Collaborative Research: Antarctic Seismic Investigations of ULVZ Structure

合作研究：南极 ULVZ 结构地震调查

• 批准号: 1643551
• 负责人: Samantha Hansen
• 金额: $ 10.83万
• 依托单位: University of Alabama Tuscaloosa
• 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 2020-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1643551&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和流体外核交界处顶部的超低速带(ULVZ)。ULVZ之所以这样命名，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ULVZ被认为与融化过程有关，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扮演的角色，人们越来越多地存在争议。ULVZ可能包括地球内部最大的岩浆室。目前，研究人员只在地球核地幔边界的40%范围内搜索了ULVZ，该项目将使用现有的地震数据来绘制南极洲下方未勘探区域的地图，并解释ULZZ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。项目成果将发表在科学期刊上，在科学博览会上展示，并通过研究人员的网站进行交流。研究团队还将参加由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。技术项目描述国家研究委员会强调，核幔边界(CMB)结构的高分辨率成像是地球科学中一个高度优先的新兴研究机会，因为CMB沿线的异常可能在我们地球的热和化学演化中发挥关键作用。特别令人感兴趣的是超低速带(ULVZ)，与地震速度显著降低和密度增加有关的横向变化的薄边界层，就在CMB上方。关于ULVZ的起源存在许多问题，但对最低地幔的不完全地震采样限制了我们详细绘制全球ULVZ结构图的能力。利用最近从南极横贯北极山脉北部网络(TAMNNET)收集的数据，该项目将使用岩心反射地震震相(SCP、PCP和SCS)来调查沿CMB以前未勘探的部分是否存在ULVZ。数据样本包括太平洋大剪切速度省(LLSVP)的南部边界，这是全球剪切波层析模型的主要特征，并将使研究人员能够检查ULVZ和LLSVP之间的可能联系。该项目的主要目标是：1)使用TAMNNET数据，通过基于阵列的方法，记录在以前未被勘探的最低地幔区域的ULVZ的存在/不存在；2)使用一维和2.5维波传播工具对数据进行模拟，以获得ULVZ的性质并评估模型之间的权衡；3)使用高质量的事件，用地理分布更分散、开放访问的南极站的数据来增加密集分布的TAMNNET数据，以通过单站分析增加CMB的覆盖面；以及4)探索超低空区域解模型对起源、现代动力学和演化的影响，包括它们与其他深部地幔结构的联系，例如低深地幔结构。该项目旨在为超低空区域提供新的约束，包括它们与低低深地幔的潜在联系，从而与其他专注于地球内部过程的地震和地球动力学研究有关？S。该项目将促进阿拉巴马大学(UA)和亚利桑那州立大学(ASU)之间的一项新的研究合作，每一项合作都为该倡议带来了独特的优势。

项目成果

Investigating Ultra-low Velocity Zones in the Southern Hemisphere Using ScP Waveforms

使用 ScP 波形研究南半球的超低速区

• 发表时间: 2018
• 期刊: American Geophysical Untion
• 作者: Carson, S.E.;Hansen, S.E.;Garnero, E.;Yu, S.
• 通讯作者: Yu, S.

Investigating Ultra-low Velocity Zones beneath the Southwestern Pacific

调查西南太平洋下方的超低速区

• 发表时间: 2017
• 期刊: American Geophysical Union
• 作者: Carson, S.E.;Hansen, S.E.
• 通讯作者: Hansen, S.E.

Expanding Ultra-low Velocity Zone Investigations in the Southern Hemisphere using Seismic Data from Antarctica

利用南极洲地震数据扩大南半球超低速区调查

• 发表时间: 2019
• 期刊: American Geophysical Union
• 作者: Hansen, Samantha;Carson, Sarah;Garnero, Edward;Yu, Shule;Rost, Sebastian
• 通讯作者: Rost, Sebastian

Investigating ultra-low velocity zones in the southern hemisphere using an Antarctic dataset

• DOI: 10.1016/j.epsl.2020.116142
• 发表时间: 2020-04-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Hansen, Samantha E.;Carson, Sarah E.;Yu, Shule
• 通讯作者: Yu, Shule