Development of mantle seismic anisotropy during subduction-induced 3-D flow

The dynamics of subduction can be indirectly constrained by studying the induced mantle flow. However, inferring the circulation of the mantle around subducting plates from the interpretation of shear wave splitting patterns remains elusive. We calculated the strain-induced lattice preferred orientation (LPO) developed in 3-D models of subduction where retreat motions are maximized and found that in the mantle layer entrained with the downgoing slab the seismic anisotropy is trench-perpendicular, and becomes trench-parallel deeper, where the toroidal flow accommodates slab retreat. Synthetic SKS splitting shows that in the fore-arc slab rollback favors trench-parallel polarization of the fast shear wave component, while plate advance enhances trench-perpendicular seismic anisotropy.