Effects of coseismic megasplay fault activity on earthquake hazards: Insights from discrete element simulations

Abstract

Deep-water megasplay faults may promote or limit earthquake rupture and tsunami genesis. To better understand how megasplay faults affect earthquake rupture and associated tsunami potential, we use the Discrete Element Method (DEM) to model the upper plate as a wedge that is partitioned into a seismic (velocity-weakening, VW) inner wedge and an aseismic outer (velocity-strengthening, VS) wedge, combined with a splay fault rooting at the decollement. We examine the effects of the width of the outer (VS) wedge, as well as the dip and friction along the splay fault during earthquake rupture. Our results suggest that along-strike variations in the width of the VS outer wedge along the Chile Margin may play a key role in splay fault activity in the ruptured segment of the 2010 Maule earthquake. In addition, our model fit to the published slip distribution for the 2010 Maule earthquake suggests that megasplay fault activation did not significantly impact earthquake size along the south-central Chile Margin. In contrast, our model fit to the slip distribution for the 2011 Tohoku earthquake shows that megasplay fault reactivation may have moderately affected earthquake coseismic rupture. Splay faults can slip coseismically, contributing to associated tsunamis. However, the presence of a VS outer wedge is the predominant constraint on rupture size and tsunami generation.