Plume Structure and Mantle Layering Beneath the South Pacific: Modeling Teleseismic Waveforms from Traditional and Floating Sensors

南太平洋下方的羽流结构和地幔分层：利用传统和浮动传感器模拟远震波形

• 批准号: 2341811
• 负责人: Frederik Simons
• 金额: $ 67.26万
• 依托单位: Princeton University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-01-15 至 2026-12-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2341811&HistoricalAwards=false
• 关键词: Plume; Structure; Mantle; Layering; Beneath

Besides formidable hazards to humans, earthquakes are sources of energy that help us image the Earth’s interior. Earth is a dynamic planet, its interior always in convective motion, and to understand it as a system, seismologists mine the information contained in the measurement of earthquake waves recorded by seismometers across the globe. An area of specific interest is Earth’s mantle below the Pacific, which is strewn with volcanoes, most of them underwater, but many present as oceanic islands such as Hawaii, Samoa, and Tahiti. The source region of these volcanoes is insufficiently known; in particular it is not clear at what depths in the mantle they originate. Part of the reason for the lack of clarity is that seismic observations across the oceans are very hard to obtain. A new type of instrument, MERMAID, is a free-floating “hydrophone”, essentially an underwater microphone, drifting with the deep ocean currents, that picks up earthquake waves, almost like traditional seismometers. In this project, the researchers will use recordings from about 65 of these new instruments to update Earth models based on our current state of knowledge about earthquakes and Earth’s interior. The results will be new and better images of the Earth’s interior, which can be linked back to the processes operating at depth and expressed as volcanism at the surface. These scientific modeling activities will contribute to the research education of undergraduate geosciences majors, a geophysics graduate student and a post-doctoral researcher, the researchers engage in community and capacity building by archiving, curating, and sharing the data with the public via national data centers.MERMAID was originally designed to capture compressional first-arriving “P”-wave arrivals. Preliminary research on new techniques for using this data has shown detail in the entire wave train that can be used for waveform modeling, allowing the researchers to go beyond simple travel-time picking. The researchers will further develop this new technique, and apply it to distant, or “teleseismic” events identified in the entire dataset returned by all the MERMAID instruments active in the global oceans today, and to integrate them into mantle wavespeed and impedance contrast models for Polynesia. The waveform modeling technique for tomography focuses on smooth wavespeed variations and relies on modeling the ``oceanic last mile'' of the teleseismic mantle wavefield via spectral-element mapping using a transfer-function approach. The impedance contrast modeling technique focuses on sharp contrasts in wave speed and density and uses precursors to surface-reflected seismic phases to produce images of deep reflectors of both mantle transition-zone and mid-mantle discontinuities. It is a wave-equation imaging method that involves reverse-time migration employing full-waveform tomographic models for wavefield extrapolation. The modeling takes into account all three components of the seismogram and is accompanied by detailed sensitivity and hypothesis tests to give confidence in interpretation of the physical nature of mantle discontinuities in relation to the mantle plumes that will hopefully be revealed from wavespeed structure mapping.This project is supported by the Geophysics Program and the Geoinformatics Program in the Division of Earth Sciences.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.

除了对人类的巨大危害外，地震还是帮助我们描绘地球内部的能量来源。地球是一个动态的行星，它的内部总是处于对流运动中，为了将它理解为一个系统，地震学家挖掘了地球仪记录的地震波测量中包含的信息。一个特别感兴趣的区域是太平洋下面的地幔，那里散布着火山，其中大部分在水下，但许多是海洋岛屿，如夏威夷，萨摩亚和塔希提岛。这些火山的起源地区还不清楚，特别是不清楚它们起源于地幔的什么深度。缺乏清晰度的部分原因是很难获得跨海洋的地震观测结果。一种新型的仪器MERMAID是一种自由浮动的“水听器”，本质上是一种水下麦克风，随着深海洋流漂流，几乎像传统的地震仪一样拾取地震波。在这个项目中，研究人员将使用大约65个新仪器的记录，根据我们目前对地震和地球内部的了解来更新地球模型。其结果将是地球内部新的和更好的图像，这可以联系到在深度运作的过程，并表示为表面的火山活动。 这些科学建模活动将有助于本科地球科学专业的研究教育，一名物理学研究生和一名博士后研究员，研究人员通过国家数据中心存档，管理和与公众共享数据，参与社区和能力建设。MERMAID最初设计用于捕获压缩首次到达的“P”波到达。对使用这些数据的新技术的初步研究已经显示了可用于波形建模的整个波列的细节，使研究人员能够超越简单的走时拾取。研究人员将进一步开发这种新技术，并将其应用于今天活跃在全球海洋中的所有MERMAID仪器返回的整个数据集中识别的遥远或“地震”事件，并将其整合到波利尼西亚的地幔波速和阻抗对比模型中。层析成像的波形建模技术侧重于平滑的波速变化，并依赖于通过使用传递函数方法的谱元素映射来模拟地幔地幔波场的“海洋最后一英里”。阻抗对比建模技术的重点是在波的速度和密度的鲜明对比，并使用前兆的表面反射地震相位产生的地幔过渡带和中地幔不连续的深反射层的图像。它是一种波动方程成像方法，涉及逆时偏移，采用全波形层析模型进行波场外推。该模型考虑了地震记录的所有三个组成部分，并伴随着详细的灵敏度和假设检验，以使解释地幔不连续性与地幔柱的物理性质具有信心，这些地幔柱有望从波速结构制图中揭示出来。该项目得到地球科学部地球物理计划和地理信息计划的支持。该奖项反映了NSF的基金会的使命是履行其法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。