Collaborative Research: Antarctic Seismic Investigations of ULVZ Structure

合作研究：南极 ULVZ 结构地震调查

• 批准号: 1643387
• 负责人: Edward Garnero
• 金额: $ 7.26万
• 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: 2017
• 资助国家: 美国
• 起止时间: 2017-03-01 至 2019-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1643387&HistoricalAwards=false
• 关键词: Collaborative; Research; Antarctic; Seismic; Investigations

Non-Technical Project DescriptionThis research will study Ultralow Velocity Zones (ULVZs), located in Earth's interior on top of the boundary between the Earth's solid mantle and its fluid outer core. The ULVZs are so named because seismic waves passing through the Earth slow down dramatically when they encounter these zones. While ULVZs are thought to be related to melting processes, there is growing controversy regarding their origin and the role they play in the thermal and chemical evolution of our planet. The ULVZs may include the largest magma chambers in Earth's interior. Currently, researchers have only searched 40% of Earth's core-mantle boundary for the ULVZs and this project would use existing seismic data to map an unexplored area under Antarctica and interpret the nature of the ULVZs. This project will support two graduate students and create opportunities for undergraduate involvement. Project results will be published in scientific journals, presented at science fairs, and communicated through the researchers' websites. The research team will also take part in the NSF-sponsored PolarTREC (Teachers and Researchers Exploring and Collaborating) program to communicate the science to students and the broader community. Technical Project DescriptionThe National Research Council has highlighted high-resolution imaging of core-mantle boundary (CMB) structure as a high-priority, emerging research opportunity in the Earth Sciences since anomalies along the CMB likely play a critical role in the thermal and chemical evolution of our planet. Of particular interest are ultralow velocity zones (ULVZs), thin laterally-varying boundary layers associated with dramatic seismic velocity decreases and increases in density that are seen just above the CMB. Many questions exist regarding the origin of ULVZs, but incomplete seismic sampling of the lowermost mantle has limited our ability to map global ULVZ structure in detail. Using recently collected data from the Transantarctic Mountains Northern Network (TAMNNET) in Antarctica, this project will use core-reflected seismic phases (ScP, PcP, and ScS) to investigate ULVZ presence/absence along previously unexplored sections of the CMB. The data sampling includes the southern boundary of the Pacific Large Low Shear Velocity Province (LLSVP), a dominant feature in global shear wave tomography models, and will allow the researchers to examine a possible connection between ULVZs and LLSVPs. The main objectives of the project are to: 1) use TAMNNET data to document ULVZ presence/absence in previously unexplored regions of the lowermost mantle with array-based approaches; 2) model the data with 1- and 2.5-D wave propagation tools to obtain ULVZ properties and to assess trade-offs among the models; 3) use high quality events to augment the densely-spaced TAMNNET data with that from the more geographically-distributed, open-access Antarctic stations to increase CMB coverage with single-station analyses; and 4) explore the implications of ULVZ solution models for origin, present-day dynamics, and evolution, including their connection to other deep mantle structures, like LLSVPs.The project aims to provide new constraints on ULVZs, including their potential connection to LLSVPs, and thus relates to other seismic and geodynamic investigations focused on processes within the Earth?s interior. This project will promote a new research collaboration between The University of Alabama (UA) and Arizona State University (ASU), each of which brings specific strengths to the initiative.

非技术项目描述这项研究将研究超低速带（ULVZ），位于地球内部的固体地幔和流体外核之间的边界顶部。 ULVZ之所以如此命名，是因为穿过地球的地震波在遇到这些区域时会急剧减慢。虽然超低空区被认为与融化过程有关，但关于其起源及其在地球热演化和化学演化中所起的作用的争议越来越大。ULVZ可能包括地球内部最大的岩浆库。目前，研究人员只搜索了地球内核-地幔边界的40%，该项目将使用现有的地震数据来绘制南极洲下未勘探区域的地图，并解释ULVZ的性质。该项目将支持两名研究生，并为本科生参与创造机会。 项目成果将在科学期刊上发表，在科学博览会上展示，并通过研究人员的网站进行交流。该研究小组还将参加NSF赞助的PolarTREC（教师和研究人员探索与合作）计划，向学生和更广泛的社区传播科学。 国家研究理事会强调了核幔边界（CMB）结构的高分辨率成像作为地球科学中的一个高优先级，新兴的研究机会，因为沿着沿着CMB的异常可能在我们星球的热演化和化学演化中发挥关键作用。特别令人感兴趣的是超低速区（ULVZ），即与CMB上方的地震速度急剧下降和密度增加相关的薄的横向变化边界层。 关于ULVZ的起源存在许多问题，但最低地幔的不完整地震采样限制了我们详细绘制全球ULVZ结构的能力。 利用最近从南极洲的跨南极山脉北方网络（TAMNNET）收集的数据，该项目将使用岩心反射地震相位（ScP、PcP和ScS）来调查沿CMB以前未勘探的沿着是否存在ULVZ。 数据采样包括太平洋大低剪切速度区（LLSVP）的南部边界，这是全球剪切波层析成像模型的主要特征，并将使研究人员能够检查ULVZ和LLSVP之间可能的联系。该项目的主要目标是：1）使用TAMNNET数据，通过基于阵列的方法记录以前未勘探过的最低地幔区域中是否存在ULVZ; 2）使用一维和2.5维波传播工具模拟数据，以获得ULVZ特性并评估模型之间的权衡; 3）使用高质量的事件，用来自地理分布更广、开放访问的南极站的数据来补充密集分布的TAMNNET数据，以增加CMB单站分析的覆盖范围;和4）探讨ULVZ的起源，现今的动力学和演化的解决方案模型的影响，包括他们的连接到其他深地幔结构，如LLSVP。该项目旨在提供新的约束ULVZ，包括其潜在的连接到LLSVP，从而涉及到其他地震和地球动力学调查集中在地球内部的过程？的内部。该项目将促进亚拉巴马大学（UA）和亚利桑那州立大学（ASU）之间的新的研究合作，每一个都为该计划带来了具体的优势。