Mantle Composition and Dynamics as Inferred from the Structure of the Upper Mantle Discontinuities

名义深度为410 km和660 km的上地幔不连续面划定了地幔过渡带的上下界，为构建地球的热模型和成分模型提供了重要的约束条件。随着地震处理技术和数据密度的提高，不连续结构图像显示出更多的非均质结构。这些不均匀性包括深度、清晰度和跨越不连续的阻抗对比的变化，距离仅为100公里。这种变化需要修正地幔成分模型和我们对不连续深度的因素的理解。该项目旨在根据USArray的初始数据确定上地幔不连续体的深度和结构，并开发技术来研究过渡带深度可能存在的各向异性程度。这项工作的科学目标将通过对地幔结构进行系统的调查来实现，以便通过估计上地幔不连续的清晰度和评估不连续清晰度的变异性来为未来的地幔模型提供地震框架。此外，将研究地幔地震性质的方位依赖性，以确定它是否可能是由于上地幔底部或过渡带的各向异性造成的。然后，这些观测结果将与矿物物理实验的约束相结合，并与之进行比较，以改进地幔成分和水含量的模型。

0454558GilbertThe upper mantle discontinuities at the nominal depths of 410 and 660 km demarcate the upper and lower bounds of the mantle transitions zone and provide important constraints for constructing thermal and compositional models of the Earth. As seismic processing techniques and data density have improved, images of discontinuity structure have revealed more heterogeneous structure. These heterogeneities include variations in the depth, sharpness, and impedance contrast across the discontinuities over distances of just a few 100 km. Such variations require a revision of mantle compositional models and our understanding of factors responsible for discontinuity depths. This project is aimed at determining the depths and structure of the upper mantle discontinuities from the initial USArray data and developing techniques to study the degree to which anisotropy may be present at transition zone depths. The scientific goals of this work will be achieved by undertaking a systematic investigation into mantle structure in order to provide a seismic framework for future mantle models by estimating the sharpness of the upper mantle discontinuities and assessing the variability of discontinuity sharpness. Additionally, the azimuthal dependence of seismic properties in the mantle will be investigated in order to determine whether it can be due to anisotropy at the base of the upper mantle or transition zone. These observations will then be integrated with, and compared to, constraints from mineral physics experiments in order to improve models of mantle composition, and water content.