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

全球和板块尺度各向异性地幔结构的新约束和模型

• 批准号: 1315984
• 负责人: Goran Ekstrom
• 金额: $ 36.24万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1315984&HistoricalAwards=false
• 关键词: New; constraints; models; global; plate

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.

该项目的目标是利用地震成像技术和广泛的地震观测来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表征，从而有助于解决当前地震模型之间发现的显着差异。特别是，该研究将解决过渡带和下地幔中大尺度各向异性的存在和强度、深部地幔中密度和弹性模量的相关性，以及剪切速度和压缩速度变化之间的比例。将收集表面波泛音色散的新测量结果，这将诊断现有模型的有效性，这些模型表明太平洋软流圈中各向异性结构的强烈变化。该研究将阐明海洋岩石圈和软流圈中径向和方位各向异性之间的关系。将进行两项相关调查。全球研究将建立在确定最近全球模型 S362ANI 时收集的数据集和开发的分析工具的基础上（Kustowski 等，2008）。项目研究将以多种方式扩展这项早期工作，最重要的是（1）纳入简正模中心频率和 Q 值以更好地约束全局平均结构，（2）结合已发布的简正模分裂函数来解决转换问题区域和下地幔速度异质性和各向异性，以及（3）使用模型参数（波速、各向异性和密度）协变的灵活参数化来制定反演问题，以促进模型解释和模型分辨率研究。一项以太平洋为重点的区域研究将涉及对来自太平洋盆地及其周围的永久和临时地震台的新的和现有的地震数据集进行分析。将收集拉夫波和瑞利波基模和泛音测量结果。与几个现有的走时数据集一起，并结合地壳厚度和板块年龄的知识，表面波数据将被反演，以确定岩石圈和软流圈的径向和方位各向异性结构。遵循 Nettles 和 Dziewonski (2008) 的方法，将使用可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模型的分析和解释研究将得出关于地幔的状态、成分和变形的更有支持的推论。对深部地幔弹性和密度异质性及其协变的更严格限制将为行星尺度动力学的地球物理模型提供信息。海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结构和应变几何形状以及浅地幔中可能普遍存在的熔体的限制。新的地震学模型将有助于广泛的地球科学家研究地球深处的组成、演化和动力学。