Multicycle Dynamics of the Aksay Bend Along the Altyn Tagh Fault in Northwest China: 1. A Simplified Double Bend

摘要

I perform multicycle dynamic simulations of a restraining double bend that is simplified from the Aksay bend along the Altyn Tagh Fault in northwest China. The earthquake cycle includes a coseismic dynamic rupture phase and an interseismic stress loading and relaxation phase. The double bend fault system has two fault strands and each strand comprises a stem segment that strikes parallel to the maximum shear loading direction and a bend segment that deviates from the loading direction. I find that the restraining double bend is an effective barrier to dynamically propagating ruptures over multiple earthquake cycles, with a probability of rupture jumping from one strand to the other varying from 0% to 10%, depending on parameter values of the rate dependence of friction during the dynamic phase and the viscosity for stress relaxation during the interseismic phase. The critical condition for the primary rupture on the first strand to jump onto the second strand is that the preshear stress is close enough to the shear strength over a certain size of the fault patch on the second strand. These results on the simplified double bend provide important insights into rupture behavior of geometrically complex faults over multiple earthquake cycles in general and a reference to explore rupture behavior of the Aksay bend in particular.