[1] Seismic hazard analysis relies on the ability to predict whether an earthquake will terminate at a fault tip or propagate onto adjacent faults, cascading into a larger, more devastating event. While ruptures are expected to arrest at fault discontinuities larger than 4-5 km, scientists are often puzzled by much larger rupture jumps. Here we show that material properties between faults significantly affect the ability to arrest propagating ruptures. Earthquake simulations accounting for fault step-over zones weakened by accumulated damage provide new insights into rupture propagation. Revealing that lowered rigidity and material interfaces promote rupture propagation, our models show for the first time that step-overs as wide as 10 km may not constitute effective earthquake barriers. Our results call for re-evaluation of seismic hazard analyses that predict rupture length and earthquake magnitude based on historic records and fault segmentation models.

SUMMARY Numerical modelling of dynamic rupture is conducted along faults separating similar and dissimilar materials. Supershear transition is enhanced in the direction of slip of the stiffer material (the negative direction) due to the bimaterial effect whereby a decrease in normal stress in front of the crack tip supports yielding ahead of the rupture. In the direction of slip of the more compliant material (the positive direction), an increase in normal stress ahead of the rupture tip delays or prevents the supershear transition, whereas the impact of the bimaterial effect on subshear ruptures is to promote rupture in the positive direction due to the tensile stress perturbation behind the rupture tip in this direction. We demonstrate that the material contrast and the parameter S control whether the transition from sub‐ to supershear velocity (supershear transition) is smooth or follows the Burridge–Andrews mechanism. Supershear transition along interfaces separating dissimilar materials is possible for higher values of the parameter S than supershear transition along material interfaces separating similar materials. The difference between pulse‐like and crack‐like rupture is small with regard to the supershear transition type.

SUMMARYDynamic simulations of homogeneous and bi-material fault rupture are modeled using different loading approaches. We demonstrate that a numerical method of quasi-static loading is capable of immediately loading bi-material interfaces to rupture without the iteration over multiple time steps. We show that our method is a computationally inexpensive approach to tectonic loading and is capable of loading a fault to failure. We observe earthquake rupture speed, slip distances and slip rates for homogeneous and bi-material faults for various applied stresses, friction properties and material contrasts across the bi-material interface. We comment on causes for unilateral rupture growth. The results are consistent with experimental results and highlight the importance of material heterogeneity in determining the rupture characteristics of earthquake faults.

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