Using three-dimensional numerical models, the authors investigate how a buoyant ribbon of thickened oceanic crust colliding with a subduction zone disturbs stress and strain within the subducting slab and the surrounding plates. They find that the angle of collision creates compartmentalised zones of high and low strain rate around a region of strong vorticity, and that collision-related stresses are comparable in magnitude to those from buoyancy variations and slab pull. These results suggest that rapid strain rate changes caused by ribbon collision can explain seismicity gaps along collisional margins often attributed to slab tears.
Abstract. Ribbon collision is a process that can rapidly disturb the symmetry of subduction zones. Previous studies have demonstrated how ribbon collision causes rotation at the surface and contortion in the slab, but have only focused on the surface kinematics. We use three‐dimensional mechanical models to investigate how ribbon collision perturbs the strain and stress field at the surface, the slab interior, and intraplate force balance. In our numerical simulations, we vary the angle between the trench and the ribbon to explore the slab response to ribbons colliding at different orientations. Our numerical simulations show that ribbon collision causes significant heterogeneity of stress, strain rate and vorticity near the surface and the slab itself. Slab deformation shows compartmentalization into low and high strain rate regions around a high vorticity zone, with strain rate variations of up to an order of magnitude occurring in the along‐strike and down‐dip directions. In the context of our idealized oceanic‐continental subduction system, the simulations show that intra‐plate stresses are affected to a similar degree by buoyancy contrasts (i.e., gravitational potential energy variations), slab‐pull and ribbon collisions. This partitioning allows for significant heterogeneity in the intra‐plate stress regime. This work highlights how the rapid changes in strain rate within the slab, caused by ribbon collision, can explain the seismicity gaps observed in collisional margins, which are often interpreted as slab‐tears.
