Study on rupture dynamics of branch fault system in 3D homogeneous and isotropic elastic medium by boundary integral equation method (BIEM)

Abstract:

We simulate rupture dynamics of branch fault system in 3D homogeneous and isotropic elastic medium by boundary integral equation method (BIEM). Numbers of simulations with varying tectonic stress σ_xx/σ_yy are modeled to investigate its effect on dynamic rupture of branch fault. It is found that when the main fault tectonic stress σ_xx/σ_yy is larger than a specified value (about 1.75), the branch fault rupture is more inclined to the compression fault, and rupture propagates on both the main and branch fault, while the final slip of branch fault is smaller than that of main fault. We also find when the main fault tectonic stress σ_xx/σ_yy  is smaller than a specified value (about 1.5), the branch fault rupture is more inclined to the extensional fault, and the rupture only propagates on the branch fault. Another interesting discovery is found that there is a second nucleation rupture on the main fault in 3D homogeneous and isotropic elastic medium, which is due to the stop phase of rupture on the branch. Our results show that the final slip of branch fault is proportional to the length of branch fault when the main fault tectonic stress σ_xx/σ_yy  is smaller than the specified value (about 1.5) on the extensional fault, which is larger than that of the main fault. So the occurrence of small earthquakes in the main fault may trigger a large earthquake on the branch fault. The effect of free surface on dynamic rupture of branch fault is also studied in this research.