Multicycle dynamics of nonplanar strike‐slip faults

Abstract

[1] We perform two-dimensional dynamic models of strike-slip faults with a change in strike (a bend) over multiple earthquake cycles to examine the long-term effects of nonplanar fault geometry. A viscoelastic model (a proxy for off-fault deformation and tectonic loading) is introduced for the interseismic process to avoid pathological stress buildup around the bend. A finite element method with an elastodynamic model is used to simulate dynamic earthquake ruptures. We find that stresses near the bend differ strongly from the regional stress field and that the fault develops a relatively steady state in which the stress level and the event pattern on the fault are stable. Reduced normal stress on the dilatational side and increased normal stress on the compressive side of the bend during dynamic ruptures result in the bend serving as an initiation and/or a termination point(s) for rupture. Typical events on such a fault consist of two classes: unilateral events that rupture only the favorable segment and bilateral events that rupture the favorable segment and part of or the entire unfavorable segment. In the latter class of events, a time delay in rupture around the bend results from a high yield stress on the compressive side of the bend. Other effects of the bent fault geometry include higher displacement on the inward wall than on the outward wall, higher slip on the more favorable segment than on the less favorable segment, and a large slip velocity on the compressive side of the bend.

Finite Element Modeling of Branched Ruptures Including Off-Fault Plasticity

“…If contact across the fault is later reestablished (not a phenomena observed in most simulations), the evolution of friction resumes from its prior, potentially weakened value. This formulation does not take important dynamic weakening effects into account, but has successfully been used to model earthquake rupture in single fault models (e.g., Duan and Oglesby, 2005), fault step models (e.g. Harris and Day, 1999) and branched geometries (e.g., Aochi et al, 2000;Kame et al, 2003;Templeton et al, 2009).…”

“…The Traction at Split-Nodes (TSN) procedure is implemented in many numerical models (e.g., Duan and Oglesby, 2005;Day et al, 2005;Ma and Archuleta, 2006). This method, discussed in Andrews (1999), is based on the assumption of two nodes, one on each side of the fault, which only slide past one another and do not open.…”

Initiation propagation and termination of elastodynamic ruptures associated with segmentation of faults and shaking hazard

“…A number of models have examined individual elastodynamic events on nonplanar fault geometries, but not populations of events [Harris et al, 1991;Kame and Yamashita, 1997;Bouchon and Streiff, 1997;Aochi et al, 2000]. Two modeling efforts have looked at event sequences on an individual complex fault [Mora and Place, 1999;Duan and Oglesby, 2005]. Our work is new in providing long catalogues of elastodynamic ruptures on geometrically complex fault systems [Shaw, 2004a[Shaw, , 2004b.…”

A domain decomposition approach to implementing fault slip in finite‐element models of quasi‐static and dynamic crustal deformation

“…For example, Duan and Oglesby [2005] simulated multiple earthquake cycles on a fault with a bend to capture the spatial variation in the stress field around the bend, which they found to have a strong role in determining whether a rupture would propagate past the bend. By spinning up the model over many earthquake cycles, they obtained a much more realistic stress field immediately prior to rupture compared with assuming a simple stress field or calculating the stress field from a static analysis.…”