Confrontation of mantle seismic anisotropy with two extreme models of strain, in central Asia

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Abstract
Although most authors agree that convergence is accommodated by a large shortening in Asia, two radically different modes of shortening have been put forward. In one approach, the mechanism of shortening is considered to be homogeneous, producing diffuse deformation in the crust and the mantle. In the second one, motions are localized along faults which are supposed to extend into deep lithospheric shear zones, inducing a heterogeneous deformation pattern. Seismic anisotropy is one observable manifestation of large scale deformation. Large scale seismic anisotropy field are inferred from the two extreme competing models. 3D‐mapping of anisotropy, inferred from surface waves, reveals a better coherence on average with filtered heterogeneous strain models between 100 and 200 km depths. It suggests a strong coupling between surface and deep motions down to at least 200 km. At larger depths, the coherence with homogeneous strain models suggests that mantle flow becomes more homogeneous.