New constraints on and models of global and plate-scale anisotropic mantle structure

该项目的目标是利用地震成像技术和广泛的地震观测，提高我们对地球内部大规模弹性结构的认识。这项研究将改进对地幔各向异性速度结构的描述，从而有助于解决目前地震学模型之间的重大差异。特别是，将研究过渡带和下地幔大尺度各向异性的存在和强度、深部地幔密度与弹性模量的相关性以及剪切速度和压缩速度变化的尺度关系。将收集表面波泛音频散的新测量值，这将诊断现有模式的有效性，这些模式表明太平洋软流层各向异性结构具有很强的变异性。该研究将阐明海洋岩石圈和软流圈径向各向异性和方位各向异性之间的关系。将进行两项相关调查。全球研究将建立在收集的数据集和开发的分析工具的基础上，以确定最近的全球模型S362ANI （Kustowski et al., 2008）。项目研究将从几个方面扩展这一早期工作，最重要的是：(1)包含正模中心频率和Q值，以更好地约束全球平均结构；(2)结合已发布的正模分裂函数，以解决过渡区和下地幔速度的非均质性和各向异性；(3)使用模型参数(波速、各向异性、和密度)，以方便模型解释和模型分辨率的研究。一项以太平洋为重点的区域研究将涉及分析从太平洋盆地内和周围的永久和临时地震台站获得的新的和现有的地震数据集。洛夫波和瑞利波基模和泛音测量将被收集。结合几个现有的走时数据集，并结合地壳厚度和板块年龄的知识，对表面波数据进行反演，以确定岩石圈和软流圈的径向和方位角各向异性结构。根据Nettles和Dziewonski（2008）的方法，将使用变分辨率参数化方法将太平洋下浅层地幔的详细模型嵌入到较粗的全球三维模型中。本研究开发的地震学模型的分析和解释将有助于更好地推断地幔的状态、组成和变形。对深部地幔弹性和密度非均质性的更严格约束，以及它们的共变，将为行星尺度动力学的地球物理模型提供信息。分辨率更高的海洋岩石圈和软流圈各向异性模型，将加强对可能的矿物结构和应变几何形状的限制，以及对浅层地幔中可能普遍存在的熔体的限制。新的地震学模型将对研究地球深部的组成、演化和动力学的广大地球科学家有用。

The goal of this project is to advance our knowledge of the large-scale elastic structure of Earth's interior using seismological imaging techniques and a broad range of seismological observations. This research will lead to an improved characterization of the anisotropic velocity structure of the mantle and will thereby help resolve the significant differences that are found between current seismological models. In particular, the research will address the existence and strength of large-scale anisotropy in the transition zone and the lower mantle, the correlation of density and elastic moduli in the deep mantle, and the scaling between shear- and compressional-velocity variations. New measurements of surface-wave overtone dispersion will be collected, which will be diagnostic of the validity of existing models that indicate strong variability in anisotropic fabric in the Pacific asthenosphere. The research will elucidate the relationship between radial and azimuthal anisotropy in the oceanic lithosphere and asthenosphere. Two linked investigations will be pursued. A global study will build on the data sets collected and analysis tools developed in the determination of the recent global model S362ANI (Kustowski et al., 2008). Project research will extend this earlier work in several ways, most importantly by (1) inclusion of normal-mode center frequencies and Q values to constrain better the global average structure, (2) incorporation of published normal-mode splitting functions to resolve transition-zone and lower-mantle velocity heterogeneity and anisotropy, and (3) formulation of the inverse problem using a flexible parameterization of covariation of model parameters (wave speeds, anisotropy, and density) to facilitate model interpretation and investigations of model resolution. A regional study focused on the Pacific will involve the analysis of new and existing seismological data sets derived from permanent and temporary seismic stations within and surrounding the Pacific Basin. Love and Rayleigh wave fundamental-mode and overtone measurements will be collected. Together with several existing travel-time data sets, and incorporating knowledge of crustal thickness and plate age, the surface-wave data will be inverted to determine the radially and azimuthally anisotropic structure of the lithosphere and asthenosphere. Following the approach of Nettles and Dziewonski (2008), a variable-resolution parameterization will be used to embed the detailed model of the shallow mantle beneath the Pacific in the coarser global 3-D model.Analysis and interpretation of the seismological models developed in this research will lead to better-supported inferences regarding the state, composition, and deformation of the Earth's mantle. Tighter constraints on elastic and density heterogeneity in the deep mantle, and their covariation, will inform geophysical models for planetary-scale dynamics. Better-resolved models of the anisotropy of the oceanic lithosphere and asthenosphere will sharpen constraints on possible mineral fabrics and strain geometries, as well as on the potentially ubiquitous presence of melts in the shallow mantle. The new seismological models will be useful for a broad range of geoscientists investigating the composition, evolution, and dynamics of the Earth's deep interior.