Global radially anisotropic mantle structure from multiple datasets: A review, current challenges, and outlook

Since the 1960s seismologists have mapped anisotropy in the uppermost mantle, the mantle transition zone, and the D″ region. When combined with constraints from mineral physics and geodynamics, anisotropy provides critical information on the geometry of mantle flow. Here we review the theory, early work, recent tomographic models, and experimental constraints on radial anisotropy. We discuss current challenges in resolving radial anisotropy seismically. In particular, we show that it is highly beneficial to use multiple datasets in inversions for anisotropy, notably short-period group velocity data with strong sensitivity to the crust. We present a new whole-mantle model of radial anisotropy, based on surface-wave and body-wave travel time data, along with incorporated Moho perturbations. Our whole-mantle model shares common features with previous global models and is consistent with results from several high-resolution regional studies. •We review tomographic works for the estimation of radial anisotropy in the mantle.•Body and surface wave data are complementary to constrain radial anisotropy.•Crustal structure hampers the estimation of radial anisotropy.•Short-period group velocity data can constrain the crustal structure better.•We estimate crustal perturbations in our inversion by using group velocities.