1. Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA

Correspondence to: Erik A. Kneller¹ Correspondence and requests for materials should be addressed to E.A.K. (Email: ekneller@umich.edu).

Abstract

Shear-wave splitting measurements above the mantle wedge of the Mariana¹ and southern Andean^{2, 3} subduction zones show trench-parallel seismically fast directions close to the trench and abrupt rotations to trench-perpendicular anisotropy in the back arc. These patterns of seismic anisotropy may be caused by three-dimensional flow associated with along-strike variations in slab geometry^{1, 2, 3, 4, 5}. The Mariana and Andean subduction systems are associated with the largest along-strike variations of slab geometry observed on Earth^{6, 7} and are ideal for testing the link between slab geometry and solid-state creep processes in the mantle. Here we show, with fully three-dimensional non-newtonian subduction zone models, that the strong curvature of the Mariana slab and the transition to shallow slab dip in the Southern Andes give rise to strong trench-parallel stretching in the warm-arc and warm-back-arc mantle and to abrupt rotations in stretching directions that are accompanied by strong trench-parallel stretching. These models show that the patterns of shear-wave splitting observed in the Mariana and southern Andean systems may be caused by significant three-dimensional flow induced by along-strike variations in slab geometry.

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