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位于地球内部固体地幔及其流体外核之间边界顶部的超值速度区（ULVZ）。 乌尔维兹之所以如此命名，是因为当遇到这些区域时，地震波穿过地球会急剧下降。尽管ULVZ被认为与熔化过程有关，但关于它们的起源以及它们在我们星球的热和化学演化中所起的作用越来越有争议。 Ulvzs可能包括地球内部最大的岩浆室。目前，研究人员仅搜索了地球核心掩盖边界的40％，以供ULVZ搜索，该项目将使用现有的地震数据来绘制南极下未开发的区域并解释ULVZ的性质。该项目将支持两名研究生，并为本科参与创造机会。 项目结果将在科学期刊上发表，在科学博览会上发表，并通过研究人员的网站进行沟通。研究团队还将参加NSF赞助的PolarTrec（探索和协作）计划，以将科学传达给学生和更广泛的社区。 技术项目描述国家研究委员会强调了核心助是边界（CMB）结构的高分辨率成像，因为CMB沿线的异常可能在我们星球的热和化学演化中起关键作用，因此在地球科学中是一种高优先级的研究机会。特别令人感兴趣的是超低速度区（ULVZ），横向变化的边界层与急剧的地震速度相关，密度降低并增加，而密度则在CMB上方。 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。 该项目使用最近收集的来自南极洲北部北部网络（TAMNNET）的数据，该项目将使用核心反射的地震阶段（SCP，PCP和SCS）来研究CMB的先前未开发的部分的ULVZ存在/不存在。 数据采样包括Pacific大型低剪力速度省（LLSVP）的南部边界，这是全球剪力波断层扫描模型中的主要特征，并将允许研究人员检查ULVZS和LLSVPS之间的可能联系。该项目的主要目标是：1）使用Tamnnet数据记录以基于数组的方法的先前未开发的最低地幔的未开发区域中的ULVZ存在/不存在； 2）用1-和2.5-D波传播工具对数据进行建模，以获取ULVZ属性并评估模型之间的权衡； 3）使用高质量的事件来增强较密集的TAMNNET数据，并从更高地理分布的开放式访问南极站中使用这些数据，以通过单站分析来增加CMB的覆盖范围； 4）探索ULVZ解决方案模型对起源，当今动态和进化的含义，包括它们与其他深层结构的联系，例如LLSVP。该项目旨在为ULVZ提供新的限制，包括与LLSVPS的潜在联系，从而与其他地震和地震动态研究有关，将其与其他地震和地球性研究有关。该项目将促进阿拉巴马大学（UA）和亚利桑那州立大学（ASU）之间的新研究合作，每个大学都为该计划带来了特定的优势。