Crustal anisotropy in the Ural Mountains Foredeep from teleseismic receiver functions

Radial and transverse teleseismic receiver functions (RFs) at GSN station ARU, in central Eurasia, display variation in back‐azimuth ψ consistent with a 1‐D anisotropic crustal structure. In a broad ψ range, the transverse RFs possess a strong phase at ∼5‐sec delay relative to direct P, with a polarity reversal at ψ ∼ 50°. The radial RFs peak at the transyerse‐RF polarity reversal for this converted phase. The first motion of the transverse RFs varies with ψ also, reversing polarity at ψ ∼ 345°. The azimuthal variation can be modeled by a 5‐layer velocity profile with substantial (15%) seismic anisotropy in both the lowermost crust and a low‐velocity surface layer. Assuming hexagonal symmetry, the lowermost crust has a tilted “slow” symmetry axis i.e. an oblate phase velocity surface. The strike of the axis is oblique to the north‐south Urals trend, but deviates <20° from the mantle fast‐axis inferred from SKS splitting. The magnitude and tilt of the model's anisotropy suggests that fine layering and/or aligned cracks augment mineral‐orientation anisotropy near the top and bottom of the crust.