Integrated Analytical-Computational Analysis of Microstructural Influences on Seismic Anisotropy

地球弹性各向异性的大小、方向和空间分布地幔对流、幔壳耦合和板块构造作用等引起的热、力学和运动学参数梯度的变化，为地壳和地幔的演化提供了重要的信息。有关地震信号的变形制度需要的弹性签名（体刚度）的不同的微观结构，表征特定的变形环境的知识，但微观结构的不均匀性对体刚度的影响还没有得到全面评估。本项目的目标是：（1）扩大一个初步的方法，以确定整体刚度的岩石使用集成的分析（电子背散射衍射）和计算（渐近膨胀均匀化）方法，充分考虑样品中不同矿物之间的颗粒尺度弹性相互作用;（2）应用该综合框架研究了几种常见地壳微结构对弹性各向异性的影响;（3）将随时间变化的微结构模拟与体刚度计算相结合，以研究应变和过程相关的微结构演化对地幔岩石弹性各向异性的影响;以及（4）传播用于从电子背散射衍射数据计算体刚度和创建可用于灵敏度分析以及其他应用的合成（计算机生成）微结构的开放源代码软件。由于常用的方法，如Voigt，Reuss和Voigt-Reuss-Hill平均值，用于计算块体岩石的刚度，并不考虑组成矿物之间的弹性相互作用，它们与用渐近展开均匀化方法得到的刚度有明显的、非系统的差异。这些目标是重要的，因为这些结果将大大提高对地壳中地震各向异性性质的理解，它是由结构复杂的低对称矿物为主的岩石组成。执行这些计算的传统方法不容易包含这些效应。该项目将为各向异性材料开发一种优雅，易于实施的替代方法。该项目产生的科学成果和计算工具将在全球范围内应用于许多固体地球和工程学科。本项目开发的开源代码将通过现有的开源ELLE平台提供。为使用该软件的地球科学和机械工程课程开发的课堂练习将提供给社区，可能是通过卡尔顿学院的科学教育资源中心网站。

The magnitudes, orientations and spatial distributions of elastic anisotropy in Earth?s crust and mantle carry valuable information about gradients in thermal, mechanical and kinematic parameters arising from mantle convection, mantle-crust coupling and tectonic plate interactions. Relating seismic signals to deformation regimes requires knowledge of the elastic signatures (bulk stiffnesses) of different microstructures that characterize specific deformation environments, but the influence of microstructural heterogeneity on bulk stiffness has not been comprehensively evaluated. The objectives of this project are to: (1) scale up a preliminary method to determine the bulk stiffness of rocks using integrated analytical (electron backscatter diffraction) and computational (asymptotic expansion homogenization) approaches that fully account for the grain-scale elastic interactions among the different minerals in the sample; (2) apply this integrated framework to investigate the effect on elastic anisotropy of several common crustal microstructures; (3) integrate time-dependent microstructure modeling with bulk stiffness calculations to investigate the effects of strain- and process-dependent microstructure evolution on elastic anisotropy in mantle rocks; and (4) disseminate open-source software for the calculation of bulk stiffnesses from electron backscatter diffraction data and creation of synthetic (computer generated) microstructures that can be used in sensitivity analyses among other applications. Because commonly used methods, such as the Voigt, Reuss and Voigt-Reuss-Hill averages, for calculating bulk rock stiffnesses do not account for elastic interactions among the constituent minerals, they exhibit marked, non-systematic differences from stiffnesses obtained using asymptotic expansion homogenization.These objectives are important because the results would substantially improve understanding of the nature of seismic anisotropy in the Earth's crust, which is composed of rocks dominated by low symmetry minerals with complex structures. Traditional methods for performing these calculations do not easily incorporate these effects. This project will develop an elegant, easily-implemented alternative method for anisotropic materials. The scientific results and computational tools that result from this project will have global application across a number of solid Earth and engineering disciplines. Open-source codes developed in this project will made available through existing open-source ELLE platform. Classroom exercises developed for Earth Science and Mechanical Engineering courses that employ this software will be make available to the community, probably through the Science Education Resource Center website at Carleton College.