Mapping seismic anisotropy in the mantle transition zone

绘制地幔过渡带的地震各向异性图

• 批准号: 0809464
• 负责人: Ying Zhou
• 金额: $ 18万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-15 至 2012-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0809464&HistoricalAwards=false
• 关键词: Mapping; seismic; anisotropy; mantle; transition

Intellectual Merit: The goal of this research is to advance fundamental understanding of the Earth's convection processes in the mantle through mapping seismic anisotropy in the Bullen transition zone (depth 400-1000 km). This research develops finite-frequency theory to account for wave diffraction effects in multi-mode seismic surface waves, and applies the theory to obtain high-resolution, global anisotropic 3-D structure in the Bullen transition zone. This research addresses the following important questions on mantle dynamics at a global scale including: (1) Is there significant radial anisotropy in the transition zone? How does the anisotropic structure correlate with the isotropic velocity structure? (2) Is the there any significant change in radial anisotropy across (above, within, below) the transition zone? does it support coupling or decoupling of the flow above/below the transition zone? (3) Are there any significant variations in anisotropy in the Bullen transition zone correlated with slabs and plumes? (4) Can a whole-mantle convection model explain the presence/absence and the pattern of radial anisotropy in the transition zone? How does seismic anisotropy in the Bullen transition zone fit into whole (or layered) mantle convection? This research includes the following main projects: (i) develop 3-D finite-frequency theory for multi-mode surface waves and 2-D boundary sensitivity kernels for mantle transition zone discontinuity depth perturbations, fully account for radial anisotropy in the Earth?s mantle; (ii) build a preliminary global dataset of multi-mode surface-wave measurements; and (iii) diffractional tomography using full 3-D velocity kernels and 2-D boundary kernels to obtain high-resolution global models of seismic anisotropy in the uppermost ~1000 km of the mantle. Broader impacts: The multi-mode surface-wave sensitivity kernels developed in this research can be applied to regional studies. Tomographic models will be made available on-line. The anisotropic model in the Bullen transition zone obtained in this proposed work will provide important references for mantle geodynamical modelings, and provide important seismological constraints on mantle convection hypothesis such as the transition-zone water filter model [Bercovici and Karato, 2003]. The support requested in this project will be used to educate one Ph.D graduate student.

智力优势：这项研究的目标是通过绘制布伦过渡带（深度400-1000公里）的地震各向异性图，促进对地球地幔对流过程的基本了解。本研究发展了有限频率理论来解释多模式地震面波中的波衍射效应，并应用该理论获得了布伦过渡带的高分辨率、全球各向异性的三维结构。 本文研究了全球范围内地幔动力学的以下重要问题：（1）过渡带是否存在显著的径向各向异性？各向异性结构与各向同性速度结构之间有何关系？(2)过渡区的径向各向异性是否有显著变化？它是否支持过渡区上方/下方流动的耦合或解耦？(3)在与板块和羽流相关的布伦过渡区中，各向异性是否有任何显著的变化？(4)全地幔对流模型能否解释过渡区径向各向异性的存在/不存在和模式？布伦过渡带的地震各向异性如何与整个（或层状）地幔对流相适应？本研究主要包括以下几个方面的内容：（1）发展三维有限频率多模态面波理论和二维边界灵敏度核函数，充分考虑地球径向各向异性;的地幔;（ii）建立一个初步的全球多模式面波测量数据集;（iii）使用全三维速度核和二维边界核进行衍射层析成像，以获得地幔最上层~1000公里地震各向异性的高分辨率全球模型。 更广泛的影响：本研究中开发的多模表面波敏感性内核可应用于区域研究。将在网上提供层析成像模型。本文提出的布伦过渡带各向异性模型将为地幔动力学模拟提供重要参考，并为过渡带水过滤模型等地幔对流假说提供重要的地震学约束[Bercovici and Karato，2003]。在这个项目中所要求的支持将用于教育一个博士研究生。