3D data sensitivities of seismic phases to the upper-most outer core and D’’ region

Abstract:

It is essential to have higher-resolution images of the upper-most outer core to gain better insight into the region's geodynamical processes and thermo-chemical structure. However, the potential trade-off between the mantle, the D" region, and the outer core, as well as the effect of mantle corrections, are still not well understood. We investigate the effect of the mantle, and crustal complexities on seismic phases sample the upper-most outer core and the D" region, i.e., Sdiff, ScS and SmKS, by computing 3D data sensitivities using the adjoint method. We compute 3D synthetic seismograms and associated adjoint sensitivity kernels using the 3D global wave propagation solver SPECFEM3D_GLOBE (Komatitsch and Tromp 2002) package, including the full complexity of wave propagation. The simulations are systematically performed for 1D and the recent global adjoint tomography models such as GLAD-M15 (Bozdag et al. 2016) and GLAD-M25 (Lei et al. 2020) using Oak Ridge National Laboratory's IBM AC922 "Summit" system. We also demonstrate different measurement techniques such as cross-correlation traveltimes, waveform differences, and their double-difference versions to construct a strategy for simultaneous full-waveform inversion of the D" region and the outer core.