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

西藏是理解大陆碰撞的大规模动力学的关键，然而西藏下面的地幔的很大一部分只用相对低分辨率的技术进行了探测。我们知道，平均而言，高原西部广大地区的地震波速异常高，但我们缺乏足够的信息来区分大量看似合理的情景，即是什么导致了这些异常，以及它们可能在造山动力中扮演什么角色。例如，这些高波速(即相对较冷的)块体是西藏岩石圈的本土物质，沉入高原下方并将邻近的地幔物质拉入其中，还是它们代表了前缘的俯冲印度板块，提供了从侧面提供远距离推动的作用？这个项目的主要目标是绘制这些高波速物质在西藏下地幔中的分布图，以便区分这些相互竞争的假说。这一映射将通过分析通过在西部高原部署多阶段准线性宽带站阵列而收集的地震学数据集来完成，该宽带站阵列将低频率到达的长周期(2-3年)记录与高频率到达的短周期(1年)分段记录相结合。在处理中将使用传统技术和最近开发的技术的组合，这些技术主要基于到达时间层析成像和接收器函数分析的变化。该项目将由3名PI和2名或更多在美国的研究生和本科生与中国的大量同事(科学家、技术人员、学生)合作实施，这些同事大多来自北京的中国地震局，但也来自拉萨的西藏地震局。此外，来自海得拉巴国家地球物理研究所的同事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.