The dynamics of Earth's D″ layer at the base of the mantle plays an essential role in Earth's thermal and chemical evolution. Mantle convection in D″ is thought to result in seismic anisotropy; therefore, observations of anisotropy may be used to infer lowermost mantle flow. However, the connections between mantle flow and seismic anisotropy in D″ remain ambiguous. Here, we calculate the present-day mantle flow field in D″ using 3D global geodynamic models. We then compute strain, a measure of deformation, outside the two large-low velocity provinces (LLVPs) and compare the distribution of strain with previous observations of anisotropy. We find that, on a global scale, D″ materials are advected toward the LLVPs. The strains of D″ materials generally increase with time along their paths toward the LLVPs and toward deeper depths, but regions far from LLVPs may develop relative high strain as well. Materials in D″ outside the LLVPs mostly undergo lateral stretching, with the stretching direction often aligning with mantle flow direction, especially in fast flow regions. In most models, the depth-averaged strain in D″ is >0.5 outside the LLVPs, consistent with widespread observations of seismic anisotropy. Flow directions inferred from anisotropy observations often (but not always) align with predictions from geodynamic modeling calculations.

中文翻译：

---

地球最深地幔中的流动和变形：地球动力学建模的见解以及与地震观测的比较


地幔底部的地球 D“ 层的动力学在地球的热演化和化学演化中起着至关重要的作用。D“ 中的地幔对流被认为会导致地震各向异性;因此，各向异性的观测可用于推断最底层的地幔流。然而，D“ 中地幔流和地震各向异性之间的联系仍然不明确。在这里，我们使用三维全球地球动力学模型计算了当今 D“ 中的地幔流场。然后，我们计算了两个大低速省 （LLVP） 之外的应变（一种变形量度），并将应变分布与之前观察到的各向异性进行比较。我们发现，在全球范围内，D“ 材料向 LLVP 平流。D“ 材料的应变通常随着时间的推移而增加，沿着它们朝向 LLVPs 和更深的深度移动，但远离 LLVPs 的区域也可能产生相对较高的应变。LLVP 外 D“ 中的材料大多发生横向拉伸，拉伸方向通常与地幔流向一致，尤其是在快速流动区域。在大多数模型中，D“ 中的深度平均应变在 LLVP 之外为 >0.5，这与地震各向异性的广泛观测一致。从各向异性观测中推断的流向通常（但并非总是）与地球动力学建模计算的预测一致。