Dynamic simulations of earthquakes on dipping faults show asymmetric near-source ground motion caused by the asymmetric geometry of such faults. The ground motion from a thrust or reverse fault is larger than that of a normal fault by a factor of 2 or more, given identical initial stress magnitudes. The motion of the hanging wall is larger than that of the footwall in both thrust (reverse) and normal earthquakes. The asymmetry between normal and thrust (reverse) faults results from time-dependent normal stress caused by the interaction of the earthquake-generated stress field with Earth's free surface. The asymmetry between hanging wall and footwall results from the asymmetric mass and geometry on the two sides of the fault.

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[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.

[1] We combine a viscoelastic model for the interseismic process and an elastodynamic model for the coseismic process to explore the dynamics (over multiple earthquake cycles) of two parallel strike-slip faults embedded in a two-dimensional full space. The step over fault geometry results in a buildup of heterogeneous fault stress near the step over. This heterogeneous stress accumulates at the early stage of the evolution of the fault system, and finally stabilizes after a number of earthquake cycles. The heterogeneity in fault stress varies with the geometrical parameters (e.g., width and along-strike overlap/ gap) of the step over, as well as the rupture history of the fault system. This heterogeneous fault stress from previous earthquakes has significant effects on earthquake rupture initiation, propagation, and termination. The locations with a low normal stress level near a step over are favorable points for earthquake initiation. Rupture can jump a 4 km wide compressional step over and a 8 km or wider dilational step over if the fault system has historically experienced many earthquakes. A young step over with less induced heterogeneity allows rupture to jump only smaller step over widths. These results may have important implications for seismic hazard analysis in areas where segmented strikeslip faults predominate, particularly for estimating maximum earthquake potential.

Recent two-dimensional dynamic simulations of dip-slip faulting (Niel