Some effects of anisotropy on velocity contrasts between subducting lithosphere and overriding mantle

Abstract

We compute velocity anisotropy for three models of preferred crystal alignment due to finite strain in the mantle which, when juxtaposed with computed anisotropy in subducted lithosphere and neglecting other effects, give velocity contrasts that we compare with those observed. We find a strong dip dependence for computed velocity contrasts due to slow axis alignment in the overriding mantle perpendicular to the slab‐mantle interface. Moreover, for an isotropic mantle wedge or convergence‐parallel flow, it is difficult to produce greater velocity in the subducting slab than the overlying mantle for near‐vertical propagation even with high strain rates. We do, however, obtain positive contrasts using a dip axis‐parallel flow model, which is the only one that yields contrasts that approach observations from the Japan Trench.