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如何改变岩石组构的地震响应。地震各向异性是传播的地震波和各向异性地球材料之间的累积相互作用，其通过地震波速度的方向依赖性来表现。 由于几个因素，如3D地质几何形状和异质性，微尺度结构，地震射线路径的弯曲，由于速度梯度，现场实验，可能无法提供完整的方位角覆盖，以及观察到的各向异性作为二阶波形或走时功能，在变形的地壳岩石中解开这种效果是复杂的。 虽然地震各向异性可能源于上地壳断裂或各向同性材料的有组织的精细分层，但材料各向异性也是一个原因，至少涉及四个因素：（1）微观结构特征，包括组成矿物的空间排列、模态丰度以及晶体学和形状取向，（2）性质的固有方位角变化和使用对称类的近似，（3）不同尺度下材料性质的体表示（有效介质）;（4）宏观尺度结构的类型和内部几何形状。 宏观结构对样本尺度材料各向异性的重新取向产生了其自身的影响。 地震波将由于材料而产生一种类型的信号响应;由于结构的几何形状而重新定向的岩石包，它可以产生不同的响应。 研究人员将使用地震有效介质的概念来表示地震波传播的地球体积。 他们将采用地球体积的表示，允许有效媒体的张量表示。 这允许通过波动方程的代数张量操作，以分离结构的几何形状和岩石组成的结构。 该项目的一个主要目标是确定结构的贡献，以形成有效的媒体。每个结构都有一个几何“脉冲响应”，它将岩石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尺度岩石组构的作用如何对给定结构的有效介质做出贡献。两者联合收割机产生传播波响应的净有效介质。 他们将对常见的地壳结构几何形状及其如何修改岩石各向异性进行定量和系统的研究，并使用解析几何表面表示结构，并创建一种严格的综合方法来计算不同尺度的有效介质及其对地震波传播的综合影响。 他们还将研究如何张量形式的微观岩石织物是敏感的模态组成和统计方向的组成矿物。 该项目的成果将被设计用于辅助真实的各向异性地震数据的地震解释。该项目汇集了地震学、结构/微结构地质学和理论/计算力学方面的专门知识，以帮助建立一个定量框架，用于分析大陆地壳变形多矿物岩石中的材料各向异性和由此产生的地震各向异性。