The viscosity structure of Earth's mantle, even the 1‐D radial viscosity profile, remains not well constrained. The dynamics of the subducting slabs is strongly affected by, and can be used to constrain, the viscosity structure of the mantle. Here, we perform fully dynamic, self‐consistent mantle convection models to study the dynamics of subducted slabs in the deep mantle. We use a statistical analysis approach to quantify how the depth distribution of flat‐lying slabs is affected by the depth‐dependence of mantle viscosity. We find that, for cases in which the viscosity increases at 660 km depth, whether sharply or gradually, flat‐lying slabs preferentially occur above this depth, and importantly, up to ∼30% of the subducted slabs previously flatted at this depth later sink to the deep lower mantle and maintain a flat‐lying morphology. The frequency of (or the probability to have) flat‐lying slabs at ∼1,000 km depth in these cases is similar to cases in which the viscosity jump occurs at 1,000 km depth. Therefore, to explain the presence of flat‐lying slabs at ∼1,000 km depth for the Earth does not require a viscosity jump at this depth. In contrast, a viscosity jump merely occurring at ∼1,000 km depth causes a lack of flat‐lying slabs in the uppermost lower mantle at ∼700–900 km depth and is inconsistent with seismic observations. The presence of flat‐lying slab materials in the Earth's uppermost lower mantle requires a viscosity increase at 660 km depth.

中文翻译：

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从平板停滞事件的统计分析约束地幔粘度结构

地球地幔的粘度结构，甚至是一维径向粘度分布图，都没有得到很好的约束。俯冲板的动力学受到地幔粘度结构的强烈影响，并可以用来约束地幔的粘度结构。在这里，我们执行完全动态的，自洽的地幔对流模型，以研究深地幔中俯冲板的动力学。我们使用统计分析方法来量化平坦平板的深度分布如何受到地幔粘度的深度依赖性的影响。我们发现，对于粘度在660 km深度处急剧增加或逐渐增加的情况，平坦平板优先出现在该深度以上，重要的是，之前在该深度平坦的俯冲平板中，最多约有30％后来沉没下地幔深处并保持平坦的形态。在这种情况下，在约1,000 km深度处平坦平板的频率（或出现概率）类似于在1000 km深度处发生粘度跳跃的情况。因此，要解释地球上约1,000 km深度处存在平坦平板，就不需要在该深度出现粘度跳跃。相反，仅在约1000 km深度处发生粘度跃变，导致在约700-900 km深度的最下部下地幔中缺乏平坦平板，这与地震观测结果不一致。在地球最下部的地幔中存在平坦的平板材料时，需要在660 km深度处增加粘度。为解释地球在约1,000 km深度处存在平坦平板，不需要在该深度下发生粘度跳跃。相反，仅在约1000 km深度处发生粘度跃变，导致在约700-900 km深度的最下部下地幔中缺乏平坦平板，这与地震观测结果不一致。在地球最下部的地幔中存在平坦的平板材料时，需要在660 km深度处增加粘度。为解释地球在约1,000 km深度处存在平坦平板，不需要在该深度下发生粘度跳跃。相反，仅在约1000 km深度处发生粘度跃变，导致在约700-900 km深度的最下部下地幔中缺乏平坦平板，这与地震观测结果不一致。在地球最下部的地幔中存在平坦的平板材料时，需要在660 km深度处增加粘度。