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

虽然地球表面标志着大气和固体地球之间的边界，但地核-地幔边界（CMB）将固体地幔与液体地核分开，调节热量的损失并驱动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。以往的S波各向异性研究结果在地理采样、方位角覆盖或上地幔地震各向异性校正等方面存在一定的局限性，这是不容忽视的。以前的研究，无论是单独的还是联合的，区域或全球尺度，都没有对D”层的纵波方位各向异性做出任何估计。超低速带（ULVZs）、大低速省（LLVPs）或平板墓地的纵波各向异性特性尚不清楚。我们将利用径向P波接收函数栈中核衍射PcSdiff波的新观测结果来约束核幔边界的P波方位各向异性，特别关注可能的板墓地、ulvz和llvp底部区域。这些P波各向异性模型的更新描述将用于探索一些悬而未决的问题，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llvp和ulvz的性质。一系列悬而未决的问题可以通过我们新的地震观测得到更好的解决：D”层的流变学和变形机制是什么？板墓地、llvp和ulvz是如何变形的及其各向异性性质？llvp和ulvz的组成是否与D”层的其他部分不同？变形是由桥方石、后钙钛矿或次生矿物如铁方石和钙钙钛矿调节的吗？造成上地幔地震各向异性的位错蠕变是否在D”层中起作用？这些前所未有的丰富的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.