Crustal Anisotropy and Mantle Stratigraphy in the Tibetan Plateau and Central Andes

地球上最大的山脉和最高的高原是在大陆碰撞时建造的。地震转换相(接收函数)被用来研究大陆碰撞中的两个关键问题：下地壳是否流动在高高原之下，以及大陆地幔是否俯冲到山带之下？如果像一些模拟预测的那样，地壳流动发生在一个相对较薄的水道中，它将形成一种强大的构造或矿物组构，可以通过地震各向异性来识别。与仅提供震源和接收器之间的总体各向异性信息的横波分裂研究不同，转换相的方位变化可以约束地壳内各向异性参数。以前的研究一般发现地壳各向异性为5%，但最近使用接收函数方法在新西兰和中央安第斯山脉发现了地壳内的高度各向异性(10%)层。这项新技术正在应用于地球上海拔最高的青藏高原上记录的接收函数，以寻找大规模地壳流动的证据。大陆稳定内部之下的上地幔在大范围内分层。有些层的边界是区域性观测的，地震学家将其命名为“H”、“X”和“L”。大陆上地幔分层的起源目前还知之甚少。在一些地方，分层具有明显的倾斜性。接收器函数已被用于成像现代俯冲带，以及识别古代克拉通下方上地幔的倾斜层。克拉通之下的这些层中的一些似乎具有各向异性，并可能识别残留的大陆俯冲带。即使层结的起源未知，它也可以被用作追踪大陆碰撞带下撞击的强板块俯冲或破坏的“示踪剂”，例如，追踪喜马拉雅山和西藏下面的印度板块。这个项目的主要目标是绘制青藏高原的地壳各向异性和上地幔分层图，并利用结果来提高我们对高原建造高度的理解。这项研究将继续发展接收函数技术在地震各向异性和地幔地层学研究中的应用，并为两位年轻科学家的技术教育做出贡献。

The largest mountains and highest plateaus on Earth are built when continents collide. Seismic converted phases (receiver functions) are used to investigate two key questions in continental collisions: does the lower crust flow beneath high plateaus, and does continental mantle subduct beneath mountain belts? If crustal flow occurs in a relatively thin channel, as some modeling predicts, it would develop a strong structural or mineral fabric that may be identified by seismic anisotropy. Unlike shear-wave splitting studies that provide only bulk anisotropy information between the source and receiver, azimuthal variations of converted phases can constrain anisotropy parameters for layers within the crust. Previous studies have generally found crustal anisotropies 5%, but highly anisotropic (10%) layers within the crust have recently been identified in New Zealand and the Central Andes using the receiver function method. This new technique is being applied to receiver functions recorded across the highest elevations on Earth, the Tibetan Plateau, in order to search for evidence of large-scale crustal flow.The upper mantle beneath the stable interiors of continents is layered on a large scale. Some layer boundaries are observed regionally and denoted by seismologists as "H", "X", and "L". The origin of the stratification of the continental upper mantle is still poorly understood. In some locations the layering has significant dip. Receiver functions have been used to image modern subductions zones as well as identify dipping layers in the upper mantle beneath ancient cratons. Some of these layers beneath cratons appear to have anisotropic properties and may identify relict continental subduction zones. Even if the origin of the stratification is unknown, it can be used as a "tracer" to follow the subduction or destruction of an impinging strong plate beneath a continental collision zone, for example, to track the Indian plate beneath the Himalayas and Tibet.The primary goal of this project is to map out crustal anisotropy and upper mantle layering across the Tibetan Plateau, and use the results to improve our understanding of how high plateaus are built. This research will continue the development of the receiver function technique in the study of seismic anisotropy and mantle stratigraphy, and contribute to the technical education of two young scientists.