Controlling factors analysis of dynamic rupture propagation simulation of curved fault based on Boundary integral equation method

Earthquakes seldom rupture along single planar faults. Instead, there exist geometric complexities, including fault bends, branches and step overs, which affect the rupture process, nucleation and arrest. In order to understand the influences of nonplanar fault geometry on the earthquake rupture, dynamic numerical simulation provides a new insight. Boundary integral equation method (BIEM) is an appropriate method to model the dynamic rupture process of complex fault geometries, which simplifies the problem and requires small resources in computation by only discretizing the fault surfaces. In addition, it is easy to consider the singularity at the tip of crack using BIEM. When spatially discretizing the fault models, the rectangle meshes are commonly used, however, it is more detailed to describe the nonplanar fault geometries with triangle meshes. It has been recognized that an exponentially growing numerical oscillation resulting from spatiotemporal discretization is well known in the BIEM community. Therefore, an appropriate and optimum combination of space grid and time intervals is very important, which can suppress the oscillation and unstability to some extent. Here, the Courant-Fridrichs-Lewy condition is utilized to achieve the target. In this study, the relationship determined by CFL condition is Delta t <= root 2 Delta x/6V(p). In this paper, the stress Green's functions for a constant slip rate on a triangular fault are calculated. Theorectially, the mechanics of earthquake rupture process can be regarded as a transformation from static friction to dynamic one. For the dynamic rupture modeling, friction criterion plays a very important role. Because we only focus on the rupture propagation and neglect the nucleation and cessation, slip weakening friction law is applied in our study. Nonplanar fault geometries include many types as mentioned above, and here we just take the curved faults with different bending angles as examples to study the influences of fault geometries on the rupture propagation. After modeling, it is found whether rupture can continue to propagate after curventure part is controlled by many factors, such as bending angles, initial stress in and out of the asperity, the radius of the asperity, slip weakening distance and so forth. Simulation results show that the higher the initial stress in and out of the asperity is, the easier the rupture propagates. And the larger the radius of the asperity or the smaller the slip weakening distance is, the easier the rupture propagates beyond the bend part. Given the same initial conditions, when the inclination angle is bigger, it has more obvious inhibition effect and can be taken as a barrier. However, the curved fault with small inclination angle has similar rupture propagation characteristics, and does not show obvious inhibition effect.