The role of sediments on subduction dynamics and geometry: insights from numerical modeling

It is widely recognized that sediments play a key role for subduction. For example, sediments subducted along the shallow seismogenic plate interface are thought to influence seismic coupling and the occurrence of megathrust earthquakes, as well as the morphologies of accretionary prisms. Due to their weakening and/or lubricating effect, subducted sediments are also thought to promote faster plate speeds. However, global observations are not clear-cut on the relationship between the amount of sediments and plate motion. Here, we use 2D thermomecanical models to investigate how incoming plate sediments can influence subduction dynamics and geometry. We find that thick sediments can promote slower subduction due to an increase of the shear stress along the plate interface as the accretionary wedge gets wider, and a decrease of slab pull as more buoyant material is subducted. Our results also show that the larger interface shear stress and slab buoyancy due to thick sediments increase the slab bending radius. This study offers a new perspective on the role of sediments on large-scale subduction dynamics, suggesting that sediment buoyancy and wedge geometry might also affect plate motion and geometry.