Crustal and Uppermost Mantle Anisotropy From Seismic Ambient Noise Data Observed on EarthScope/USArray

知识内容和优点这项研究旨在开发一种新的地震层析成像方法，称为“Eikonal层析成像”，并将其应用于在EarthScope/US阵列上记录的环境噪声和地震数据，以推断美国西部和中部地壳和最上地幔的径向和方位各向异性结构。该方法基于将包括可移动阵列、灵活阵列和ANSS主干在内的US阵列显式地视为阵列，以便跟踪在其上传播的面波。由此产生的“相移时间面”对面波的传播速度和方向施加了局部约束，直接揭示了方位各向异性和随之而来的不确定性。等径向层析成像是面波层析成像技术的重大改进：它不受特殊正则化的影响，无需迭代就能准确跟踪大圆外几何波，提供准确的误差估计，并对方位各向异性提供直接的局部约束。该方法被应用于从2004年到2010年在美国阵列上观测到的环境噪声数据，以估计从6秒到40秒的各向同性和方位向各向异性相速度。这些观测结果是提出的地壳和上地幔的径向和方位各向异性的3DVS模型的基础。这种方法正在推广到Love波和地震数据(以提供更多关于地幔的信息)。最终结果涵盖了美国，西起太平洋，东至大平原。该项目的目标是提高对地壳和地幔顶部各向异性的理解，这是了解地壳和地幔变形历史的关键。如果没有新的方法(环境噪声层析成像、Eikonal层析成像)和独特的地震观测工具(US阵列)的融合，各向异性的3D模型的开发是不可能的。数据处理和反演方法为研究生提供了独特的教育体验。知识分子。这项研究提供了从地幔各向异性中分辨地壳的能力，有助于澄清SKS分裂的解释。预计对区域尺度的构造以及美国西部和中部之下的变形状态的研究也将产生重大影响，进而扩展到世界其他地方类似的大陆地区。此外，随着其他区域阵列的安装，所开发的方法也适用于世界其他地方；例如，在欧洲和中国以及用于PASSCAL实验。研究团队在向广泛社区提供数据产品、模型、软件和培训方面有着良好的记录。地球望远镜：这项研究正在帮助实现美国地球阵列的愿景--以前所未有的细节模拟美国下面的地球--并旨在为实现美国地震界对地球望远镜/美国阵列的愿景做出贡献。

Intellectual Content and MeritThis research aims to develop a new method of seismic tomography called "Eikonal tomography" and apply it to ambient noise and earthquake data recorded on EarthScope/USArray to infer the radial and azimuthal anisotropy structure of the crust and uppermost mantle across the western and central US. The method is based on treating the USArray, including the Transportable Array, the Flexible Array, and the ANSS backbone, explicitly as an array in order to track surface waves that propagate across it. The resulting "phase travel time surfaces" place local constraints on the speed and direction of travel of surface waves, directly revealing azimuthal anisotropy with attendant uncertainties. Eikonal tomography represents a significant improvement in surface wave tomography: it is free from ad-hoc regularization, accurately tracks off-great-circle geometrical waves without iteration, provides accurate error estimates, and presents direct local constraints on azimuthal anisotropy. The method is being applied to ambient noise data observed on the USArray from 2004 through 2010 to estimate isotropic and azimuthally anisotropic phase speeds from 6 sec to 40 sec period. These observations are the basis for the proposed radially and azimuthally anisotropic 3D Vs model of the crust and uppermost mantle. The method is being generalized to Love waves and earthquake data (to provide more information about the mantle). The final results encompass the US from the Pacific in the west through the Great Plains in the east.The goal of the project is to improve understanding of crustal and uppermost mantle anisotropy, which holds a key to knowledge of the deformation history of the crust and mantle. The development of the 3D model of anisotropy would be impossible without the confluence of new methodology (ambient noise tomography, Eikonal tomography) and a unique seismic observational tool (USArray).Broader ImpactsEducational. The data processing and inversion methodology offers a unique educational experience for a graduate student. Intellectual. The ability to resolve crustal from mantle anisotropy provided by the research helps to clarify the interpretation of SKS-splitting. Significant impacts also are anticipated on studies of regional-scale tectonics as well as the deformational state beneath the western and central US and, by extension, similar continental regions elsewhere in the world. Moreover, the methods developed are applicable elsewhere in the world as other regional arrays are installed; e.g., in Europe and China and for PASSCAL experiments. The research team has a strong track record of making data products, models, software, and training available to a wide community. EarthScope: The research is helping to achieve the vision of the USArray -- modeling the Earth beneath the US in unprecedented detail -- and aims to contribute to achieving the US seismological community's vision for EarthScope/USArray.