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.

非技术项目描述本研究将研究位于地球内部固体地幔和流体外核边界顶部的超低速度带（ULVZs）。ulvz之所以如此命名，是因为地震波穿过地球时遇到这些区域时速度会急剧减慢。虽然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化学演化中所起的作用，争议越来越大。ulvz可能包括地球内部最大的岩浆库。目前，研究人员只在地球核心-地幔边界的40%的地方进行了ulvz的搜索，该项目将使用现有的地震数据来绘制南极洲未开发区域的地图，并解释ulvz的性质。该项目将支持两名研究生，并为本科生的参与创造机会。项目结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。研究团队还将参加美国国家科学基金会赞助的PolarTREC（教师和研究人员探索和合作）项目，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，地核-地幔边界（CMB）结构的高分辨率成像是地球科学中一个高优先级的新兴研究机会，因为CMB的异常可能在我们星球的热化学演化中起着关键作用。特别令人感兴趣的是超低速度带（ULVZs），这是一种薄的横向变化边界层，与CMB上方的地震速度急剧下降和密度增加有关。关于ULVZ的起源存在许多问题，但最下层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。利用最近从南极洲横贯南极山脉北部网络（TAMNNET）收集的数据，该项目将使用核心反射地震相位（ScP， PcP和ScS）来调查CMB以前未勘探过的部分的ULVZ存在/不存在。数据采样包括太平洋大低剪切速度省（LLSVP）的南边界，这是全球横波层析模型的主要特征，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，用基于阵列的方法记录以前未勘探过的最下层地幔区域的ULVZ存在/不存在；2)使用1维和2.5维波传播工具对数据进行建模，以获得ULVZ特性，并评估模型之间的权衡；3)利用高质量事件与地理分布更广、开放获取的南极站数据增强密集空间的TAMNNET数据，以增加单站分析的CMB覆盖；4)探索ULVZ解模型对起源、现今动力学和演化的意义，包括它们与其他深部地幔结构（如llsvp）的联系。该项目旨在为ulvz提供新的限制条件，包括它们与llsvp的潜在联系，从而与其他地震和地球动力学调查相关，这些调查主要关注地球内部的过程。室内。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，双方都为该计划带来了各自的优势。

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