Chapter 8 Rupture Dynamics on Bimaterial Faults and Nonlinear Off-Fault Damage

Abstract

We review recent progress in our understanding of the generation mechanism of off-fault damage and rupture dynamics on a bimaterial interface. Although an earthquake fault is traditionally modeled as a planar fault in an isotropic homogeneous medium, it is becoming increasingly clear that such an approach is inadequate for a deep understanding of earthquake rupture dynamics. In fact, field observations indicate the existence of tensile microfractures and shear fault branches that surround earthquake faults; such fractures generally define the damage zone formed near earthquake faults. In spite of its importance, the modeling of damage is not straightforward because microfractures and shear branches are densely distributed in the damage zone and their interactions cannot generally be neglected. However, recent years have brought some progress in the study of this area. It is also known that a geological fault with long slip history is likely to occur on a bimaterial interface. If a fault constitutive friction law dependent on the normal stress is assumed as in a Coulomb friction law, the rupture occurring on a bimaterial interface is enriched by the coupling between slip and normal stress. Although the bimaterial effect on dynamic earthquake rupture is still in debate partly because many factors seem to affect rupture dynamics, active study is now being carried out.