The physical nature of two regions called large low-shear-velocity provinces at the base of Earth's mantle is uncertain. A measurement of their density has implications for our understanding of mantle dynamics. See Article p.321 The interior composition of Earth can be estimated by imaging seismic waves changing speed as they travel through different materials, but some anomalies in the deep mantle remain challenging to explain. Fast wave speed anomalies appear in areas with a history of subduction, indicating relatively cold and dense mantle material driving downward flow. However, slow wave speed anomalies in the form of large domes above the core–mantle boundary remain contentious—in particular their net buoyancy. Harriet Lau and co-authors estimate Earth's deep mantle buoyancy using GPS-based measurements of the daily deformation of Earth in response to the gravitational pull of the Sun and the Moon. They show that the mean excess density across the bottom two-thirds of these lower-mantle domes is about 0.5 per cent. The authors conclude that these structures are enriched with high-density chemical components, probably originating from subducted oceanic plates or primordial material associated with Earth's formation.

中文翻译：

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地球物理学：地球深部地幔的浮力

地幔底部被称为大型低剪切速度区的两个区域的物理性质尚不确定。测量它们的密度对我们理解地幔动力学具有重要意义。参见文章第 321 页 可以通过对地震波在穿过不同材料时改变速度的成像来估计地球的内部成分，但深部地幔中的一些异常现象仍然难以解释。快速波速异常出现在有俯冲历史的地区，表明相对寒冷和致密的地幔物质推动了向下流动。然而，核心-地幔边界上方的大圆顶形式的慢波速度异常仍然存在争议，特别是它们的净浮力。Harriet Lau 和合著者估计地球' 深地幔浮力使用基于 GPS 的地球日常变形测量，以响应太阳和月球的引力。他们表明，这些下地幔圆顶底部三分之二的平均过剩密度约为 0.5%。作者得出结论，这些结构富含高密度化学成分，可能源自俯冲的海洋板块或与地球形成相关的原始物质。