Collaborative Research: Mapping and Understanding Seismic Anisotropy in the Northeast Pacific Ocean

合作研究：绘制和了解东北太平洋地震各向异性

• 批准号: 1830991
• 负责人: John Collins
• 金额: $ 17.88万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-01-15 至 2024-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1830991&HistoricalAwards=false
• 关键词: Collaborative; Research; Mapping; Understanding; Seismic

Understanding the structure of the seafloor and how plate tectonics, which causes plate motion, volcanism, and megathrust earthquakes in subduction zones works, is important for understanding various types of geohazards and what triggers them. This knowledge is critical in order to plan for and understand how to mitigate and/or minimize the impact of disasters, such as those that have occurred in recent years in Thailand and Japan. Global seismic tomography, which uses seismic signals from earthquakes and other earth movements to image Earth's deep structure, has long been the tool of choice to image and understand the structure of Earth's interior and how it deforms. To this end, present tomographic images indicate that the northeast Pacific plate in the area between the continental U.S. and Hawaii is more complex than predicted by present oceanic plate models. Because this apparently atypical area is far from any type of known thermal feature, such as a mid-ocean ridge or a hotspot (i.e., a concentrated upwelling of heat and thus magma from deep inside the Earth like that which formed the Hawaiian Islands) a different mechanism must be acting. Due to the current lack of seismic recording stations in the northeast Pacific, the resolution of crustal and underlying mantle structure in this area is under-resolved and may have resulted in misleading theories of how the Pacific plate has evolved over time. This research addresses this problem by deploying an array of 25 ocean bottom seismometers for 15 months to capture and record seismic signals from earth motions. These data will allow the determination of real structures and will target the part of the Pacific plate that is 40-50 million years old. These new seismic data will allow exploration of the local seismic anisotropy (the nonuniform mineral/crustal structural orientation). Anisotropy forms when mantle minerals align with mantle flow directions or when a plate, such as the Pacific plate, responds to forces tugging along its edges. The analysis of seismic anisotropy therefore allows scientists to explore mantle processes that form, move, and ultimately cause the subduction of Earth's tectonic plates. Broader impacts of the project include graduate student and postdoctoral training in state-of-the-art geophysical at-sea and onshore seismic processing and modeling. Undergraduate students will be involved with special projects. The work complements other international global seismology efforts and involves collaboration with U.K., German, and French scientists. The work broadens participation of underrepresented groups in the sciences by supporting two investigators whose gender is underrepresented in the sciences and who serve as role models for students and other geoscientists.This research provides an integrated analyses of seismic and other geophysical data that will elucidate the structure, heterogeneity, and dynamics of the ocean crust, lithosphere and asthenosphere in a 600~kilometer wide region west of the Moonless Mountain Seamounts on the Pacific plate halfway between the US mainland and Hawaii. Seismic data will be collected using an array of 25 ocean bottom seismometers. Research targets include a regional study, covering of the seismometer array deployment area which permits analysis of surface waves, receiver functions, surface wave azimuthal anisotropy, and shear-wave splitting in the area. Results provide insights into the local seismic structure of 40 to 50 million-year-old Pacific lithosphere and will answer questions about whether this area conforms to predictions from models of normal lithospheric plate cooling or if secondary processes, such as small-scale mantle convection, are impacting plate behavior and crustal/mantle structure. Results will be tested against predictions for a suite of mantle flow conditions and mineral alignment/anisotropy modes. The project will also use the newly collected surface wave data to improve global surface wave dispersion maps, reducing imaging biases in the global dataset that result, in part, from uneven data coverage in the study area. The ocean bottom seismometer array covers an area for which there is inadequate data for the Pacific Array as identified by the global community of seismologists. These data will serve a large global community of seismologists that conduct global tomographic and other studies that examine shallow and deep-Earth heterogeneity and processes that help us better understand how the Earth works and the impacts deep seated mantle-driven processes can have on Earth's surface. The work complements that recently carried out by an international, collaborative, group of US, UK, German, and French scientists in the Atlantic Ocean, which makes possible a comparison of results between both ocean basins.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.

了解海底的结构以及板块构造如何导致俯冲带的板块运动、火山活动和巨型逆冲地震，对于了解各种类型的地质灾害及其触发因素非常重要。这些知识对于规划和了解如何减轻和/或尽量减少灾害（例如近年来在泰国和日本发生的灾害）的影响至关重要。全球地震层析成像利用地震和其他地球运动产生的地震信号对地球深层结构进行成像，长期以来一直是成像和了解地球内部结构及其变形方式的首选工具。为此，目前的断层扫描图像表明，美国大陆和夏威夷之间区域的东北太平洋板块比现有海洋板块模型预测的更为复杂。因为这个明显非典型的区域远离任何类型的已知热特征，例如大洋中脊或热点（即热量集中上涌，从而形成来自地球深处的岩浆，如形成夏威夷群岛的岩浆）必须有不同的机制在起作用。由于目前东北太平洋缺乏地震记录站，该地区地壳和下伏地幔结构的分辨率尚未得到充分解决，可能导致关于太平洋板块随时间演化的误导性理论。这项研究通过部署 25 个海底地震仪阵列长达 15 个月来捕获和记录来自地球运动的地震信号来解决这个问题。这些数据将有助于确定真实的结构，并将针对太平洋板块已有 40-5000 万年历史的部分。这些新的地震数据将允许探索当地的地震各向异性（不均匀的矿物/地壳结构方向）。当地幔矿物与地幔流动方向一致或当板块（例如太平洋板块）对其边缘的牵引力做出反应时，就会形成各向异性。因此，对地震各向异性的分析使科学家能够探索形成、移动并最终导致地球构造板块俯冲的地幔过程。该项目的更广泛影响包括最先进的海上地球物理和陆上地震处理和建模方面的研究生和博士后培训。本科生将参与特殊项目。这项工作补充了其他国际全球地震学工作，并涉及与英国、德国和法国科学家的合作。这项工作通过支持两名性别在科学领域代表性不足的研究人员，扩大了科学领域代表性不足的群体的参与，他们成为学生和其他地球科学家的榜样。这项研究提供了对地震和其他地球物理数据的综合分析，以阐明其结构美国中部太平洋板块无月山海山以西 600 公里宽的区域中洋壳、岩石圈和软流圈的分布、异质性和动力学大陆和夏威夷。地震数据将使用 25 个海底地震仪阵列收集。研究目标包括区域研究，覆盖地震仪阵列部署区域，允许分析该区域的表面波、接收器函数、表面波方位各向异性和剪切波分裂。结果提供了对 40 至 5000 万年前太平洋岩石圈局部地震结构的深入了解，并将回答该区域是否符合正常岩石圈板块冷却模型的预测，或者是否存在次生过程（例如小规模地幔对流）的问题。正在影响板块行为和地壳/地幔结构。结果将根据一系列地幔流条件和矿物排列/各向异性模式的预测进行测试。该项目还将使用新收集的表面波数据来改进全球表面波色散图，减少全球数据集中的成像偏差，这些偏差在一定程度上是由于研究区域数据覆盖不均匀造成的。全球地震学家界认为，海底地震仪阵列覆盖的太平洋阵列数据不足的区域。这些数据将为全球范围内的地震学家提供服务，他们进行全球断层扫描和其他研究，检查地球浅层和深层的异质性和过程，帮助我们更好地了解地球的运作方式以及深层地幔驱动的过程可能对地球表面产生的影响。这项工作补充了最近由美国、英国、德国和法国科学家组成的国际合作小组在大西洋开展的工作，使两个大洋盆地之间的结果进行比较成为可能。该奖项反映了 NSF 的法定使命，并已通过使用基金会的智力优点和更广泛的影响审查标准进行评估，认为值得支持。