Collaborative Research: Mantle dynamics and plate tectonics constrained by converted and reflected seismic wave imaging beneath hotspots

合作研究：热点下方转换和反射地震波成像约束的地幔动力学和板块构造

• 批准号: 2147923
• 负责人: Peter Shearer
• 金额: $ 21.45万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-02-01 至 2025-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2147923&HistoricalAwards=false
• 关键词: Collaborative; Research; Mantle; dynamics; plate

Since its formation billions of years ago, Earth has been slowly cooling via convection, where warmer material rises to the surface and cold tectonic plates plunge deep into the interior. Understanding this process is important for a wide range of problems, such as determining the factors that drive plate tectonics to sustaining deep water and carbon cycles that stabilize the atmosphere/hydrosphere and climate throughout Earth history. This is particularly relevant for society, both because plate tectonic processes are the driving forces behind hazards such as earthquakes and volcanoes and also because our climate and atmosphere make Earth habitable. This project studies large scale convection in the solid Earth by using earthquake data recorded at distant seismic stations in regions of upwelling. Upwellings are notoriously difficult to constrain. The focus will be on three end-member cases: 1) Hawaii, the classic example where deep upwelling occurs beneath ocean lithosphere, 2) Yellowstone, the classic example of deep upwelling that occurs beneath a continent, and 3) the equatorial mid-Atlantic Ridge, which is typically assumed to be a location without deep upwellings. The project will use classic techniques and also some newly developed approaches to better constrain the scale of the upwellings and their pathways. An outreach program will increase diversity in the Earth Sciences via public engagement and education and training of students and early career researchers. The outreach portion includes visits to core discipline classrooms at Morgan State University, a historically black university, with an established connection with two faculty members there. The goal of the visits and the materials is to increase awareness of career possibilities and also the societal relevance of the Earth Sciences. The approach is modeled on the success of the "Google in Residence" program that successfully placed Google engineers on HBCU campuses. Eventually a wider range of Earth scientists will be included by developing an archive of materials that can be scaled and adapted according to needs and also best-practice advice, both of which will be made publicly available to the broader scientific community. The project also provides training for undergraduate students, a graduate student, and a post doc in cutting-edge methodologies and use of seafloor seismic data. Earth’s convective system is important for understanding the evolution of the planet, including everything from the factors that drive and enable plate tectonics to sustaining deep water and carbon cycles that stabilize the atmosphere/hydrosphere and climate over billions of years. It is generally accepted that cool mantle sinks back into the Earth, e.g., at subduction zones, and hot mantle rises, e.g., beneath hotspots and mid ocean ridges. Although mantle tomography has resolved many seismically fast anomalies associated with subduction, imaging upwellings has proven more challenging, potentially because seismic waveforms have difficulty resolving thin slow conduits. Thus, the exact dimensions, locations, characteristics, origin depths and magnitudes of these thermal anomalies are poorly known, as well as their chemical and physical interaction with the surrounding mantle, such as in the transition zone and uppermost mantle. Similarly, the degree to which upwellings change in size and/or are deflected during their ascent and how they vary among tectonic environments is uncertain. Converted and reflected wave imaging of the transition zone discontinuities and the lithosphere-asthenosphere boundary should provide tighter constraints. However, there are some discrepancies in studies using these methods regarding hotspot character and location, perhaps because they have used different methodologies and approaches with different sensitivities in different locations. This study will examine this issue systematically at a varied suite of tectonic environments. The planned approach will use the complementary sensitives of converted and reflected seismic phases to image the lithosphere-asthenosphere boundary and transition zone discontinuities beneath three key regions that are representative of the range of tectonic environments where variability in upwelling characteristics might be expected. These include the iconic hotspot of Hawaii near the center of an old oceanic plate, the classic example of Yellowstone hotspot beneath a continental interior, and finally the mid-Atlantic Ridge where deep upwellings are not predicted by classic models. Analyses will include P-to-S imaging of the transition zone discontinuities and S-to-P imaging of the lithosphere-asthenosphere boundary, both sensitive to vertical changes in shear wave velocity, and also use S-reflections, which have the added advantage of high depth resolution. A systematic approach will allow comparisons among the regions and anisotropic testing and F-K full-waveform modelling will be performed to determine the influence of anisotropy and/or focussing/defocussing for any apparent discrepancies. Once a full range of possibilities is defined from the seismic waveforms, inversions for Earth properties based on experimental and ab initio constraints will determine the properties that can explain the observations.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.

自数十亿年前形成以来，地球一直通过对流缓慢冷却，其中较温暖的物质上升到表面，而冷的构造板块深入内部，了​​解这一过程对于许多问题都很重要，例如确定影响因素。推动板块构造维持深水和碳循环，从而稳定整个地球历史中的大气/水圈和气候，这对于社会尤其重要，因为板块构造过程是地震和火山等灾害背后的驱动力。因为我们的气候和大气使地球适合居住。该项目通过使用在上升流区域的遥远地震站记录的地震数据来研究固体地球中的大规模对流，重点是三个端元情况。 ：1) 夏威夷，海洋岩石圈下方发生深层上升流的经典例子，2) 黄石公园，大陆下方发生深层上升流的经典例子，3) 赤道大西洋中脊，该项目通常被认为是没有深层上升流的位置，该项目将使用经典技术和一些新开发的方法来更好地限制上升流的规模及其路径。外展部分包括参观摩根州立大学的核心学科教室，这是一所历史悠久的黑人大学，与那里的两名教职人员建立了联系。访问和材料的目的是提高认识。职业可能性以及地球的社会相关性该方法以“Google in Residence”计划的成功为蓝本，该计划成功地将 Google 工程师安置在 HBCU 校园中，最终将通过开发可扩展和适应的材料档案来纳入更广泛的地球科学家。需求和最佳实践建议，这两者都将向更广泛的科学界公开提供，该项目还为本科生、研究生和博士后提供有关海底地震数据的前沿方法和使用的培训。 .地球的对流系统对于理解地球的演化非常重要，包括从驱动和促成板块构造的因素到维持数十亿年来稳定大气/水圈和气候的深水和碳循环的一切。人们普遍认为，凉爽的地幔。尽管地幔断层扫描已经解决了许多与地震相关的快速异常，但地幔会沉入地球，例如在俯冲带，而热地幔会上升，例如在热点和大洋中脊下方。俯冲、上升流成像已被证明更具挑战性，可能是因为地震波形难以解析薄慢管道，因此，这些热异常的确切尺寸、位置、特征、起源深度和强度以及它们的化学和物理相互作用知之甚少。与周围的地幔（例如过渡带和上地幔）类似，上升流在上升过程中的大小变化和/或偏转程度以及它们在构造环境中的变化方式是不同的。过渡带不连续性和岩石圈-软流圈边界的转换波和反射波成像应该提供更严格的约束，但是，使用这些方法对热点特征和位置进行的研究存在一些差异，这可能是因为它们使用了不同的方法和方法。这项研究将在不同的构造环境中系统地研究这个问题，计划的方法将使用转换和反射地震相位的互补敏感性来成像。三个关键区域下方的岩石圈-软流圈边界和过渡带不连续性代表了可能出现上升流特征变化的构造环境范围，其中包括夏威夷靠近旧海洋板块中心的标志性热点，这是典型的例子。大陆内部下方的黄石热点，最后是大西洋中脊，经典模型无法预测深层上升流，分析将包括过渡带的 P-S 成像。岩石圈-软流圈边界的不连续性和 S-to-P 成像，都对剪切波速度的垂直变化敏感，并且还使用 S 反射，这具有高深度分辨率的额外优势。一旦定义了全部可能性，将进行区域和各向异性测试以及 F-K 全波​​形建模，以确定各向异性和/或聚焦/散焦对任何明显差异的影响。基于实验和从头算约束的地球特性的地震波形、反演将反映可以解释观测结果的特性。该奖项是 NSF 的法定使命，并且通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。