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在俯冲带中引起板块运动，火山和大型地震的板块构造工作的作用，对于理解各种类型的地质阵亡以及触发它们的原因很重要。这些知识对于为了计划和理解如何减轻和/或最大程度地减少灾难的影响，例如近年来在泰国和日本发生的知识至关重要。全球地震层析成像使用地震和其他地球运动的地震信号来图像地球的深层结构，一直是选择和理解地球内部结构及其变形的选择的工具。为此，当前的层析成像图像表明，美国大陆和夏威夷之间的东北太平洋板块比当前海洋板模型所预测的要复杂。因为这个显然是非典型的区域远非远非任何已知的热特征，例如中山脊或热点（即，浓缩的热量上升流，因此像夏威夷岛形成的岩浆一样，从地球深处）必须采取不同的机制。由于目前在东北太平洋地区缺乏地震记录站，该地区的地壳和潜在地幔结构的分辨率尚未解决，并且可能导致了对太平洋板块如何随着时间而演变的误导理论。这项研究通过部署一系列25个海洋底部地震米15个月来捕获和记录地球运动的地震信号，从而解决了这一问题。这些数据将允许确定实际结构，并将其针对400至5000万年历史的太平洋板块的一部分。这些新的地震数据将允许探索局部地震各向异性（非均匀的矿物/地壳结构取向）。当地幔矿物与地幔流动方向对齐时，或当太平洋板等板对沿其边缘拉扯的力响应时，各向异性形成。因此，对地震各向异性的分析使科学家可以探索形成，移动和最终导致地球构造板的俯冲的地幔过程。该项目的更广泛影响包括研究生和最先进的地球物理和陆上地震加工和建模的博士后培训。本科生将参与特殊项目。这项工作补充了其他国际地震学的努力，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研究人员，他们的性别在科学中的人数不足，并作为学生和其他地球科学家的榜样，从而扩大了科学中代表性不足的群体的参与。这项研究提供了地震和其他地球物理学数据的综合分析，这些分析将阐明结构，杂物和动态范围，以阐明〜在美国大陆和夏威夷之间的太平洋板块上的无月山区山脉以西。地震数据将使用25个海洋底部地震米阵列收集。研究目标包括一项区域研究，涵盖地震计阵列部署区域，该区域允许对表面波，接收器功能，表面波方位角各向异性分析以及该区域的剪切波分裂。结果提供了对40至5000万年历史的太平洋岩石圈的局部地震结构的见解，并将回答有关该区域是否符合正常岩石圈板冷却模型的预测或次级过程（例如小规模地幔对流）的问题，会影响板块的行为和甲壳/地面结构。将测试结果，以预测一套地幔流条件和矿物比对/各向异性模式。该项目还将使用新收集的表面波数据来改善全局表面波分散图，从而减少全球数据集中的成像偏差，部分原因是研究区域的数据覆盖率不均匀。海洋底部地震计阵列涵盖了一个区域，该区域的数据不足，太平洋阵列被全球地震学家社区所确定的区域。这些数据将为一个全球大型的地震学家社区服务，这些社区进行全球层析成像和其他研究，这些研究检查浅和深地球的异质性和过程，这些过程有助于我们更好地了解地球的运作方式以及深层地幔驱动的进程的影响可能会对地球表面产生。这项工作是由国际，合作，我们中的我们，英国，德语和法国科学家最近在大西洋进行的，这使得这两个海洋盆地之间的结果可以比较。这项奖项反映了NSF的法定任务，并被认为是值得通过基金会的智力和更广泛影响的评估来通过评估来进行支持的。