Normal stress perturbations accompany propagating mode II rupture along an interface separating materials of contrasting elastic compliance. The extent to which those perturbations may produce significant, observable rupture asymmetries (i.e., final slip distribution heavily weighted toward a preferred propagation direction) in earthquakes is uncertain, but previous numerical simulations predict such asymmetry when frictional resistance is velocity dependent, with sufficient post-rupture re-strengthening to produce pulse-like rupture. We show, by numerical simulations in 3D, that purely geometrical effects leading to pulse-like rupture can also induce strong asymmetries (and under very limited conditions can even evolve into strictly unilateral rupture), even when frictional rate dependence is neglected. The effect is studied here in a context that can only apply to strike-slip earthquakes large enough to rupture the entire seismogenic thickness, but the results suggest that other geometrical effects leading to pulse-like rupture will interact with a compliance contrast in a similar manner. Copyright 2009 by the American Geophysical Union.