Rheology, stress and aseismic slip at the subduction zone interface
From Cardiff University, UK
Hosted by Ágnes Király
Interseismic coupling at subduction zones, corresponding to whether the interface creeps aseismically or accumulates elastic strain that is released in earthquakes, varies significantly between regions. Interseismic coupling is commonly related to fault-zone scale rheological properties at the interface, however it can also be correlated with upper mantle scale dynamics. It is unclear how these processes and scales could be related. Exhumed samples of the subduction interface indicate that slip can be accommodated within mechanically heterogeneous material through varying styles of visco-brittle deformation. Numerical models are used to explore how the relative ratio of frictional to brittle deformation at the metre scale depend on shear zone properties and bulk stress state. At low shear stress, fracturing is localised and unlikely to develop into large slip surfaces. At high stress, the shear zone stress state is homogeneous and conducive to the formation of large frictional slip surfaces. Numerical subduction zone models are then used to demonstrate that shear stress at the interface can vary by >100%, depending on the rate of slab rollback and the transmission of slab pull forces, which influence the thickness of the interface shear zone. The thickness of visco-frictional subduction interface shear zones, and therefore the tendency for localised seismic slip to occur, may then depend on whether or not slabs extend to the lower mantle and have a history of rollback.