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

该项目包括对地幔的大范围弹性和滞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中剪切衰减的三维模型的发展。该模型在50-250秒的周期范围内受到乐福和瑞利面波振幅测量的大量数据集的限制。采用了一种新的方法，即通过求解波幅作为反演的一部分来消除对波幅的外部影响。将该方法应用于瑞雷波衰减成图的初步结果表明，该方法成功地分离了幅度数据中衰减引起的信号。三维有限频率核将被加入到反演中，以解释这里所考虑的长周期面波的空间广泛的敏感性。同时反演上地幔的滞弹性和弹性结构，既能解释速度不均匀对聚焦波幅的影响，又能受其制约。这项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滞弹性不均匀的根本原因的尚未解决的基本问题，包括温度、成分、水和部分熔融。第二项研究旨在推进地幔大尺度各向异性结构的绘制，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、互相关旅行时和长周期波形的集合，并同时对三维地球结构的数据进行了反演。迄今的工作包括对220公里深度没有间断的上地幔进行新的一维各向异性地幔的反演，并开发了一种新的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的层析模型，并将进行仔细的分辨率分析，以确定观测需要各向异性的位置。在全球模式的基础上，将使用多分辨率参数化来开发欧亚大陆下更高横向分辨率的模式。在该项目中开发的层析模式(弹性和滞弹性)将有助于直接解释地幔的组成和状态。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成像模型，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.