Comprehensive Seismic and Thermal Models for Antarctica and the Southern Oceans: A Synthesis of 15-years of Seismic Exploration

南极洲和南大洋的综合地震和热模型：15 年地震勘探的综合

• 批准号: 1744883
• 负责人: Douglas Wiens
• 金额: $ 17.26万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-07-01 至 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1744883&HistoricalAwards=false
• 关键词: Comprehensive; Seismic; Thermal; Models; Antarctica

The geological structure and history of Antarctica remains poorly understood because much of the continental crust is covered by ice. Here, the PIs will analyze over 15 years of seismic data recorded by numerous projects in Antarctica to develop seismic structural models of the continent. The seismic velocity models will reveal features including crustal thinning due to rifting in West Antarctica, the structures associated with mountain building, and the boundaries between different tectonic blocks. The models will be compared to continents that are better understood geologically to constrain the tectonic evolution of Antarctica. In addition, the work will provide better insight into how the solid earth interacts with and influences the development of the ice sheet. Surface heat flow will be mapped and used to identify regions in Antarctica with potential melting at the base of the ice sheet. This melt can lead to reduced friction and lower resistance to ice sheet movement. The models will help to determine whether the earth response to ice mass changes occurs over decades, hundreds, or thousands of years. Estimates of mantle viscosity calculated from the seismic data will be used to better understand the pattern and timescales of the response of the solid earth to changes in ice mass in various parts of Antarctica.The study will advance our knowledge of the structure of Antarctica by constructing two new seismic models and a thermal model using different but complementary methodologies. Because of the limitations of different seismic analysis methods, efforts will be divided between a model seeking the highest possible resolution within the upper 200 km depth in the well instrumented region (Bayesian Monte-Carlo joint inversion), and another model determining the structure of the entire continent and surrounding oceans extending through the mantle transition zone (adjoint full waveform inversion). The Monte-Carlo inversion will jointly invert Rayleigh wave group and phase velocities from earthquakes and ambient noise correlation along with P-wave receiver functions and Rayleigh H/V ratios. The inversion will be done in a Bayesian framework that provides uncertainty estimates for the structural model. Azimuthal anisotropy will be determined from Rayleigh wave velocities, providing constraints on mantle fabric and flow patterns. The seismic data will also be inverted for temperature structure, providing estimates of lithospheric thickness and surface heat flow. The larger-scale model will cover the entire continent as well as the surrounding oceans, and will be constructed using an adjoint inversion of phase differences between three component seismograms and synthetic seismograms calculated in a 3D earth model using the spectral element method. This model will fit the entire waveforms, including body waves and both fundamental and higher mode surface waves. Higher resolution results will be obtained by using double-difference methods and by incorporating Green's functions from ambient noise cross-correlation, and solving for both radial and azimuthal anisotropy.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.

南极洲的地质结构和历史仍然知之甚少，因为大部分大陆地壳被冰覆盖。在这里，PI将分析南极洲许多项目记录的超过15年的地震数据，以开发该大陆的地震结构模型。 地震速度模型将揭示南极洲西部由于裂谷而导致的地壳变薄、与造山运动有关的结构以及不同构造块体之间的边界等特征。这些模型将与地质学上更好理解的大陆进行比较，以限制南极洲的构造演化。此外，这项工作将更好地了解固体地球如何与冰盖相互作用并影响冰盖的发展。将绘制地表热流图，并用于确定南极洲冰盖底部可能融化的区域。这种融化可以导致摩擦力减少和冰盖运动阻力降低。 这些模型将有助于确定地球对冰量变化的反应是发生在几十年、几百年还是几千年之后。根据地震数据计算出的地幔粘性估计数将用于更好地了解固体地球对南极洲各地冰量变化的反应模式和时间尺度，这项研究将通过使用不同但互补的方法建立两个新的地震模型和一个热模型，增进我们对南极洲结构的了解。由于不同地震分析方法的局限性，将在两种模式之间进行努力，一种是在仪器配备良好的区域的200公里深度内寻求最高分辨率的模式（贝叶斯蒙特-卡罗联合反演），另一种是确定整个大陆和延伸穿过地幔过渡带的周围海洋的结构的模式（伴随全波形反演）。 蒙特-卡罗反演将联合反演地震的瑞利波群速度和相速度以及环境噪声相关性，沿着P波接收器函数和瑞利H/V比。反演将在贝叶斯框架中进行，该框架为结构模型提供不确定性估计。方位各向异性将确定从瑞利波速度，提供地幔结构和流动模式的约束。还将对地震数据进行温度结构反演，提供岩石圈厚度和地表热流的估计。较大比例的模型将覆盖整个大陆以及周围的海洋，并将使用三维地球模型中使用谱元法计算的三分量地震图和合成地震图之间的相位差的伴随反演来构建。该模型将拟合整个波形，包括体波以及基波和高模表面波。通过使用双差方法和结合来自环境噪声互相关的绿色函数以及求解径向和方位各向异性，将获得更高分辨率的结果。该奖项反映了NSF的法定使命，并通过使用基金会的知识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 Crust and Upper Mantle Structure of Central and West Antarctica From Bayesian Inversion of Rayleigh Wave and Receiver Functions

• DOI: 10.1029/2017jb015346
• 发表时间: 2018-09
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: W. Shen;D. Wiens;S. Anandakrishnan;R. Aster;P. Gerstoft;P. Bromirski;S. Hansen;I. Dalziel;D. Heeszel;A. Huerta;A. Nyblade;R. Stephen;Terry J. Wilson;J. P. Winberry

Seismic Structure of the Antarctic Upper Mantle Imaged with Adjoint Tomography

• DOI: 10.1029/2019jb017823
• 发表时间: 2020-03
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: A. Lloyd;D. Wiens;H. Zhu;J. Tromp;A. Nyblade;R. Aster;S. Hansen;I. Dalziel;T. J. Wilson;E. Ivins;J. O’Donnell

A Geothermal Heat Flux Map of Antarctica Empirically Constrained by Seismic Structure

• DOI: 10.1029/2020gl086955
• 发表时间: 2020-07
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: W. Shen;D. Wiens;A. Lloyd;A. Nyblade

Solid Earth change and the evolution of the Antarctic Ice Sheet

• DOI: 10.1038/s41467-018-08068-y
• 发表时间: 2019-01
• 期刊: Nature Communications
• 影响因子: 16.6
• 作者: P. Whitehouse;N. Gomez;M. King;D. Wiens