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Collaborative Research: Relating Bulk Composition to Seismic Properties in Crustal Rocks

合作研究：将地壳岩石的块体成分与地震特性联系起来

基本信息

批准号：
1722935
负责人：
Oliver Jagoutz
金额：
$ 30.5万
依托单位：
Massachusetts Institute of Technology
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-07-15 至 2021-12-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1722935&HistoricalAwards=false
关键词：
Collaborative Research Relating Bulk Composition

项目摘要

The Earth's continental crust is a reservoir for minerals and other natural resources. Moreover, the chemical composition of the crust controls its material properties (e.g., strength), and thus influences the way in which the crust deforms and evolves over geologic time. However, while crustal composition at the Earth?s surface can be determined by direct sampling, at depth composition must be inferred from indirect methods such as geophysical imaging. One of the most common geophysical imaging methods employs seismic waves, which travel at different speeds through different rock types. By measuring seismic wave speeds the 3-D internal structure of the crust can be determined using an approach similar to x-ray computed tomography (CT scan) in medical studies. In this project, we will take seismic velocity models for the Earth?s continental crust and invert them to infer crustal composition. These compositional models will then be used to determine variations in crustal strength, as well as regions with different natural resource potential.In the past decades a wealth of seismic data characterizing the continental crust have become available through NSF programs such as Earthscope, GeoPRISMS, and the Cascadia Initiative?including co-located P-wave data from controlled-source experiments, VP/VS constraints from receiver functions, and S-wave data from ambient noise tomography. These datasets provide the foundation for future research on the nature and composition of the continental crust. However, despite the abundance of information provided by the seismic data, a quantitative relationship between rock composition and seismic velocity is missing. In this project we will develop a new suite of tools to relate crustal composition to seismic velocity. Our approach is divided into four steps: (1) derive a representative database for crustal composition space, (2) perform thermodynamic calculations of the equilibrating mineral assemblages for each composition at various equilibrium P,T, H2O and fO2 conditions, (3) calculate VP and VS for each phase assemblage for different in situ P,T conditions, and (4) use the resulting dataset to establish forward relationships between crustal composition and seismic velocity. These data will be compiled into a publically available online database, which can be used by others to derive relationships between major element chemistry and seismic velocity under a specified range of crustal conditions. The project will support MIT/WHOI Joint Program student William Shinevar. To maximize the utility of the compositional inversion to the community we will develop a web-based Java applet to allow users to directly invert major element compositions from their own seismic datasets.

地球的大陆地壳是矿物和其他自然资源的储藏库。此外，地壳的化学成分控制其材料特性（例如强度），从而影响地壳在地质时期变形和演化的方式。然而，虽然地球表面的地壳成分可以通过直接采样确定，但深度成分必须通过地球物理成像等间接方法推断。最常见的地球物理成像方法之一采用地震波，地震波以不同的速度穿过不同的岩石类型。通过测量地震波速度，可以使用类似于医学研究中的 X 射线计算机断层扫描（CT 扫描）的方法来确定地壳的 3D 内部结构。在这个项目中，我们将采用地球大陆地壳的地震速度模型并对其进行反演以推断地壳成分。然后，这些成分模型将用于确定地壳强度的变化以及具有不同自然资源潜力的区域。在过去的几十年中，通过 Earthscope、GeoPRISMS 和 Cascadia Initiative 等 NSF 计划，我们可以获得大量表征大陆地壳的地震数据，包括来自受控源实验的同位 P 波数据、来自接收器函数的 VP/VS 约束以及来自环境噪声断层扫描。这些数据集为未来研究大陆地壳的性质和组成奠定了基础。然而，尽管地震数据提供了丰富的信息，但缺乏岩石成分和地震速度之间的定量关系。在这个项目中，我们将开发一套新的工具，将地壳成分与地震速度联系起来。我们的方法分为四个步骤：(1) 导出地壳成分空间的代表性数据库，(2) 在不同的平衡 P、T、H2O 和 fO2 条件下对每种成分的平衡矿物组合进行热力学计算，(3) 计算不同原位 P、T 条件下每个相组合的 VP 和 VS，以及 (4) 使用生成的数据集建立地壳之间的正向关系成分和地震速度。这些数据将被编译成一个公开的在线数据库，其他人可以使用该数据库来推导特定地壳条件范围内主要元素化学和地震速度之间的关系。该项目将支持麻省理工学院/WHOI 联合项目学生 William Shinevar。为了最大限度地提高成分反演对社区的效用，我们将开发一个基于 Web 的 Java 小程序，以允许用户直接从自己的地震数据集中反演主要元素成分。