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

这个项目包括对地幔大尺度弹性和非弹性结构的两个相互关联的调查。第一项研究涉及地球上地幔剪切衰减的三维模型的发展。该模型受到50- 250秒期间Love和Rayleigh表面波振幅测量数据集的约束。采用了一种新的方法，通过将其作为反演的一部分求解来消除对振幅的无关影响。将该方法应用于瑞利波衰减映射的初步结果表明，它成功地隔离了由于振幅数据衰减引起的信号。三维有限频率核将被纳入反演，以考虑这里所考虑的长周期表面波的空间宽灵敏度。同时反演上地幔的非弹性和弹性结构，既要考虑到速度非均质对聚焦波幅的影响，又要受到速度非均质对聚焦波幅的影响。本研究开发的三维衰减模型将用于解决关于上地幔大规模弹性和非弹性非均质性的潜在原因的尚未解决但基本的问题，包括温度、成分、水和部分熔融。第二项研究旨在推进大尺度地幔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、相互关联旅行时间和长周期波形的收集，并同时反演三维地球结构的数据。迄今为止的工作包括反演上地幔在220公里深度无不连续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。建立了整个地幔径向各向异性三维结构层析模型，并将进行仔细的分辨率分析，以确定观测需要各向异性的地方。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。本项目开发的层析模型（弹性和非弹性）将有助于直接解释地幔的成分和状态。这项研究将导致几种数据产品的开发和分发，包括直接测量和层析模型的收集，以及利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.