Global P, SV, and converted wave measurements for improved lower mantle P and S structure studies

全球 P、SV 和转换波测量，以改进下地幔 P 和 S 结构研究

• 批准号: 1853911
• 负责人: Edward Garnero
• 金额: $ 27.5万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-03-15 至 2025-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1853911&HistoricalAwards=false
• 关键词: Global; SV; converted; wave; measurements

This proposal seeks to measure every possible observable seismic wave on seismograms recorded across the globe. Measuring all possible waves involves documenting their travel times and wave shape information. These data can then be used to bolster seismic imaging efforts of Earth's mantle which currently do not routinely use multiple bouncing or echoing of waves, especially P waves. Using these waves ensures better sampling of the entire volume of the Earth's mantle. Otherwise, the southern hemisphere in particular is poorly sampled. Better imaging of Earth's mantle is important because it allows for more accurate determination of earthquake properties as well as the dynamic convection of the interior which drives plate tectonics at Earth's surface. A complete dataset of a subset of seismic waves will allow benchmarking tomographic models of different research groups, as well as permit a more direct comparison of P and S wave models of significant heterogeneities of the deep mantle. In particular, this work will study two massive low seismic wave speed structures: one beneath the Pacific Ocean, and one beneath the Atlantic Ocean and Africa. These huge structures are the largest anomalies in the planet which are unknown in nature. Resulting models will be rendered in 3D and shared with the public via the 3D Marston Theater at Arizona State University, which regularly gives science shows to the general public. The project will also support and train two students at ASU. Training the undergraduate student will involve the creation and regular updating of a data acumen training document, which will also be shared via the web. Students will be involved in data analysis, interpretation, and writing papers to be published. Scientific renderings (e.g., models and schematics) will be shared via the PI's website, as well as via direct email.This project will measure and quantify travel time behavior of a global seismic dataset of high quality P-wave phases, S-wave phases on the SV component of motion , phases having both P and SV legs in the mantle, and depth phases of P, SH, SV, and P-SV waves. The adopted approach incorporates two novel tools recently developed: (1) empirical wavelets (EWs) are constructed from the average shape of S and P waves on an event-by-event basis, which are adaptively adjusted to match variable pulse widths prevalent in data, thus minimizing travel time estimation errors; and (2) virtual stations which are built from localized geographical bin stacks of stations for phases of interest, making measurements possible for data with event-station corridors typically too low in amplitude for confident measurements. The new seismic measurements proposed here will document travel times along with several attributes of all measured waveforms, including wave shape information (amplitude, waveform broadness, waveform misfit compared to the best fitting EW), signal-to-noise ratios (SNRs, measured multiple ways), and cross-correlation coefficients (CCCs, between phases of interest and best-fitting EWs). The investigators will measure minor and major arc data at relatively short periods (10-16 sec). The new datasets aim to improve resolution in P and S seismic imaging of the Earth's mantle, with the goal of improving understanding of the structure, dynamics, and evolution of the Earth. These data will improve wave path coverage in the southern hemisphere, be applicable to imaging studies of the entire mantle, and be made publicly available along with a recently completed SH dataset using the same methodology. The data will be used for imaging large-low velocity provinces, with a focus on comparing P and S velocity heterogeneity, which bears upon the nature of heterogeneity. This work will fund a PhD student and an undergraduate student to collect, process, measure, and review P and SV seismic data. The PI will mentor the students within a broader perspective of the multidisciplinary nature of mantle heterogeneity, particularly the dynamics and evolution of the mantle, with participation in ASU's multidisciplinary geophysics group (seismology, mineral physics, geodynamics, and planetary geophysics). All data measurements, models, and codes will be openly shared with the community via the web, as well as IRIS's tomography model portal. All measurements will be shared with the 3D Reference Earth Model project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

这项提议寻求测量全球记录的地震图上的每一种可能的可观测地震波。测量所有可能的波浪包括记录它们的旅行时间和波形信息。然后，这些数据可以用来支持地幔的地震成像工作，目前地幔通常不使用多次波的反弹或回波，特别是P波。使用这些波可以确保对整个地幔体积进行更好的采样。否则，南半球的采样尤其糟糕。更好的地幔成像很重要，因为它可以更准确地确定地震性质，以及驱动地球表面板块构造的内部动态对流。地震波子集的完整数据集将允许对不同研究小组的层析模型进行基准比较，并允许更直接地比较具有显著非均质性的深部地幔的P波和S波模型。特别是，这项工作将研究两个巨大的低地震波速结构：一个在太平洋下面，一个在大西洋和非洲下面。这些巨大的结构是地球上最大的异常现象，在自然界中是未知的。生成的模型将以3D形式渲染，并通过亚利桑那州立大学的3D马斯顿剧院与公众分享，该剧院定期向普通公众提供科学表演。该项目还将支持和培训亚利桑那州立大学的两名学生。对本科生的培训将包括创建和定期更新数据敏锐性培训文档，该文档也将通过网络共享。学生将参与数据分析、解释和撰写即将发表的论文。科学效果图(如模型和示意图)将通过PI的网站和直接电子邮件共享。该项目将测量和量化高质量P波震相、SV运动分量上的S波震相、地幔中同时具有P和SV腿的震相以及P、SH、SV和P-SV波的深度震相的全球地震数据集的旅行时间行为。所采用的方法结合了最近开发的两个新工具：(1)经验小波(EW)是由逐个事件的S波和P波的平均形状构造的，它可以进行自适应调整，以匹配数据中普遍存在的可变脉冲宽度，从而将旅行时间估计误差降至最低；(2)虚拟台站，它是由感兴趣相位的局部地理面元堆叠构建的，使得对于振幅通常太低的事件-台站走廊数据的测量成为可能。这里提出的新的地震测量将记录走时以及所有测量波形的几个属性，包括波形信息(与最佳拟合EW相比的幅度、波形宽度、波形不匹配)、信噪比(SNR，多路测量)和互相关系数(CCCS，感兴趣的相位和最佳拟合EW之间的CCCS)。调查人员将以相对较短的周期(10-16秒)测量小弧度和大弧度数据。新的数据集旨在提高P和S对地幔的地震成像的分辨率，目的是提高对地球结构、动力学和演化的理解。这些数据将改善南半球的波路覆盖，适用于整个地幔的成像研究，并将与最近完成的SH数据集一起使用相同的方法公开。这些资料将用于大-低速区的成像，重点比较P波和S速度的非均质性，这与非均质性的性质有关。这项工作将资助一名博士生和一名本科生收集、处理、测量和审查P和SV地震数据。PI将指导学生在更广泛的角度了解地幔不均质性的多学科性质，特别是地幔的动力学和演化，并参与亚利桑那州立大学的多学科地球物理小组(地震学、矿物物理、地球动力学和行星地球物理)。所有数据测量、模型和代码将通过网络和IRIS的断层扫描模型门户与社区公开共享。所有测量结果将与3D参考地球模型项目共享。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。