Numerical simulation of spontaneous rupture processes on two non-coplanar faults: the effect of geometry on fault interaction

Analyses of earthquake sources have revealed that the earthquake rupture pr ocess is complex and that the rupture does not occur on a single plane. Ear thquake faults are often composed of several subfaults, and rupture propaga tion tends to decelerate or terminate at places where the fault strike chan ges. These observations imply that fault geometry, including fault steps an d fault strike change, plays an important role in earthquake rupture comple xity. In this paper, we calculate the spontaneous rupture processes of two non-coplanar faults in 2-D in-plane problems, attempting to clarify the eff ect of fault geometry. We consider two simple models-models in which two fa ults are either parallel or perpendicular to each other. We calculate spont aneous rupture propagation on the faults by a finite difference method, and we then compare the results. In our simulations, rupture initially grows o n the main fault, and stress perturbation from the main rupture then trigge rs rupture on the secondary fault. Propagation of the main-fault rupture co ntrols a spatio-temporal pattern of stress difference in the uniform elasti c medium, which determines the rupture process of the secondary fault. The rupture propagation and termination of the secondary fault are significantl y different between the two models. The difference is obvious when rupture of the main fault is arrested and the secondary fault is located near the a rrested end of the main fault. When the secondary fault is parallel to the main fault, rupture can propagate ahead on the secondary fault. However, wh en the secondary fault is perpendicular to the main fault, rupture is eithe r not triggered on the secondary fault, or soon terminates if triggered. Th is variation of the rupture process implies that: fault interaction, depend ing on geometry, can explain the termination and change of rupture at place s where the fault strike varies. This shows :the importance of the fault ge ometry in studying spontaneous dynamic rupture processes.