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

地球表面是大气和固体地球的分界线，而核幔边界（CMB）将固体地幔和液体地核分隔开来，调节着热量的损失，驱动着地球的发电机和磁场，在CMB区域限制地震各向异性是一个挑战。以往关于S波各向异性的研究结果在地理采样、方位角覆盖和上地幔地震各向异性校正等方面存在一定的局限性。以前的研究，无论是孤立或组合，区域或全球尺度，都没有产生任何估计的P波方位各向异性的D“层。我们不知道超低速带（ULVZ）、大低速区（LLVP）或板片墓地的P波各向异性特征，我们将利用径向P波接收函数叠加中的新的核衍射PcSdiff波观测来约束核幔边界的P波方位各向异性，特别关注可能的板片墓地、ULVZ和LLVP基底区域。这些P波各向异性模型的新描述将被用来探索悬而未决的问题，包括流变学或变形机制，核幔边界附近的地幔流动模式以及LLVPs和ULVZ的性质。一系列悬而未决的问题可以更好地解决我们的新地震观测：D“层的流变学和变形机制是什么？板片墓地、LLVPs和ULVZ是如何变形的及其各向异性特性？LLVPs和ULVZ的成分与D“层的其余部分不同吗？变形是由硼镁石、后钙钛矿还是次生矿物如铁方镁石和钙钛矿调节的？造成上地幔地震各向异性的位错蠕动是否在D“层中起作用？这些前所未有的丰富观测将为与地球内部和演化有关的基本过程提供新的限制。

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.