Seismological probes of Earth's outer core

外核是地球磁场的来源，也是驱动地幔对流和最终板块构造的大部分热量的来源，被认为是我们星球内部最具活力的区域。虽然地球许多其他区域的性质随深度的变化相对来说是众所周知的，但对于最上层外核的物理性质的深度变化仍然没有达成共识，特别是关于可能存在分层的轻元素富集层。这一层的存在对于理解混合良好的外核和地幔之间的热关系非常重要;这一层也可能影响地球发电机和地磁观测值。该项目将使用两种互补的地震工具，体波和低频全地球振动，调查最上层外核的特性。作为该项目的一部分，将为本科和研究生阶段的STEM学生提供教育、培训和研究经验，并为一名PI提供支持，该PI是一个在地球物理学中代表性不足的团体的成员，鼓励多样性。这个多方法项目将利用体波和地球的正常振荡模式来更好地了解最上层的外核。使用多个SmKS相位，敏感的精细速度结构，将允许在顶部外核，其中轻元素的分层层已被几个研究人员提出的压缩波速度结构的分辨率。先前的体波研究已经提出了一系列的层厚度，径向轮廓和程度的差异，从一个良好的混合外核。一些体波研究报告说，这一层的地震速度比预期的要慢，这通常被认为是外核顶部的致密物质，而不是轻质物质。通过添加来自整个地球振荡中心频率的信息，这对外核的速度和密度都很敏感，这项工作将为显然自相矛盾的最上层外核提供新的见解，而不必对存在的液体的矿物学性质做出任何假设。该项目还将使用体波观测的组合来调查任何地震学上可观察到的穿过外核切线圆柱体的区别，这是以前存在分歧的问题。该项目不仅将对我们理解这一层的地震特性产生影响，而且还将对地磁现象产生影响，如MAC和Rossby波，以检查地球的热量收支，包括地幔对流和地球发电机的动力源。它还允许将观察到的外核特性与矿物物理学的预测进行比较，以更好地了解那里存在的液态铁合金的化学成分。

The outer core, the source of Earth's magnetic field and much of the heat that powers mantle convection, and ultimately plate tectonics, is thought to be the most dynamic region of our planet's interior. While the change in properties with depth of many other regions of the Earth is relatively well known, there is still no consensus on the depth variation of physical properties in the uppermost outer core, especially with regard to the possible existence of a stratified, light element enriched layer. The presence of such a layer is important for understanding the thermal relationship between the well-mixed outer core and the mantle; the layer could also affect the geodynamo and geomagnetic observables. This project will use two complementary seismic tools, body-waves and low-frequency whole Earth vibrations, to investigate the properties of the uppermost outer core. Education, training and research experience for STEM students at the undergraduate and graduate level will be provided as part of this project as well as support for a PI who is a member of an underrepresented group in geophysics, encouraging diversity.This multi-method project will exploit both body-waves and the Earth's normal modes of oscillation to better understand the uppermost outer core. Using multiple SmKS phases, sensitive to fine velocity structure, will allow for the resolution of compressional-wave velocity structure at the top outer core, where a stratified layer of light elements has been proposed by several researchers. Previous body-wave studies have suggested a range of layer thickness, radial profiles and degree of difference from a well-mixed outer core. Some body-wave studies have reported that the layer is seismically slower than expected, which would normally be expected to correspond to dense, rather that light, material at the top of the outer core. By adding information from whole Earth oscillation center frequencies, which are sensitive to both velocity and density in the outer core, this work will provide new insights into the apparently paradoxical uppermost outer core without having to make any assumptions about the mineralogical properties of the liquid present. The project will also use a combination of body-wave observations to investigate any seismologically observable distinction across the outer core's tangent cylinder, a matter of previous disagreement. This project will have implications not only for our understanding of the seismic properties of this layer, but also for geomagnetic phenomena, such as MAC and Rossby waves, for examining the heat budget of the planet, including the power sources for mantle convection and the geodynamo. It will also permit the comparison of the observed properties of the outer core with predictions from mineral physics to better understand the chemical composition of the liquid iron alloy present there.