2002;Uenishi & Rice 2003) established critical length scales for the onset of self-accelerating slip, but did not consider whether the rupture became indefinitely selfsustained or arrested spontaneously at some (possibly large) distance from the nucleation area. The transition from spontaneously arresting to self-sustained ruptures has been studied under slipweakening friction by Ampuero et al (2006), Viesca & Rice (2012) and Garagash & Germanovich (2012) in 2-D, and by Ripperger et al (2007) in 3-D. Our first goal is to determine the sufficient ('critical') conditions to initiate sustained ruptures, that is, ruptures on faults with uniform background stress that propagate indefinitely unless they encounter a high strength barrier.…”

Significance of the actual nonlinear slope geometry for catastrophic failure in submarine landslides

“…Indeed, the main challenge for SBP application lies in the practical difficulties of determination of the length of the initial weak zone. For triggers such as methane hydrate decomposition and local fluid fluxes, it is at least conceptually clear that their effect is spatially limited [21,39]. Reliable and accurate quantification of the spatial scale of this effect is, however, extremely difficult.…”

A phase coherence approach to identifying co-located earthquakes and tremor

“…What varies among the models and laboratory experiments is the magnitude and timing of that slip (Dieterich 1992;Ohnaka 1992;Campillo & Ionescu 1997;Ohnaka 2000;Ampuero et al 2002;Lapusta & Rice 2003;Rubin & Ampuero 2005;Ampuero & Rubin 2008;Rubinstein et al 2009;Fang et al 2011;Garagash & Germanovich 2012;Latour et al 2013;McLaskey & Kilgore 2013;Colombelli et al 2014;McLaskey & Lockner 2014). For instance, some models and observations predict that pre-seismic slip should be highly localized and release little moment (e.g.…”