Effects of a Barrier on Earthquake Ruptures: Stop or Supershear?

Abstract:

Geometrical and frictional heterogeneities, such as kinks/bends and stress/friction anomalies, are commonly observed on seismogenic faults. However, whether they may nucleate, promote, or stop earthquake ruptures remains controversial. Here we investigate the effects of fault heterogeneity on earthquake ruptures through dynamic rupture simulations on a “slip-weakening” fault. We demonstrate that such heterogeneity can act as a barrier to earthquake ruptures, depending on the effective normal stress and geometry associated with the heterogeneity. Furthermore, we find that such barrier effect is most prominent when the barrier sits at an intermediate range of the barrier-nucleation distances. However, instead of stopping ruptures, the barrier may also induce ruptures that propagate faster than shear wave velocity (supershear). The barrier-induced supershear ruptures may be transient and the durations are proportional to the reduction in main rupture speed caused by the barrier. We also demonstrate that the emergence of supershear ruptures can be delineated by two linear boundaries, which are related to the barrier size and the barrier-nucleation distance. Considering such a barrier in long-term earthquake cycles, we observe that the barrier can also turn into asperities experiencing large coseismic slip. These results suggest that a strong barrier patch on the fault may not necessarily stop coseismic ruptures and thus reduce the maximum size of earthquakes. Instead, the barrier could experience large coseismic slip and/or induce supershear ruptures that play important roles in near-field ground shaking and damage.