Integrated Analytical-Computational Analysis of Microstructural Influences on Seismic Anisotropy

S地壳和地幔弹性各向异性的大小、方向和空间分布提供了有关地幔对流、壳-幔耦合和构造板块相互作用引起的热、力学和运动学参数梯度的有价值的信息。将地震信号与变形状态联系起来，需要了解表征特定变形环境的不同微观结构的弹性特征(整体刚度)，但微观结构的异质性对整体刚度的影响尚未得到全面评估。该项目的目标是：(1)利用综合分析(电子背散射衍射)和计算(渐近膨胀均一化)方法，扩大确定岩石整体硬度的初步方法；(2)应用这个综合框架，研究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积刚度计算相结合，研究依赖应变和过程的微结构演化对地幔岩石弹性各向异性的影响；以及(4)传播开源软件，用于根据电子背向散射衍射数据计算整体硬度，并创建可用于灵敏度分析等应用的合成(计算机生成)微结构。由于常用的计算块状岩石硬度的方法，如Voigt、Reuss和Voigt-Reuss-Hill平均，没有考虑组成矿物之间的弹性相互作用，它们与使用渐近膨胀均一化获得的硬度显示出显著的非系统性差异。这些目标是重要的，因为这些结果将极大地提高对地壳地震各向异性本质的理解，地壳由具有复杂结构的低对称性矿物主导的岩石组成。进行这些计算的传统方法不容易包含这些影响。该项目将为各向异性材料开发一种优雅、易于实现的替代方法。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固体地球和工程学科。在这个项目中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向社区提供，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.