Azimuthal and radial anisotropy in the upper mantle from global adjoint tomography

Earth’s upper mantle and lithosphere show significant evidence for anisotropy related to deformation and composition. First-generation GLAD (GLobal ADjoint) models (GLAD-M15 (Bozdag et al. 2016), GLAD-M25 (Lei et al. 2020), GLAD-M35 (Cui et al. submitted)) are radially anisotropic in the upper mantle. Starting from GLAD-M25, we performed 25 conjugate gradient iterations and constructed model GLAD-M50-AZI by including azimuthal anisotropy in the parameterization of the inverse problem. We inverted azimuthally anisotropic normalized parameters Gc’ and Gs’ simultaneously with vertically and horizontally polarized shear waves beta_v and beta_h, respectively. Due to our parameterization, our data set consists of only minor- and major-arc Rayleigh and Love waves from 300 globally distributed earthquakes. GLAD-M50-AZI captures plate motions globally well, which are also supported by the transverse isotropy, specifically at the subducted slabs and mid-ocean ridges. Furthermore, it approaches continental-scale resolution in regions with good data coverage depicting smaller-scale tectonic and flow patterns, giving us a chance to have a more detailed and unified view of the anisotropy globally. In the next step, we explore how anisotropy derived from seismic tomography compares to geodynamical modeling observations to have better insight into mantle dynamics. We perform numerical simulations to compute synthetic seismograms and full-waveform inversion on Texas Advanced Computing Center’s Frontera system.