Collaborative Research: Multiscale analysis of geological structures that influence crustal seismic anisotropy

合作研究：影响地壳地震各向异性的地质结构的多尺度分析

• 批准号: 1015599
• 负责人: David Okaya
• 金额: $ 16.06万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-15 至 2013-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1015599&HistoricalAwards=false
• 关键词: Collaborative; Research; Multiscale; analysis; geological

This project is a study of crustal material anisotropy with a focus on macroscale structural geometries and how they will modify the seismic response of rock fabrics. Seismic anisotropy is the cumulative interplay between propagating seismic waves and anisotropic earth material that manifests itself through the directional dependence of seismic wave speeds. Unraveling this effect in deformed crustal terranes is complex due to several factors, such as 3D geological geometry and heterogeneity, microscale fabric, bending of seismic raypaths due to velocity gradients, field experiments that may not offer full azimuthal coverage, and the observation of anisotropy as second-order waveform or traveltime features. While seismic anisotropy can originate from upper crustal fractures or by organized fine-scale layering of isotropic material, material anisotropy is also a cause and involves at least four factors: (1) microstructural characteristics including spatial arrangement, modal abundances, and crystallographic and shape orientations of constituent minerals, (2) inherent azimuthal variation of properties and approximation using symmetry classes, (3) bulk representation (effective media) of material properties at different scales, and (4) the types and internal geometries of macroscale structures. The reorientation of sample-scale material anisotropy by macroscale structures imparts its own effect. A seismic wave will produce one type of signal response due to material; it can produce a different response due to a package of rocks that are reoriented due to the geometry of a structure. The researchers will use the concept of seismic effective media to represent earth volumes through which seismic waves travel. They will employ a representation of earth volumes that allow for a tensorial representation of effective media. This allows via the wave equation an algebraic tensor manipulation to separate the structural geometry and the rocks composing the structure. A primary goal of the project is to define the contributions of structure to form effective media. Each structure has a geometrical "impulse response" which will modify a rock texture into an effective medium representation of the structure. A second goal of the project is to understand how the role of microscale rock fabrics contribute towards the effective media for given structures. Both combine to produce the net effective medium that a propagating wave responds to. They will conduct a quantitative and systematic study of common crustal structural geometries and how they modify rock anisotropy, and represent structures using analytical geometry surfaces and create a rigorous and integrated methodology to calculate effective media at different scales and their combined effects on seismic wave propagation. They will also examine how the tensorial form of microscale rock fabrics are sensitive to the modal compositions and statistical orientations of constituent minerals. Results of this project will be designed to aid the seismic interpretation of real anisotropic seismic data. This project brings together expertise in seismology, structural/microstructural geology and theoretical/computational mechanics to help develop a quantitative framework for the analysis of material anisotropy and resulting seismic anisotropy in deformed polymineralic rocks of the continental crust.

该项目是对地壳材料各向异性的研究，重点是宏观结构几何形状以及它们将如何修改岩石织物的地震反应。地震各向异性是传播地震波和各向异性地球物质之间的累积相互作用，它们通过地震波速度的方向依赖性表现出来。 由于几个因素，例如3D地质几何形状和异质性，显微镜织物，由于速度梯度引起的地震射线Pathers的弯曲，现场实验可能无法提供全部Azimuthal的覆盖范围，以及对Anisotropy的二阶波动或第二阶段的观察。 While seismic anisotropy can originate from upper crustal fractures or by organized fine-scale layering of isotropic material, material anisotropy is also a cause and involves at least four factors: (1) microstructural characteristics including spatial arrangement, modal abundances, and crystallographic and shape orientations of constituent minerals, (2) inherent azimuthal variation of properties and approximation using对称类别，（3）在不同尺度上的材料特性的体积表示（有效培养基），以及（4）宏观结构的类型和内部几何形状。 宏观结构对样品级材料各向异性的重新定位赋予其自身效果。 地震波将由于物质引起的一种类型的信号响应。由于结构的几何形状，由于岩石的重新定位，因此可以产生不同的响应。 研究人员将使用地震有效培养基的概念来表示地震波传播的地球量。 他们将采用地球量的代表，允许有效培养基的张力表示。 这允许通过波方程来进行代数张量操作，以分离组成结构的结构几何形状和岩石。 该项目的主要目标是定义结构形成有效媒体的贡献。每个结构都有一个几何“脉冲响应”，它将将岩石的纹理修改为结构的有效介质表示。 该项目的第二个目标是了解微观岩石织物的作用如何为给定结构的有效媒体做出贡献。两者结合以产生传播波响应的净有效培养基。 他们将对常见的地壳结构几何形状以及它们如何修饰岩石各向异性进行定量和系统的研究，并使用分析几何表面表示结构，并创建一种严格而综合的方法，以在不同的尺度上计算有效的培养基及其对震荡波传播的综合作用。 他们还将研究微观岩石织物的张力形式如何敏感组成矿物的模态组成和统计取向。 该项目的结果将旨在帮助对实际各向异性地震数据的地震解释。该项目汇集了地震学，结构/微观结构地质学和理论/计算力学方面的专业知识，以帮助开发一个分析材料各向异性分析的定量框架，并在大陆壳的变形多层次岩石中产生地震性各向异性。