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

• 批准号: 1722932
• 负责人: Mark Behn
• 金额: $ 12.46万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-07-15 至 2018-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1722932&HistoricalAwards=false
• 关键词: Collaborative; Research; Relating; Bulk; Composition

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 publicly 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产和其他自然资源的储藏库。此外，地壳的化学成分控制着它的物质特性（例如，强度），从而影响着地壳在地质时期的变形和演变方式。然而，虽然地球表面的地壳成分可以通过直接取样确定，但在深部的地壳成分必须通过间接方法推断，如地球物理成像。最常见的地球物理成像方法之一是利用地震波，地震波以不同的速度穿过不同的岩石类型。通过测量地震波的速度，可以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三维内部结构。在这个项目中，我们将采用地球的地震速度模型。美国大陆地壳，并将其反转以推断地壳成分。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。在过去的几十年里，通过美国国家科学基金会（NSF）的Earthscope、GeoPRISMS和Cascadia Initiative等项目，可以获得丰富的表征大陆地壳的地震数据，包括来自可控源实验的共定位纵波数据、来自接收函数的VP/VS约束以及来自环境噪声层析成像的s波数据。这些数据集为今后研究大陆地壳的性质和组成提供了基础。然而，尽管地震数据提供了丰富的信息，岩石成分和地震速度之间的定量关系仍然缺失。在这个项目中，我们将开发一套新的工具来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)建立具有代表性的地壳成分空间数据库；(2)对不同平衡P、T、H2O和fO2条件下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条件下每种相组合的VP和VS；(4)利用所得数据集建立地壳成分与地震速度之间的正演关系。这些数据将被汇编成一个公开可用的在线数据库，其他人可以使用该数据库来推导在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。为了使成分反演对社区的效用最大化，我们将开发一个基于web的Java applet，允许用户直接从他们自己的地震数据集中反演主要元素的成分。

项目成果

Inferring crustal viscosity from seismic velocity: Application to the lower crust of Southern California

• DOI: 10.1016/j.epsl.2018.04.055
• 发表时间: 2018-07
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: William J. Shinevar;M. Behn;G. Hirth;O. Jagoutz

Inferring Crustal Viscosity from Seismic Wavespeeds: Applications to the Rheologic Structure of the Himalayas

从地震波速推断地壳粘度：在喜马拉雅山流变结构中的应用

• 发表时间: 2018
• 期刊: Transactions - American Geophysical Union
• 作者: Shinevar, William J. Behn