Refining Tomographic Models Beneath the Pacific and Margins

在绘制地球地震变化图方面取得了相当大的进展。在这次攻击中，许多不同类型的地震数据被汇集在一起，浅层结构由密集的区域阵列确定，全球结构由IRIS数据在长周期层析成像中确定。幸运的是，这些地球模型的相互比较来自不同的方法和数据集显示出一定的一致性。例如，快速下地幔环太平洋带，当检查在高频率与区域数据，显示小的三重附近的CMB指示相变和/或板屈曲。同样，模糊的层析成像图像的非洲超级羽首次在层析成像图像中识别出现作为一个独特的结构时，密集的宽带阵列在SKS旅行时间的跳跃表现出壁的锐度。不幸的是，太平洋超级羽流被太平洋包围，使其非常难以研究。此外，太平洋被俯冲带包围，全球方法无法很好地模拟这些俯冲带，起始参考模型是PREM，它有20公里的地壳和220公里处的主要上地幔不连续性;幸运的是，太平洋下的上地幔在地质历史上相对简单，很容易用一维模型解释，如果我们允许岩石圈厚度和LVZ有一些变化。TriNet数据运行堆栈的最新研究（120个台站）可以识别与上地幔反射多次波有关的第二阶段（三重）S、SS、SSS等。从这些数据产生的模型预测了各种“微屈波到达”，与多个ScS相关的上地幔反射非常好，尽管多个ScS和sScS组的相对时间显示出随位置的快速变化，至少沿着斐济-汤加到TriNet阵列。由于浅层结构的简单性，看来ScS的多次波可以为绘制与太平洋超级地幔柱尖壁相关的精细结构提供理想的数据，如果它们存在的话，并对Scd相边界提供约束，特别是沿着快速变化的边缘结构。 在这项研究中，波形建模分析应用于波形数据的优秀收集（巴哈NARS阵列，PASSCAL实验，IRIS，CISN，TriNet和新墨西哥阵列（MASE））。后者包含沿一条样带（阿卡普尔科-坦皮科）的沿着200个测站，间距约为5公里。这些努力正在产生太平洋和东部边缘下的上地幔和下地幔结构的精细图像，在410附近和沿着俯冲板发现了LVZ。更广泛的影响这个补助金支持研究生谁将获得最新的波传播技术以及反演方法的经验。我们计划开发的上地幔的详细图像也将对整个地球科学界非常有用，包括地球动力学家，地球化学家和对板块边界构造感兴趣的地质学家，特别是矿物物理学家。

Considerable progress has been made in mapping seismic variation in the Earth. Many different types of seismic data are brought together in this attack with shallow structure determined by dense regional arrays and global structure determined by using IRIS data in long-period tomographic imaging. An intercomparison of these Earth models derived from different methods and datasets fortunately show some agreement. For example, the fast lower mantle circum-Pacific belt, when examined at high-frequency with regional data, displays small triplications near the CMB indicative of phase changes and/or slab buckling. Similarly, the blurred tomographic image of the African Superplume first recognized in tomographic images appears as a distinct structure when viewed by dense broadband arrays where jumps in SKS travel times demonstrate wall sharpness. Unfortunately, the Pacific Superplume is enclosed by the Pacific Ocean making it very difficult to study. Moreover, the Pacific is surrounded by subduction zones which are not well modeled by global methods and the starting reference model is PREM which has a 20 km crust and a major upper mantle discontinuity at 220 km; neither are realistic.Fortunately, it appears that the upper mantle beneath the Pacific is relatively simple in terms of geologic history and easily explained with 1D models, if we allow some variation in the lithospheric thickness and LVZ. Recent studies of running stacks of TriNet data (120 stations) allows the identification of secondary phases associated with upper mantle reflected multiples (triplications) S, SS, SSS, etc. Models produced from this data predict the various "pegleg arrivals", upper mantle reflections associated with multiple ScS remarkably well although the relative timing of the multiple ScS and sScS groups display rapid changes with position, at least along the Fiji-Tonga to TriNet array. Because of simplicity of the shallow structure, it appears that the multiples of ScS can provide the ideal data for mapping the fine structure associated with sharp walls of the Pacific Superplume if they exist and provide constrains on the Scd phase boundary especially along the rapidly varying margin structures. In this study, waveform modeling analyses is applied to the excellent collection of waveform data (Baja NARS Array, PASSCAL experiments, IRIS, CISN, TriNet, and the new Mexican Array (MASE)). The latter contains 200 stations along a transect (Acapulco-Tampico) with roughly 5 km spacing. These efforts are producing refined images of the upper and lower mantle structure beneath the Pacific and eastern Margins where LVZs have been discovered near the 410 and along subducted slabs. Broader ImpactThis grant supports a graduate student who will gain experience in the latest wave propagation techniques as well as inversion methods. The detailed images of the upper mantle that we plan to develop will also be of great use to the entire earth science community, including geodynamicists, geochemists, and geologists interested in the tectonics of plate boundaries, and especially mineral physicists.