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

大陆最古老部分的形成和演化仍然没有被完全理解，特别是为什么它们有超过200公里厚的冷而轻的根，这些根在数十亿年的破坏中幸存下来。最近对其细尺度结构的地震学研究表明，这些根内存在细尺度结构。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不同的过程先后形成的。该项目将最先进的地震成像工具应用于高质量数据集（来自USArray Earthscope地震网络），可以对美国邻近地区的深层结构进行前所未有的照明，直至大陆根部，该项目旨在详细绘制北美大陆的主要结构元素及其过渡。这些信息将成为其他地球物理学家和地球化学家进一步解决大陆形成和构造板块与深部地幔流耦合的基本问题的起点。所制订的方法也将作为在世界其他地区进行研究的基础。建议的工作将支持一名博士后和一名伯克利的研究生，以及一名高级女性地震学家的职业发展，其作为榜样的影响可能会受到赞赏。北美克拉通上地幔广泛分层的证据主要来自两类地震研究：1)各向异性层析成像，2)接收函数（RF）。两者都表明在克拉通地区存在中岩石圈边界。然而，这种MLD的性质尚不清楚，也不清楚这两种类型的数据是否看到相同的边界。本研究的目的是利用基于全非线性跨维贝叶斯反演的新方法，将北美克拉通和元古代省的高分辨率大陆尺度各向异性波形层析成像与局部层状各向异性结构的一维正演模拟相结合，以绘制落基山前带以东的主要构造，阐明岩石圈和软流层的分层性质。它将揭示MLD和岩石圈-软流圈边界的性质，岩石圈-软流圈边界一直被检测为各向异性边界，但在克拉通下的rf并不总是被检测到。本研究中产生的模型和方法将通过Earthscope/IRIS网站提供给其他研究人员。作为提议工作的一部分，我们将开发不同数据类型的概率集成的一般方法，在不同的尺度（频率）。因此，我们期望在跨维推理框架中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。

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.