Outer-core compositional stratification from observed core wave speed profiles
Outer-core compositional stratification from observed core wave speed profiles
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DOI：
10.1038/nature09636
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发表时间：
2010-12-09
期刊：
影响因子：
64.8
通讯作者：
Kaneshima, Satoshi
中科院分区：
文献类型：
--
作者：
Helffrich, George;Kaneshima, Satoshi
轻元素必须存在于接近纯铁的地球核心中，以匹配远程观测到的外核和内核的特性（1,2）。内核的结晶将固体中的轻元素排除在外，将它们集中在靠近内核边界的液体中，这些液体可能上升并聚集在内核的顶部(3)，这可能具有可观测到的地震信号。在这里，我们提出了基于阵列的对这部分核心敏感的地震波观测，其波速要求在外核最上面300公里处存在径向成分变化。速度分布与均质液体压缩时的速度分布明显不同。如果在Fe-O-S系统中模拟，在核心顶部的总轻元素富集可达5%的重量。分层表明在外核的顶部存在一个次绝热的温度梯度。
Light elements must be present in the nearly pure iron core of the Earth to match the remotely observed properties of the outer and inner cores(1,2). Crystallization of the inner core excludes light elements from the solid, concentrating them in liquid near the inner-core boundary that potentially rises and collects at the top of the core(3), and this may have a seismically observable signal. Here we present array-based observations of seismic waves sensitive to this part of the core whose wave speeds require there to be radial compositional variation in the topmost 300 km of the outer core. The velocity profile significantly departs from that of compression of a homogeneous liquid. Total light-element enrichment is up to five weight per cent at the top of the core if modelled in the Fe-O-S system. The stratification suggests the existence of a subadiabatic temperature gradient at the top of the outer core.