Anisotropic Layering in the North American Upper Mantle Using a Combination of Seismological Approaches

结合地震学方法研究北美上地幔的各向异性分层

• 批准号: 1460205
• 负责人: Barbara Romanowicz
• 金额: $ 35.43万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1460205&HistoricalAwards=false
• 关键词: Anisotropic; Layering; North; American; Upper

The formation and evolution of the oldest parts of continents is still not fully understood, and in particular why they have cold but light roots in excess of 200 km thickness that have survived destruction over billions of years. Recent seismological studies of their fine scale structure has revealed the presence of fine scale structure within these roots. There is an indication that the shallower half has a distinct structure from the deeper part which suggests that they may have formed successively, through somewhat different processes. Applying state-of-the-art tools of seismic imaging to a high quality dataset (from the USArray seismic network of Earthscope) that allows unprecedented illumination of the deep structure of the conterminous United States, down to and beyond the continental root, this project aims at detailed mapping of the major structural elements and their transitions across the north American continent. This information will serve as a starting point for other geophysicists and geochemists to further address the fundamental questions of continental formation and coupling of tectonic plates with deep mantle flow. The methodologies developed will also serve as basis for studies in other parts of the world. The proposed work will support the career development of a post-doc and a graduate student at Berkeley, and a senior female seismologist, whose influence as role model may be appreciated. Evidence for widespread layering in the cratonic upper mantle in north America comes primarily from two types of seismic studies: 1) anisotropic tomography, and 2) receiver functions (RF). Both indicate the presence of a mid-lithospheric boundary (MLD) in cratonic areas. However, the nature of this MLD is not known nor is it clear whether the two types of data see the same boundary. The goal of this proposal is to combine high resolution continental scale anisotropic waveform tomography in the craton and proterozoic provinces of north America (NA), with 1D forward modeling of local layered anisotropic structure using a novel approach based on fully non-linear trans-dimensional Bayesian inversion, in order to map major structural and clarify the nature of lithosphere and asthenosphere layering east of the Rocky Mountain Front. It will shed light on the nature of the MLD and of the lithosphere-asthenosphere boundary, which is consistently detected as an anisotropic boundary, but is not consistently detected by RFs under the craton. The models and methodologies produced in this study will be made available to other investigators through the Earthscope/IRIS websites. As part of the proposed work, we will develop general methodologies for probabilistic integration of different data types, at different scales (frequencies). We thus expect the theoretical framework and algorithms developed here in the framework of trans-dimensional inference can be extended to include other types of data and will be useful to other researchers in seismology and Earth sciences.

大陆最古老部分的形成和演化仍然不完全清楚，特别是为什么它们有超过200公里厚的冷而轻的根部，这些根部在数十亿年的破坏中幸存下来。最近对其细微尺度结构的地震学研究表明，这些根部存在细微尺度结构。有迹象表明，较浅的一半与较深的部分具有不同的结构，这表明它们可能是通过一些不同的过程连续形成的。将最先进的地震成像工具应用于一个高质量的数据集(来自美国地球望远镜阵列地震网络)，可以前所未有地照亮毗邻的美国的深层结构，直到大陆根部和大陆根部之外，该项目旨在详细绘制北美大陆主要结构元素及其过渡的地图。这些信息将作为其他地球物理学家和地球化学家进一步研究大陆形成和构造板块与深部地幔流动耦合的基本问题的起点。制定的方法也将作为在世界其他地区进行研究的基础。拟议的工作将支持伯克利一名博士后和一名研究生的职业发展，以及一名高级女性地震学家的职业发展，她们作为榜样的影响力可能会受到赞赏。北美克拉通上地幔广泛分层的证据主要来自两种类型的地震研究：1)各向异性层析成像；2)接收函数(RF)。两者都表明克拉通地区存在中岩石圈边界(MLD)。然而，这一MLD的性质尚不清楚，也不清楚这两种类型的数据是否具有相同的边界。这一提议的目标是将北美克拉通和元古界的高分辨率大陆尺度各向异性波形层析成像与使用基于完全非线性跨维贝叶斯反演的新方法对局部层状各向异性结构进行一维正演模拟相结合，以绘制主要构造图，并澄清落基山脉前缘以东的岩石圈和软流圈分层的性质。它将揭示MLD和岩石圈-软流圈边界的性质，该边界一直被检测为各向异性边界，但克拉通下的RFS并不一致地检测到。这项研究中产生的模型和方法将通过地球望远镜/IRIS网站提供给其他调查人员。作为拟议工作的一部分，我们将制定在不同尺度(频率)对不同数据类型进行概率综合的一般方法。因此，我们期待在跨维推理框架下开发的理论框架和算法可以扩展到包括其他类型的数据，并将对地震学和地球科学的其他研究人员有用。