Constraining fault constitutive behavior with slip and stress heterogeneity

Abstract

[1] We study how enforcing self-consistency in the statistical properties of the preshear and postshear stress on a fault can be used to constrain fault constitutive behavior beyond that required to produce a desired spatial and temporal evolution of slip in a single event. We explore features of rupture dynamics that (1) lead to slip heterogeneity in earthquake ruptures and (2) maintain these conditions following rupture, so that the stress field is compatible with the generation of aftershocks and facilitates heterogeneous slip in subsequent events. Our three-dimensional finite element simulations of magnitude 7 events on a vertical, planar strike-slip fault show that the conditions that lead to slip heterogeneity remain in place after large events when the dynamic stress drop (initial shear stress) and breakdown work (fracture energy) are spatially heterogeneous. In these models the breakdown work is on the order of MJ/m 2 , which is comparable to the radiated energy. These conditions producing slip heterogeneity also tend to produce narrower slip pulses independent of a slip rate dependence in the fault constitutive model. An alternative mechanism for generating these confined slip pulses appears to be fault constitutive models that have a stronger rate dependence, which also makes them difficult to implement in numerical models. We hypothesize that self-consistent ruptures could also be produced by very narrow slip pulses propagating in a self-sustaining heterogeneous stress field with breakdown work comparable to fracture energy estimates of kJ/M 2 .Citation: Aagaard, B. T., and T. H. Heaton (2008), Constraining fault constitutive behavior with slip and stress heterogeneity,

The 2010 Qinghai, China, Earthquake: A Moderate Earthquake with Supershear Rupture

“…The damage seems to have been unusually intense in the Yushu area, considering the relatively low population density and maximum surface ruptures of 0.5-1.8 meters . Numerical modeling shows strong focusing and other effects of energy at the rupture front that can intensify the ground motions to varying degrees (Aagard and Heaton, 2008;Bizzarri et al, 2010;Xu et al, 2010), so the supershear rupture may have made a significant contribution to the severe damage caused by the Qinghai earthquake.…”

Geologic evidence for multiple slip weakening mechanisms during seismic slip in crystalline rock

“…For example, the observations presented in this study document the structure of seismogenic faults at the meter to tens of meters scale, whereas the inversion of seismic data typically has a minimum spatial resolution of hundreds of meters. However, Aagaard and Heaton [2008] point out that frictional stress changes occur over a few milliseconds, suggesting that corresponding slip weakening distances, or breakdown zone widths, might be of the order of millimeters. The relatively short length scales exposed in the field are therefore of relevance to the rupture process.…”

Evidence for universal earthquake rupture initiation behavior

“…Smith & Heaton 2011), as well as the dynamics in the ongoing rupture energy budget (e.g. Aagaard & Heaton 2008;Elbanna & Heaton 2012), all of which render a deterministic rupture development improbable.…”