Characterizing Radial Heterogeneity in the Mid Mantle

尽管地球化学、地球动力学和地震成像在过去十年中取得了重大进展，但地幔的化学划分仍然是一个谜。它对地幔动力学的重要性怎么强调都不为过，破译它，即使是部分破译，无疑会提高我们对地球化学演化和动力学的理解。在该提案中，PI概述了一个研究方案，以表征中地幔（即~1000至2500 km深度之间）的地震速度非均质性。他将采取三种互补的方法。第一个扩展了sc混响映射，以应对强烈变化的沿路径结构。这项工作将提供对中地幔横波阻抗变异性的限制，并可应用于与现今俯冲作用很少相互作用的路径。这一点很重要，因为大多数中地幔散射非均质性的地震成像都是俯冲带的，这可能会对次过渡带的结构产生偏差。第二种方法使用小型和区域地震（孔径100公里）阵列记录高频体波。将利用汤加-斐济、阿留申群岛和中南美洲的源阵列调查S-to-P转换、前向散射P和P-to-S前体S。与大多数先前的工作不同，这将广泛地研究慢速-时间-空间的P- pcp和S-ScP线，调查中地幔中反向散射P波的证据。第三种方法是调整包络叠加方法用于双阵列，将这种以能量为中心的方法与PI开发的用于检查区域阵列下地壳结构的统计迁移方法相结合。通过使用对短尺度结构敏感且局部化的相广泛表征中地幔非均质性，PI希望看到速度层析成像无法看到的东西：化学分层和/或地幔“斑点”的证据。“更广泛的影响：PI将传播结果，提供目前尚未公开存档的数据集，通过IRIS发布所有新算法的代码，并在PI的网页上以原始和图形形式呈现数值结果。该提案将资助一名研究生的博士研究工作，并将雇用几名本科生进行初步数据分析。正在开发的方法旨在最大限度地提高像EarthScope这样的大型不规则阵列的能力，并可能在其他领域得到应用，例如远程声纳阵列探测。

RevenaughThe chemical partitioning of the Earth's mantle remains enigmatic despite significant advancements in geochemistry, geodynamics and seismic imaging in the past decade. Its importance to mantle dynamics is hard to overstate, and deciphering it, even in part, would undoubtedly improve our understanding of the chemical evolution and dynamics of our planet. In this proposal, the PI outlines a program of study to characterize the seismic velocity heterogeneity in the mid-mantle (i.e, between depths of ~1000 and 2500 km). He will pursue three complimentary approaches. The first extends ScS reverberation mapping to cope with strongly varying along-path structure. This work will offer constraints on mid-mantle shear-wave impedance variability and can be applied to paths with little interaction with present-day subduction. This is important inasmuch as most seismic imaging of mid-mantle scattering heterogeneity is of subduction zones, presenting a potentially skewed view of sub-transition zone structure. The second approach uses small and regional seismic 100 km aperture) array recordings of high-frequency body waves. S-to-P conversions, forward-scattered P, and P-to-S precursors to S will be investigated using source arrays in Tonga-Fiji, the Aleutians and South and Central America. Unlike most prior work, this will look extensively at the P-PcP and S-ScP lines of slowness-time space, investigating evidence of back-scattered P waves in the mid-mantle. The third approach is to adapt envelope-stacking methods for use with dual-arrays, combining this energy-centric approach with the statistical migration methods the PI has developed for examining crustal structure beneath regional arrays. By extensively characterizing mid-mantle heterogeneity using phases whose sensitivity to short-scale structure is strong and localized, the PI hopes to see what velocity tomography can't: evidence of chemical layering and/or mantle "blobs."Broader impacts: The PI will disseminate the results, making available data sets that are not publicly archived at present, publishing codes of all new algorithms through IRIS, and presenting numerical results in raw and graphical form on the PI's webpages. This proposal would fund the Ph.D. research work for one graduate student and would employ several undergraduates for preliminary data analysis. The methods to be developed are intended to maximize the capabilities of large, irregular arrays like EarthScope and may have use in other fields, such as long-range sonar array sounding.