On the supershear transition in heterogeneous media

During an earthquake, frictional rupture fronts mainly propagate at subshear speedalong tectonic faults. However, evidences of supershear propagation have been re-ported in several occasions. Contrarily to subshear, supershear rupture results in highstresses and particles velocities far away from the interface.Earthquakes are generally represented as mode II fracture. If the in plane shearload excess a critical value, a crack propagating initially at subshear velocity will tran-sition to intersonic one through the Burrdige-Andrews mechanism. This transition hap-pens at a defined crack size for homogeneous problem. However, realistic interfacessuch as geological faults involve heterogeneities, which affect this mechanism. Both inand out plane heterogeneities can facilitate this transition via the emission and reflec-tion of elastic waves. Using numerical methods, it has been shown how the presenceof in plane successive weak and strong stripes eases the supershear transition. Frontinteraction with heterogeneities matters if their size is comparable to the process zonesize, in which damage is localized ahead of the crack tip.In this study, we extend these earlier works to the general case of a dynamic crackpropagating along a 2D plane, with various patterns of heterogeneities. Using an elas-todynamic boundary integral formulation coupled with a cohesive zone model, we sys-tematically study the interaction of the crack front with the microstructure. Occurrenceof supershear transition is extensively investigated for both organized and randomizedheterogeneous pattern.