Splitting predictions for synthetic anisotropy models in the lowermost mantle beneath a slab

In this multi-disciplinary study we test the complex seismic anisotropy resulting from deformation of a subducting slab onto the core-mantle boundary for different mineralogical compositions. Tracers in a 3D geodynamical model with a subducting slab track the velocity gradient tensor along the slab. This information is fed into a viscoplastic polycrystal plasticity model along with major mineral components and different assumptions for their active slip systems and elastic properties. We test models of perovskite and postperovskite, assuming different dominant slip systems. Next, we analyze the resulting radial anisotropy as well as shear wave splitting in directions along and across the slab. Postperovskite with a main slip plane of (001) results in consistent radial anisotropy for S waves (VSH>VSV), as well as an opposite signature in radial anisotropy for P waves. A main slip plane of (010) in postperovskite also results in consistent shear wave radial anisotropy, but is weaker in strength. Shear wave splitting with suitable crossing rays can further distinguish between these compositional models. The model with postperovskite with a main slip system along (001) shows strong variation in splitting parallel and orthogonal to the subducting slab, while other models show similar splitting.