Mapping P-wave Azimuthal Anisotropy near the Core-Mantle Boundary using Novel Observations of Core-Diffracted waves PcSdiff

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While the Earth's surface marks the boundary between the atmosphere and the solid earth, the core-mantle boundary (CMB) separates the solid mantle from the liquid core, modulating the loss of heat and driving the earth's dynamo and magnetic field.Constraining seismic anisotropy in the CMB region is challenging. Previous results on S wave anisotropy are subjected to some limitation in geographical sampling, azimuthal coverage or/and proper correction of upper mantle seismic anisotropy, which is not trivial. None of previous studies, neither in isolation or in combination, regional or global scale, has yielded any estimate of P-wave azimuthal anisotropy in the D'' layer. We do NOT know P wave anisotropy property of ultra-low velocity zones (ULVZs), large low-velocity provinces (LLVPs) or slab graveyards.We will use novel observations of core-diffracted PcSdiff wave in the radial P wave receiver function stacks to constrain P wave azimuthal anisotropy in the core-mantle boundary, with a particular focus on the regions of possible slab graveyard, ULVZs and the base of LLVPs. These renewed descriptions of P wave anisotropy models will be used to explore outstanding questions including the rheology or the deformation mechanism, the mantle flow patterns near the core-mantle boundary and the nature of LLVPs and ULVZs.A series of outstanding questions can be much better addressed with our new seismic observations:What's the rheology and deformation mechanism operating in the D'' layer? How did the slab graveyard, LLVPs and ULVZs deform and their anisotropy properties? Are LLVPs and ULVZs compositional distinctly from the rest of the D'' layer?Is the deformation accommodated by bridgmanite, post-perovskite or secondary minerals such as ferropericlase and calcium-perovskite? Is the dislocation creep, responsible for upper mantle seismic anisotropy, operating in the D'' layer?These unprecedentedly rich observations will provide renewed constraints on fundamental processes relevant to the Earth's interior and evolution.