Exploring Anisotropy in the Deep Earth

地球上大部分地区的地震波传播是各向异性的，地震波以不同的速度在不同的方向传播。各向异性存在于地壳、上地幔，特别是俯冲带、下地幔主要是最底带和内核中。产生导致地球深处各向异性的晶体排列的详细机制仍然知之甚少。该项目将进行高压和高温的实验和建模，通过定量分析在地球深部条件下形成的晶体的首选取向模式来探索这一过程。该项目将提供解释宏观地震观测的关键数据。但是，同步加速器衍射的方法，以及先进的数据分析方法，也与广泛的物理科学相关。所开发的实验和建模方法将提供给其他研究人员。将通过出版物、讲习班、培训和分发软件来促进它们。这项研究将资助一名博士生的研究。该项目的主要目标是促进对地球动力学对流活动机制的理解。塑性变形很大程度上归因于位错蠕变，但其他机制可能起重要作用，特别是动态再结晶。本项目将探索新的方法，如同步多晶晶体学，以研究下地幔条件下的成核和晶粒生长。这些下地幔矿物的实验结果，如环woodite， bridgmanite， ferropericlase和后钙钛矿，将用于模拟对流下地幔的各向异性。与以往依赖位错滑动的模型相反，这项工作将包括再结晶，并研究优选晶体排列对动态流动的影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Large regions of the Earth are anisotropic for propagation of seismic waves, which are waves that propagate at different speeds in different directions. Anisotropy is present in the crust, in the upper mantle, particularly subduction zones, in the lower mantle mainly the lowermost zone, and the inner core. The detailed mechanisms that produce the crystal alignments that lead to anisotropy in the deep Earth are still poorly understood. This project will conduct experiments and modeling of high pressure and temperature to explore the processes by quantitative analysis of preferred orientation patterns of crystals that form at deep Earth conditions. The project will provide data that are critical for interpreting macroscopic seismic observations. But the methods in synchrotron diffraction that will be developed, as well as advanced methods of data analysis, are also relevant for a broad range of physical sciences. The experimental as well as modeling methodologies that are developed will be made available to other researchers. They will be promoted through publications, workshops, training and distribution of software. The research will fund the research of a PhD student.The primary goal of this project is to advance understanding of mechanisms that are active during geodynamic convection. Plastic deformation has been largely attributed to dislocation creep but other mechanisms are likely to play an important role, particularly dynamic recrystallization. This project will explore new methods such as synchrotron multigrain crystallography to study nucleation and grain growth in situ at lower mantle conditions. The outcomes of these experiments on lower mantle minerals such as ringwoodite, bridgmanite, ferropericlase and postperovskite will be used to model anisotropy in a convective lower mantle. Contrary to previous models that relied on dislocation glide, this work will include recrystallization and also investigate the influence of preferred crystal alignment on dynamic flow.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.