Effects of tectonic evolution informed fault geometry on dynamic rupture propagation across step-overs: A case study of the Banquan pull-apart basin

Fault geometrical complexity is a first-order controlling factor on the extent of strike-slip fault surface rupture and earthquake magnitude, and step-over represents a key type of such complexity. The Banquan pull-apart basin along the Tanlu fault zone provides a natural example to investigate how tectonically evolved fault geometry influences dynamic rupture propagation across step-overs. We construct a 3-dimensional fault model that incorporates Y-shaped negative flower structure, connecting faults, and a sedimentary layer within the extensional step-over. The shallow fault geometry is constrained by surface geological observations, and the deep fault structure is informed by analogue experiments of pull-apart basin formation. Spontaneous coseismic dynamic rupture simulations are performed to examine the rupture behavior under these fault geometries. Our results show that when stress perturbation associated with stopping phases at the main fault termination is insufficient to trigger rupture on the secondary fault directly, the presence of connecting faults can act as a bridge to facilitate rupture propagation across the step-over. A deeper connecting fault can generate a stress shadow on the secondary fault, inhibiting local rupture propagation and potentially behaving as a barrier on the secondary fault, whereas shallow connecting faults have little influence on the rupture process. These findings provide insights into rupture jumping behavior in step-overs with similar fault structures and extend the existing interpretation of step-over triggering based on stopping phases with planar fault geometries.