Collaborative Research: Seismic Investigation of the Sub-ice Environment and Crustal Composition of Antarctica

合作研究：南极冰下环境和地壳组成的地震调查

• 批准号: 1945693
• 负责人: Douglas Wiens
• 金额: $ 11.92万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1945693&HistoricalAwards=false
• 关键词: Collaborative; Research; Seismic; Investigation; Sub

Part I: NontechnicalThe geology beneath the Antarctic Ice Sheet sets up a key condition to its moving glacial systems: a weak, porous, and possibly water bearing sedimentary layer provides a slippery bed, whereas hard basement rock at the contact may reduce the ice flow. Knowing the geology, however, has been extremely difficult since the continent is remote and the ice cover is thick. Using seismic stations deployed on top of the ice sheet provides an alternative tool to see the continent through the ice, as seismic signal they record contains sensitive information about the base of the ice-sheet and the geology of the crust below. For example, a thick and porous sedimentary layer will cause the seismic waves to travel more slowly. In this project, the investigators will 1) utilize the seismic data collected in the past 18 years at more than 200 sites in Antarctica, 2) perform a suite of modern seismic data analysis tools to produce a variety of seismic signals, and 3) translate them into sets of maps about the physical properties (such as the speed of the seismic wave) and chemical composition (such as silica content) of the underlying crust. These seismic speed maps, with accuracy quantified by uncertainty measurements, provide a first-order assessment to the distribution of the sub-ice sedimentary layer. Additional information such as other crustal properties and inferred chemical composition beneath these sites will further shed light on the geological evolution of the continent buried by the thick ice sheet. Notably, determining the silica content of the crust will help produce better estimates of the thermal profiles of the sub-ice crust. Part II: Technical DescriptionThe underlying crust of Antarctica Ice Sheet holds strong importance from perspectives of both cryosphere and lithosphere: at local and regional scale, the shallow physical properties at the base of the Antarctic Ice Sheet sets an important boundary condition for the dynamics of the fast moving ice sheet; at a greater scale, the architecture (thickness and Poissons ratio) of the crust that varies across the continent retains the signature of the past geological evolution and its chemical composition contributes significantly to the geothermal structure. However, these properties have not been systematically studied due to both the remoteness of the continent and its thick ice-coverage. In this proposed study, the investigators will analyze 18 years of seismic records from more than 200 permanent and portable seismic stations, to constrain the sub-ice seismic structure, crustal architecture, and draw implications on the chemical composition of the bulk crust using multiple seismic techniques. Their analysis will include: 1) systematic measurement of the broad-band Rayleigh wave horizontal-vertical ratios (H/V) from both ambient noise and earthquakes; 2) analysis of high frequency receiver function waveforms and 2-layer h-k stacking to provide information on Poissons ratio and the depth of sub-ice discontinuities; 3) measurement of Love wave dispersion and inversion for radial anisotropy; 4) measurement of Rayleigh wave azimuthal anisotropy from both ambient noise and earthquakes; 5) Joint interpretation of Rayleigh wave dispersion, H/V ratios, and receiver function waveforms for detailed sub-ice isotropic structure; 6) a Monte Carlo transversely isotropic (TTI) modeling of all seismic anisotropic measurements. These analyses will be combined and synthesized to produce a set of seismic deliverables including the determination of a map of thickness of the sub-ice sediments with hierarchical-resolution, more accurate crustal thickness and Poissons ratio determination, and quantification of crustal composition. The proposed work will meet two major scientific objectives. First, it will provide detailed information about the bottom contact of the Antarctic ice-sheet and sediment thickness at localities of seismic stations, improving the boundary conditions for the ice-sheet modeling and determining the locations of major sedimentary basins within Antarctica. Second, constraints on the thickness and composition of the Antarctic crust will improve the understanding of the geology history of the continent. Notably, the crustal architecture and composition will further facilitate future geological investigation to various tectonic processes that have shaped Antarctica, such as rifting, lithospheric removal, orogeny, and mountain building.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.

第一部分：非技术性的地质在南极冰盖下方，为其移动冰川系统设定了关键条件：弱，多孔，可能是含水的沉积层提供了湿滑的床，而接触的硬地下岩石可能会减少冰流。然而，自大陆很遥远并且冰盖厚度以来，了解地质一直非常困难。使用部署在冰盖顶部的地震站提供了一种替代工具，可以通过冰看到大陆，因为它们记录的地震信号包含有关冰淇淋底座和下面地壳的地质的敏感信息。例如，较厚的多孔沉积层会导致地震波的行进速度更慢。 In this project, the investigators will 1) utilize the seismic data collected in the past 18 years at more than 200 sites in Antarctica, 2) perform a suite of modern seismic data analysis tools to produce a variety of seismic signals, and 3) translate them into sets of maps about the physical properties (such as the speed of the seismic wave) and chemical composition (such as silica content) of the underlying crust.这些地震速度图具有通过不确定性测量来量化的准确性，为亚冰沉积层的分布提供了一阶评估。这些位置下面的其他信息，例如其他地壳特性和推断的化学成分，将进一步阐明厚冰盖埋葬的大陆的地质演化。值得注意的是，确定地壳的二氧化硅含量将有助于更好地估计子冰壳的热曲线。 第二部分：技术描述，南极冰盖的潜在地壳从冰冻圈和岩石圈的角度来看：在局部和区域尺度上，南极冰盖底部的浅色物理特性为快速移动冰盖的动力学设定了重要的边界条件；在较大的规模上，整个非洲大陆的地壳的结构（厚度和泊松比）保留了过去地质进化的特征及其化学成分对地热结构的贡献显着贡献。但是，由于大陆的偏远和厚厚的冰覆盖，这些特性尚未系统地研究。在这项拟议的研究中，研究人员将分析来自200多个永久和便携式地震站的18年地震记录，以限制使用多种地震技术的底冰地震结构，地壳结构和图形的影响。他们的分析将包括：1）从环境噪声和地震中对宽带雷利波水平垂直比（H/V）进行系统测量； 2）分析高频接收器函数波形和2层H-K堆叠，以提供有关泊松比和亚冰不连续性深度的信息； 3）测量径向各向异性的爱波散分散和反转； 4）从环境噪声和地震中测量瑞利波方位角各向异性； 5）用于详细的亚冰的各向同性结构的瑞利波分散，H/V比和接收器功能波形的联合解释； 6）所有地震各向异性测量值的蒙特卡洛横向各向同性（TTI）建模。这些分析将被合并和合成，以产生一组地震可交付成果，包括确定具有分层分辨率的亚冰沉积物厚度，更准确的地壳厚度和Poissons比率的确定以及地壳组成的量化。拟议的工作将达到两个主要的科学目标。首先，它将提供有关地震台站点南极冰盖和沉积物厚度的底部接触的详细信息，从而改善了冰盖建模的边界条件，并确定南极洲主要沉积盆地的位置。其次，对南极外壳的厚度和组成的约束将改善对非洲大陆地质历史的理解。值得注意的是，地壳建筑和构图将进一步促进未来对各种构造南极的构造过程的地质调查，例如裂谷，岩石圈去除，造山学和山区建筑。这项奖项反映了NSF的法定任务，并认为通过基金会的知识优点和广泛的crietia criteria criteria criperia crietia crietia crietia crietia crietia crietia crietia criteria rection the Approction均值得通过评估。

项目成果

The Seismic Structure of the Antarctic Upper Mantle

南极上地幔的地震结构

• DOI: 10.1144/m56-2020-18
• 发表时间: 2021
• 期刊: Memoirs
• 作者: Wiens, Douglas A.;Shen, Weisen;Lloyd, Andrew
• 通讯作者: Lloyd, Andrew

Radial Anisotropy and Sediment Thickness of West and Central Antarctica Estimated From Rayleigh and Love Wave Velocities

• DOI: 10.1029/2021jb022857
• 发表时间: 2022-03
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Zheng-Zheng Zhou-Zheng;D. Wiens;W. Shen;R. Aster;A. Nyblade;T. Wilson