S41D-06:
Global Radially Anisotropic Whole-Mantle Structure from Multiple Datasets
Thursday, 18 December 2014: 9:15 AM
Ana MG Ferreira, University College London, Earth Sciences, London, United Kingdom, Sung-Joon Chang, Kangwon National University, Chuncheon, South Korea, Jeroen Ritsema, Univ Michigan, Ann Arbor, MI, United States, Hendrik Jan van Heijst, Shell International, Rijswijk, Netherlands and John H Woodhouse, University of Oxford, Oxford, 0X1, United Kingdom
Abstract:
When detected, seismic anisotropy can potentially be an indicator of mantle flow and thus can help us discriminating different geodynamical processes and competitive thermo‐chemical convective models of the Earth’s interior. However, the imaging and interpretation of global anisotropy is challenging. For example, Ferreira et al. (2010) reported that a data misfit reduction of only around 2% is obtained when lateral variations in radial anisotropy in global tomographic inversions are included compared to inversions only allowing 1-D variations in anisotropy. This small misfit reduction is comparable to the effect on data misfit of using different crustal corrections, thereby indicating a strong influence of the crust in the models. We discuss new high-resolution (degree 35) inversions for models of 3-D isotropic and radially anisotropic shear-wave velocity in the whole mantle incorporating crustal thickness perturbations as model parameters in the inversions to properly consider crustal effects. We use a massive data set of over 43 million surface-wave and 420,000 body-wave measurements from several published studies with complementary sensitivities to Earth’s structure. It includes relatively short period group velocity data down to T~16 s that constrain crustal thickness. We find that the various datasets used are highly complementary, allowing us to achieve good resolution in isotropic structure in the whole mantle and throughout the upper ~1,400 km of the mantle for anisotropic structure. Our images of isotropic structure share common features with previous 3-D S-velocity models, such as high-velocity anomalies beneath cratons and subduction zones. The anisotropic models are consistent with various persistent features in previous regional studies of radial anisotropy and show some peculiar features near subduction zones in the transition zone. We discuss these features and their potential implications, as well as the challenges and outlook for the next generation of global 3-D anisotropy models.
