Collaborative Research: Studies of Elastic and Anelastic Structure of the Earth's Mantle

该项目包括对地幔大尺度弹性和滞弹性结构的两项相互关联的调查。第一项研究涉及地球上地幔剪切衰减的三维模型的发展。该模型是由一个大的数据集的爱和瑞利面波振幅测量的周期范围为50- 250秒。 一种新的方法，它消除了多余的影响波的振幅，解决他们作为反演的一部分，使用。这种方法应用于瑞利波衰减映射的初步结果表明，它成功地隔离信号，由于振幅数据中的衰减。三维有限频率内核将被纳入反演占空间广泛的敏感性的长周期表面波在这里考虑。同时反演上地幔的滞弹性和弹性结构，既要考虑速度不均匀性对聚焦波振幅的影响，又要受到速度不均匀性对聚焦波振幅影响的制约。本研究中开发的三维衰减模型将用于解决尚未解决的基本问题，即上地幔大尺度弹性和滞弹性不均匀性的根本原因，包括温度，成分，水和部分熔融。第二项研究旨在推进地球地幔大尺度各向异性结构的制图，并建立欧亚大陆下弹性结构的区域尺度模型。这项工作扩展了现有的色散测量，互相关旅行时间，长周期波形，并同时为三维地球结构的数据反演的集合。迄今为止的工作包括反演220公里深处没有间断的上地幔的新的一维各向异性地幔，以及开发一种新技术来解释地壳结构对长周期波形的非线性影响。径向各向异性三维结构的层析成像模型的整个地幔的发展，并进行仔细的分辨率分析，以确定各向异性所需的观测。在全球模式的基础上，将采用多分辨率参数化来开发欧亚大陆下具有更高横向分辨率的模式，本项目开发的层析成像模式（弹性和滞弹性）将有助于直接解释地球地幔的组成和状态。这项研究将导致开发和分发几种数据产品，包括收集直接测量和断层扫描模型，以及使用这些产品的计算机程序。

This project consists of two linked investigations into the large-scale elastic and anelastic structure of the Earth's mantle. The first study concerns the development of a three-dimensional model of shear attenuation in the Earth's upper mantle. The model is constrained by a large data set of Love and Rayleigh surface-wave amplitude measurements in the period range 50--250 seconds. A new method, which removes extraneous effects on wave amplitude by solving for them as part of the inversion, is used. Preliminary results of this approach applied to the mapping of Rayleigh wave attenuation show that it successfully isolates the signal due to attenuation in the amplitude data. Three-dimensional finite-frequency kernels will be incorporated in the inversion to account for the spatially broad sensitivity of the long-period surface waves considered here. A simultaneous inversion for the anelastic and elastic structure of the upper mantle will both account for and be constrained by the effects on wave amplitude of focusing by velocity heterogeneity. The 3-D attenuation model developed in this study will be used to address still-unresolved but fundamental questions regarding the underlying causes of large-scale elastic and anelastic heterogeneity in the upper mantle, including temperature, composition, water, and partial melt.The second study is aimed at advancing the mapping of the large-scale anisotropic structure of the Earth's mantle, and developing a regional-scale model of the elastic structure beneath Eurasia. This work expands existing collections of dispersion measurements, cross-correlation travel times, and long-period waveforms, and inversion of the data simultaneously for three-dimensional Earth structure. Work to date has included inversion for a new one-dimensional anisotropic mantle for the upper mantle without a discontinuity at 220 km depth and the development of a new technique to account for the non-linear effects of crustal structure on long-period waveforms. Tomographic models of radially anisotropic three-dimensional structure for the whole mantle are developed, and a careful resolution analysis will be conducted to determine where anisotropy is required by the observations. Building on the global model, a multi-resolution parameterization will be employed to develop a model with greater lateral resolution beneath Eurasia.The tomographic models (elastic and anelastic) developed in this project will be useful for direct interpretation in terms of composition and state of the Earth's mantle. The research will lead to the development and distribution of several data products, including collections of direct measurements and tomographic models, as well as computer programs to make use of these products.