Review Article Global radially anisotropic mantle structure from multiple datasets: A review, current challenges, and outlook Sung-Joon Chang a,b, ⁎, Ana M.G. Ferreira a,c , Jeroen Ritsema d , Hendrik J. van Heijst e , John H. Woodhouse f a School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK b Dept. of Geophysics, Kangwon National University, Chuncheon, Gangwon-do 200-701, South Korea c Dept. of Earth Sciences, University College London, London WC1E 6BT, UK d Dept. of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA e Shell International Exploration and Production, Aberdeen AB15 9DL, UK f Dept. of Earth Sciences, University of Oxford, Oxford OX1 3PR, UK abstract article info Article history: Received 21 October 2013 Received in revised form 22 January 2014 Accepted 24 January 2014 Available online 1 February 2014 Keywords: Radial anisotropy Group velocity Crustal corrections Tomography LPO SPO 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. © 2014 Elsevier B.V. All rights reserved. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Theoretical background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Implications of radial anisotropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Upper mantle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.2. Transition zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.3. Lower mantle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Previous global studies of radial anisotropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Characteristic features of radial anisotropy at the regional scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.1. Central Pacific . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.2. East Pacific Rise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.3. Lithosphere–asthenosphere boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.4. D″ region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Comparisons of whole-mantle radially anisotropic models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7. Sensitivity kernels and synthetic tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Surface-wave sensitivity kernels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.2. Sensitivity to Moho depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.3. Sensitivity kernels of body-wave travel times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.4. Model resolution tests for surface-wave and body-wave data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8. Current challenges and new developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1. The influence of the crust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.2. New global radially anisotropic Earth model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Tectonophysics 617 (2014) 1–19 ⁎ Corresponding author at: Dept. of Geophysics, Kangwon National University, Chuncheon, Gangwon-do 200-701, South Korea. E-mail address: sjchang@kangwon.ac.kr (S.-J. Chang). 0040-1951/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.tecto.2014.01.033 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto