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

知识内容和优点本研究旨在开发一种称为“Eikonal层析成像”的新地震层析成像方法，并将其应用于EarthScope/USArray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上地幔的径向和方位各向异性结构。该方法基于将 USArray（包括可移动阵列、柔性阵列和 ANSS 主干网）明确视为阵列，以便跟踪在其上传播的表面波。由此产生的“相位传播时间表面”对表面波的传播速度和方向施加局部约束，直接揭示方位各向异性以及随之而来的不确定性。 Eikonal 层析成像代表了表面波层析成像的重大改进：它无需进行临时正则化，无需迭代即可准确跟踪偏离大圆的几何波，提供准确的误差估计，并对方位各向异性提出直接的局部约束。该方法被应用于 2004 年至 2010 年在 USArray 上观测到的环境噪声数据，以估计 6 秒至 40 秒周期内的各向同性和方位各向异性相速度。这些观测结果是提出的地壳和上地幔径向和方位各向异性 3D Vs 模型的基础。该方法正在推广到勒夫波和地震数据（以提供有关地幔的更多信息）。最终结果涵盖了美国，从西部的太平洋到东部的大平原。该项目的目标是提高对地壳和上地幔各向异性的认识，这是了解地壳和地幔变形历史的关键。如果没有新方法（环境噪声断层扫描、Eikonal 断层扫描）和独特的地震观测工具 (USArray) 的融合，各向异性 3D 模型的开发是不可能的。更广泛的教育影响。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。该研究提供的从地幔各向异性解析地壳的能力有助于澄清 SKS 分裂的解释。预计对区域尺度构造以及美国西部和中部地下变形状态以及世界其他地区类似大陆地区的研究也会产生重大影响。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，在欧洲和中国进行 PASSCAL 实验。该研究团队在向广泛社区提供数据产品、模型、软件和培训方面拥有良好的记录。 EarthScope：这项研究正在帮助实现 USArray 的愿景——以前所未有的细节对美国下方的地球进行建模——并旨在为实现美国地震界对 EarthScope/USArray 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.