Characterizing Radial Heterogeneity in the Mid Mantle

尽管在过去的十年里，在地球化学、地球动力学和地震成像方面取得了重大进展，但地幔的化学分配仍然是个谜。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。在这项建议中，PI概述了一项研究计划，以表征中地幔(即深度约1000至2500公里之间)的地震速度不均匀。他将采取三种相辅相成的方式。第一种方法扩展了SCS混响映射，以适应强变化的沿途结构。这项工作将对地幔中横波波阻抗变异性提供约束，并可应用于与现代俯冲作用很小的路径。这一点很重要，因为大多数中地幔散射不均匀的地震成像都是俯冲带的，呈现出对次过渡带结构的潜在倾斜的看法。第二种方法使用高频体波的小型和区域性地震(100千米口径)阵列记录。将利用汤加-斐济、阿留申群岛和中南美洲的震源阵列研究S到P的转换、正向散射P和P到S的前兆。与大多数以前的工作不同，这项工作将广泛地研究P-PCP和S-SCP慢度-时间空间的线，调查中地幔中P波反向散射的证据。第三种办法是使包络叠加方法适用于双阵列，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偏移方法结合起来。通过使用对短尺度结构敏感的相广泛地表征地幔中的非均质性，PI希望看到速度断层成像所不能看到的：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。这项提议将为一名研究生的博士研究工作提供资金，并将雇用几名本科生进行初步数据分析。将要开发的方法旨在最大限度地发挥像EarthScope这样的大型不规则阵列的能力，并可能在其他领域使用，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.