Multicycle dynamics of nonplanar strike-slip faults

Abstract

We perform two-dimensional dynamic models of strike-slip faults with a change in strire (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. Copyright 2005 by the American Geophysical Union.