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：南极冰盖下的地质为其移动的冰川系统提供了一个关键条件：一个脆弱的，多孔的，可能含水的沉积层提供了一个光滑的床，而接触处的坚硬基岩可能会减少冰流。然而，了解地质情况是非常困难的，因为这片大陆很偏远，冰层很厚。使用部署在冰盖顶部的地震站提供了一种通过冰层观察大陆的替代工具，因为它们记录的地震信号包含有关冰盖底部和下面地壳地质的敏感信息。例如，厚而多孔的沉积层将导致地震波传播得更慢。在这个项目中，调查人员将1）利用过去18年在南极洲200多个地点收集的地震数据，2）使用一套现代地震数据分析工具来产生各种地震信号，以及3）将它们转化为关于物理性质的映射集（例如地震波的速度）和下伏地壳的化学成分（例如二氧化硅含量）。这些地震速度图，与不确定性测量量化的准确性，提供了一个一阶评估冰下沉积层的分布。其他信息，如其他地壳性质和推断的化学成分下，这些网站将进一步阐明地质演变的大陆埋在厚厚的冰盖。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冰下地壳的热剖面。 第二部分：南极冰盖下地壳从冰冻圈和岩石圈的角度来看都具有重要意义：在局部和区域尺度上，南极冰盖底部的浅部物理性质为快速移动的冰盖动力学提供了重要的边界条件;在更大的尺度上，体系结构（厚度和泊松比）整个大陆变化的地壳保留了过去地质演化的特征，其化学成分对地热有很大贡献。结构然而，由于该大陆的偏远和厚厚的冰层覆盖，这些特性尚未得到系统的研究。在这项拟议的研究中，研究人员将分析来自200多个永久性和便携式地震站的18年地震记录，以限制冰下地震结构，地壳结构，并利用多种地震技术对大块地壳的化学成分进行研究。他们的分析将包括：1）系统测量环境噪声和地震的宽频带Rayleigh波水平-垂直比（H/V），2）分析高频接收函数波形和两层h-k叠加，提供泊松比和冰下结构面深度信息，3）测量Love波频散和反演径向各向异性，4）研究地震波的频散和各向异性。4）环境噪声和地震的瑞利波方位各向异性测量：5）瑞利波频散、H/V比和接收函数波形的联合解释，以获得详细的冰下各向同性结构; 6）所有地震各向异性测量的Monte Carlo横向各向同性（TTI）建模。将把这些分析综合在一起，以产生一套可交付的地震数据，包括确定具有分级分辨率的冰下沉积物厚度图、更准确地确定地壳厚度和泊松比，以及量化地壳组成。拟议的工作将满足两个主要的科学目标。第一，它将提供关于南极冰盖底部接触和地震站地点沉积厚度的详细资料，改进冰盖模型的边界条件，并确定南极洲内主要沉积盆地的位置。第二，对南极地壳厚度和组成的限制将提高对该大陆地质历史的认识。值得注意的是，地壳结构和组成将进一步促进未来对形成南极洲的各种构造过程的地质调查，如裂谷，岩石圈移动，造山运动和造山运动。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

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