Characterizing Radial Heterogeneity in the Mid Mantle

尽管在过去的十年里地球化学、地球动力学和地震成像方面取得了重大进展，但地球地幔的化学分区仍然是个谜。 它对地幔动力学的重要性是很难夸大的，破译它，即使是部分，无疑将提高我们对地球化学演化和动力学的理解。 在这一建议中，PI概述了一个研究方案，以表征中地幔（即深度约1000和2500公里之间）的地震速度不均匀性。 他将采取三种互补的办法。 第一个扩展ScS混响映射，以科普强烈变化的沿路径结构。 这项工作将提供中地幔剪切波阻抗变化的限制，并可以应用到与现今俯冲作用的相互作用很小的路径。 这一点很重要，因为大多数中地幔散射不均匀性的地震成像都是俯冲带，呈现出潜在的过渡带结构的倾斜视图。第二种方法使用小型和区域地震（100公里孔径）阵列记录的高频体波。 S-to-P转换，前向散射P，和P-to-S前体S将使用源阵列在汤加斐济，阿留申群岛和南美洲和中美洲进行调查。与大多数先前的工作不同，这将广泛地研究慢度-时间空间的P-PcP和S-ScP线，调查中地幔反向散射P波的证据。第三种方法是调整双阵列的叠加方法，将这种以能量为中心的方法与PI为检查区域阵列下的地壳结构而开发的统计迁移方法相结合。 通过使用对短尺度结构敏感性强且局部化的相位来广泛表征中地幔的不均匀性，PI希望看到速度层析成像所不能看到的：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。这一提议将为博士学位提供资金。研究工作的一名研究生，并聘请了几名本科生进行初步的数据分析。拟开发的方法旨在最大限度地提高EarthScope等大型不规则阵列的能力，并可能用于其他领域，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.