Refining Tomographic Models Beneath the Pacific and Margins

在绘制地球上的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汇聚在一起，其中浅层结构由密集的区域阵列确定，而全球结构则由长周期层析成像中的IRIS数据确定。幸运的是，对来自不同方法和数据集的这些地球模型的相互比较显示出一些一致之处。例如，快速的下地幔环太平洋带，当用区域数据进行高频检查时，在CMB附近显示出指示相变和/或板条屈曲的小三重。同样，首先在断层图像中识别出的非洲超烟羽的模糊断层图像，当通过密集的宽带阵列观察时，看起来是一个明显的结构，SKS旅行时间的跳跃显示了墙壁的清晰度。不幸的是，太平洋超级羽流被太平洋包围，这给研究带来了很大的困难。此外，太平洋被俯冲带包围，这些俯冲带没有被全球方法很好地模拟，初始参考模型是PREM，它有20公里的地壳和220公里处的主要上地幔不连续；两者都不现实。幸运的是，太平洋下面的上地幔在地质历史方面似乎相对简单，很容易用一维模型来解释，如果我们允许岩石圈厚度和低层厚度的一些变化的话。最近对TriNet数据(120个台站)运行叠加的研究可以识别与上地幔反射多次(三次)S、SS、SSS等有关的次生相。根据这些数据产生的模型可以很好地预测与多个SCS有关的各种“钉腿到达”、上地幔反射，尽管多个SCS和SSCS组的相对时间显示出随位置的快速变化，至少沿斐济-汤加到Trinet阵列是这样。由于浅层结构的简单性，SCS的多次波似乎可以为绘制与太平洋超强羽流尖壁相关的精细结构提供理想的数据，并对SCD相边界提供约束，特别是沿快速变化的边缘结构。在这项研究中，波形建模分析被应用于优秀的波形数据收集(Baja NARS阵列、PASSCAL实验、IRIS、CISN、TriNet和新的墨西哥阵列(MASE))。后者包括沿一条样带(阿卡普尔科-坦皮科)的200个测站，间隔约5公里。这些努力正在制作太平洋和东部边缘之下的上、下地幔结构的精细图像，在410附近和俯冲板块附近发现了低空区域。更广泛的影响这笔助学金支持一名研究生，他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.