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仍然知之甚少。在这里，PI 将分析南极洲众多项目记录的超过 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包括西南极洲裂谷导致的地壳减薄、与造山相关的结构以及不同构造块之间的边界等特征。这些模型将与地质学上更容易理解的大陆进行比较，以限制南极洲的构造演化。此外，这项工作还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识别南极洲冰盖底部可能融化的区域。这种融化可以减少摩擦并降低冰盖运动的阻力。 这些模型将有助于确定地球对冰块变化的反应是否会发生数十年、数百年或数千年。根据地震数据计算出的地幔粘度估计值将用于更好地了解固体地球对南极洲各地冰块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热模型来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，工作将分为两个模型，一个是在仪器仪表区域上部200公里深度内寻求尽可能最高分辨率的模型（贝叶斯蒙特卡罗联合反演），另一个模型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（伴随全波形反演）。 蒙特卡罗反演将联合反演来自地震的瑞利波群和相速度以及环境噪声相关性以及 P 波接收器函数和瑞利 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度确定，从而对地幔结构和流动模式提供约束。地震数据还将针对温度结构进行反演，提供岩石圈厚度和表面热流的估计。更大规模的模型将覆盖整个大陆以及周围的海洋，并将使用三分量地震图之间的相位差的伴随反演和使用谱元方法在3D地球模型中计算的合成地震图来构建。该模型将拟合整个波形，包括体波以及基波和高模表面波。通过使用双差法并结合环境噪声互相关的格林函数，并求解径向和方位各向异性，可以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智力优点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.