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学观测，增进我们对地球内部大规模弹性结构的了解。这项研究将改进地幔各向异性速度结构的特征，从而有助于解决目前地震学模型之间发现的重大差异。特别是，研究将讨论过渡带和下地幔中大尺度各向异性的存在和强度，深部地幔密度和弹性模数的相关性，以及剪切和压缩速度变化之间的标度。将收集新的面波泛音频散测量，这将诊断现有模型的有效性，这些模型表明太平洋软流层各向异性组构的强烈变异性。该研究将阐明大洋岩石圈和软流圈的径向各向异性和方位各向异性之间的关系。将进行两项相互关联的调查。一项全球研究将建立在为确定最近的全球模型S362ANI而收集的数据集和开发的分析工具的基础上(Kustowski等人，2008年)。项目研究将以几种方式扩展这一早期工作，最重要的是通过(1)包括简正波中心频率和Q值以更好地约束全球平均结构，(2)包括已发表的简正波分裂函数以解决过渡区和下地幔速度的不均一性和各向异性，以及(3)使用模型参数(波速、各向异性和密度)的灵活的协变参数来建立反问题的公式，以便于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及其周围的永久和临时地震台获得的新的和现有的地震学数据集。乐福和瑞利波的基模和泛音测量将被收集。面波数据将与几个现有的旅行时间数据集一起，并结合地壳厚度和板块年龄的知识，进行反演，以确定岩石圈和软流层的径向和方位各向异性结构。在Nettle和Dziewonski(2008)的方法之后，将使用变分辨率参数化将太平洋下浅地幔的详细模型嵌入到更粗糙的全球3-D模型中。对本研究中开发的地震学模型的分析和解释将导致关于地幔的状态、组成和变形的更好的支持的推断。对深部地幔中弹性和密度不均一性的更严格的约束，以及它们的共同变化，将为行星尺度的动力学提供地球物理模型。对大洋岩石圈和软流圈各向异性的更好解析模型将加强对可能的矿物组构和应变几何以及对浅地幔中可能普遍存在的熔体的约束。新的地震学模型将对研究地球深部的组成、演化和动力学的广泛的地球科学家有用。

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.