Rupture phase diagrams for a planar fault in 3-D full-space and half-space

In this study, we have systematically investigated the influence of the parameters of the slip-weakening law and the size of nucleation asperity on dynamic rupture of a planar fault in full-space and half-space using the boundary integral equation method, in particular, the occurrence conditions for subshear (or sub-Rayleigh for strike-slip rupture) and supershear ruptures. Besides the well-known rupture styles of subshear (or sub-Rayleigh) and supershear, we defined a new kind of rupture style in this study, termed the 'self-arresting rupture', for which the rupture process can be autonomously arrested by itself without any outside interference (e.g. a high strength barrier). Based on the vast number of simulations, we obtained rupture phase diagrams for strike-slip and dip-slip ruptures vertically and obliquely embedded in half-space and full-space with different buried depths. The rupture phase diagram clearly illustrates the occurrence conditions of three kinds of rupture styles and the transitions between them. In full-space, the supershear transition is sensitive with the fault width. Owing to the influence of the free surface, the rupture in half-space becomes much more complicated comparing to the one in full-space. For a strike-slip fault with zero buried depth, all ruptures that occur within the parameter range for sub-Rayleigh ruptures in full-space case become supershear ruptures. This means that as long as a rupture is able to grow incessantly, it will always evolve into a supershear rupture. For dip-slip faults, however, ruptures will always propagate with subshear speed, although slip rate could be almost twice that of a strike-slip fault. Although the influence of the free surface is strong, it is limited to very shallow ruptures (i.e. buried depth < 1 km). The rupture phase diagram discussed in this study could provide a new insight on earthquake rupture mechanics.