Influence of pre-stress conditions in 2D plane strain simulations of a dynamic rupture with off fault damage

Understanding the mechanical properties of the off-fault medium and its interactions with earthquake rupture is essential for a better understanding of the behavior of fault zones. In this framework, two-dimensional, plane strain models are often used to investigate the interplay between seismic rupture propagation and inelastic deformation in the damage zone. The role of pre-stress conditions for faulting and damage has been studied, in particular the influence of Y, the angle between the largest principal stress and the fault strike. However, in plane strain conditions, the out-of-plane stress is often ignored when setting up the initial stress field, and its influence on dynamic rupture and stress evolution has not been inferred. In this study, we explore the role of the out-of-plane pre-stress for a 2D in-plane model in plane strain conditions. We model a 1D right-lateral, strike-slip vertical fault featuring slip-weakening friction law. We first demonstrate theoretically that if the out- of-plane stress is not considered properly in the initial stress field, pre-stress conditions may not correspond to actual strike-slip faulting. We then investigate how changing the initial stress field can influence the rupture and the stress evolution in the off-fault medium. Our results show that if it does not influence significantly the rupture dynamics, the out-of-plane stress is essential in controlling the evolution of the off-fault medium, especially the localization and extend of areas affected by plastic yielding. Therefore, our results demonstrate the importance of considering properly the initial out-of-plane stress to infer the extend, magnitude and distribution of damage in 2D plane strain simulations with off fault plastic deformation.