Dynamic rupture processes on two parallel faults connected by a different striking segment

Earthquake faults sometimes have bends, and the bends act as geometrical barriers and initiation points of earthquake rupture. It is important to predict whether a rupture can propagate beyond bends, but the rupture process depends on not only fault geometry but stress condition. In this study, we investigate a rough standard whether two fault segments connecting by a short and slight bending segment rupture simultaneously, based on dynamic rupture simulations using several fault models with bends and stress conditions. We put a vertical strike-slip fault in a 3-D, semi-infinite, homogeneous, isotropic, and linear elastic medium. The fault consisted of two parallel segments and a different striking segment connecting the segments. The whole length and width of the fault are 60 km and 15 km, respectively. The medium is subjected to principal compressional stresses proportional to depth. We examine several stress conditions with different angles between the part of the fault with the hypocenter and the maximum principal compressional stress axis. The initial stresses on a bending segment therefore depend upon the bending angle and the stress condition. We use a finite-difference method by Kase and Day (2006) with slip-weakening friction law. In large strike difference cases, rupture velocity on the connecting segment decelerates because of negative stress drop on the segment. Larger negative stress drop caused by higher strike difference needs shorter length of the connecting segment for rupture termination. On the other hand, effects of an existence of the connecting segment can be ignored when the connecting segment is short or the difference of strikes is small. Under all stress conditions used in this study, a rupture propagates beyond less than 1 km length connecting segment, and the connecting segment with less than 5 degrees strike difference hardly affects rupture propagation.