Collaborative Research: Imaging the Upper Mantle Beneath the Western Tibetan Plateau

西藏是了解大陆碰撞大尺度动力学的关键，但西藏地下地幔的很大一部分仅用相对低分辨率的技术进行了探测。我们所知道的足以说明，青藏高原西部广大地区的平均地震波速度异常之高，但我们缺乏足够的信息，无法区分造成这些异常的大量可能情况，以及它们在造山动力学中可能发挥的作用。例如，这些高波速（即相对较冷）的块体是西藏岩石圈固有的，下沉到高原之下并将邻近的地幔物质拉入其中，还是它们代表了俯冲的印度板块的前缘，从侧面提供了一个遥远的推力？该项目的主要目标是绘制这些高波质量在西藏地下上地幔的分布图，以便区分这些相互竞争的假设。该测绘将通过分析地震数据集来完成，该数据集是通过在西部高原部署多阶段准线性宽带站阵列收集的，该数据集结合了长期（2-3年）低频到达的记录和短期（1年）阶段记录高频到达的记录。传统的和最近发展的技术的结合，主要基于到达时间断层扫描和接收函数分析的变化，将用于处理。该项目将由3名pi和2名或以上的美国研究生和本科生与大量来自中国的同事（科学家、技术人员和学生）合作进行，这些同事主要来自北京的中国地震局，也来自拉萨的西藏地震局。此外，海得拉巴国家地球物理研究所的同事们将通过在印度进行同步部署来扩大我们的覆盖范围。

Tibet is key to understanding the large-scale dynamics of continental collisions, yet a substantial part of the mantle beneath Tibet has been probed only with relatively low-resolution techniques. We know enough to say that on average seismic wavespeeds in the vast western part of the plateau are unusually high, but we lack sufficient information to discriminate among a large number of plausible scenarios for what is causing these anomalies and what role they might play in the dynamics of mountain building. For example, are these high wavespeed (i.e., relatively cold) masses indigenous to the Tibetan lithosphere, sinking beneath the plateau and drawing adjacent mantle material into it, or do they represent the leading edge a subducting Indian plate that provides a distant push from the side? The primary objective of this project is to map the distribution of these high wavespeed masses in the upper mantle beneath Tibet in order to distinguish among these competing hypotheses. This mapping will be done by analyzing a seismological dataset gathered by deploying a multi-stage, quasi-linear array of broadband stations across the western plateau that combines long period (2-3 year) recording of lower frequency arrivals with shorter period (1 year) staged recording of higher frequency arrivals. A combination of traditional and recently developed techniques, based mostly on variations of arrival time tomography and receiver function analysis, will be used in the processing. This project will be carried out by 3 PIs and 2 or more graduate and undergraduate students in the US in collaboration with a substantial number of coworkers (scientists, technicians, students) from China, mostly from the Chinese Seismology Bureau in Beijing but also from the Tibetan Bureau of Seismology in Lhasa. Additionally, colleagues from the National Geophysical Research Institute in Hyderabad will extend our coverage across the border by carrying out a simultaneous deployment in India.