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

由于大部分大陆地壳被冰覆盖，人们对南极洲的地质结构和历史知之甚少。在这里，pi将分析在南极洲的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一些特征，包括由于西南极洲的裂谷作用导致的地壳变薄，与造山有关的结构，以及不同构造块之间的边界。这些模型将与地质学上更好地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。地表热流将被绘制出来，并用于确定南极洲冰盖底部可能融化的地区。这种融化可以减少摩擦，降低对冰盖移动的阻力。这些模型将有助于确定地球对冰质量变化的反应是发生在几十年、几百年还是几千年。根据地震数据计算出的地幔黏度的估计值将用于更好地理解固体地球对南极洲不同地区冰质量变化的响应模式和时间尺度。这项研究将通过使用不同但互补的方法构建两个新的地震模型和一个热模型，提高我们对南极洲结构的认识。由于不同地震分析方法的局限性，将努力分为两种模式，一种是在仪器测量区域的200公里深度范围内寻求尽可能高的分辨率（贝叶斯蒙特卡罗联合反演），另一种是确定整个大陆和通过地幔过渡带延伸的周围海洋的结构（伴随全波形反演）。蒙特卡罗反演将联合反演地震和环境噪声相关的瑞利波群和相速度，以及p波接收函数和瑞利H/V比。反演将在贝叶斯框架中完成，该框架为结构模型提供不确定性估计。方位各向异性将由瑞利波速确定，提供对地幔结构和流动模式的约束。地震数据也将反演温度结构，提供岩石圈厚度和地表热流的估计。更大规模的模型将覆盖整个大陆以及周围的海洋，并将使用谱元法在三维地球模型中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。该模型可拟合包括体波、基波和高模面波在内的所有波形。采用双差分方法，结合环境噪声互相关格林函数，同时求解径向和方位各向异性，可以获得更高的分辨率。该奖项反映了美国国家科学基金会的法定使命，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。

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.