Collaborative Research: Joint inversion of crust and upper mantle structure in central and eastern Tibetan plateau and its margins

合作研究：青藏高原中东部及其边缘地壳上地幔结构联合反演

• 批准号: 0838188
• 负责人: Xiaodong Song
• 金额: $ 18.49万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-06-15 至 2012-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838188&HistoricalAwards=false
• 关键词: Collaborative; Research; Joint; inversion; crust

This award is funded under the American Recovery and Reinvestment Actof 2009 (Public Law 111-5).(a) Broader significance of the projectHow does the Himalaya rise up to today's height? How is the Tibetan Plateau (TP) formed? How is the crust of plateau deforming to produce great earthquakes, such as the one we witnessed on May 12, 2008 in Wenchuan, China, which killed over 70,000 people? We know that the plateau is generated by the collision between India and Eurasia, which started about 60 million years ago. However, important details are missing. A major obstacle is our limited ability to "see" through 3D structure below the surface, making it difficult to relate surface geological structures and deformation to the underlying forces. The purpose of this project is to use a variety of seismic imaging techniques and unprecedented amount of seismic data that we will collect from global databases as well as those inside China to image the subsurface structure of central and eastern TP and its margins. These images will provide critical information to test key hypotheses on plateau formation and deformation.Our research has broad implications for fundamental questions about the mechanisms and processes of mountain building, plateau formation, continental deformation, and seismic hazards in the region. The project will be an excellent opportunity for international scientific collaboration with China. It will support one graduate student from U. Illinois and one from Saint Louis U. We will also engage undergraduates for seismology training and seismic data processing skills.(b) Technical description of the project.A great variety of models have been proposed to explain the uplifting, formation, and deformation of the Tibetan Plateau. A major problem is the limited resolution of seismic imaging of the sub-surface 3D structure, making it difficult to relate seismic parameters to geological structures and processes. We propose to use joint-inversion methods involving multiple datasets to improve resolution of both P and S structures of the lithosphere in the central and eastern TP. We propose to jointly interpret P travel times, receiver functions, and surface-wave dispersion measurements from both ambient noise correlation and traditional earthquake-based method to derive 3D models of P and S velocities and anisotropies. In seismic inversion, model parameters often trade off with each other. To improve resolution and to resolve the ambiguity, a combination of different data sets that have sensitivities to different parameters is required or a priori constraints have to be imposed. The abundance of data now accessible makes our joint inversions feasible.We are particularly interested in the crustal channel flow model, which suggests that mid-lower crust flows in response to topographic loading and the deformation of the upper crust is decoupled from the underlying mantle. We select central and eastern Tibet based on the need for sufficient data coverage and on our desire to study a sufficient large area to avoid possible bias from local heterogeneity and to compare the convergence regime (central Tibet) with the extrusion regime (E. Tibet).The key questions we seek to address include:(1) mid-crust channel flow: Is there evidence for widespread mid-crust channel flow? Where in the plateau does it occur?(2) directions of crustal channel flow: What are the directions of the channel flow? How does the direction change from central Tibet to eastern Tibet and to the southeastern and northeastern margins?(3) coupling or decoupling of crustal and mantle deformation: How does deformation change with depth? Is the upper crust deformation decoupled from the deformation in the mantle lithosphere?(4) changes of structure and deformation from central Tibet to eastern Tibet: What is the extent of the India lithosphere underthrusting beneath the TP? What are the differences and connections in structures and deformation at depth among different regions? What controls do the major structures at the margins exert on the crustal and mantle deformation?

该奖项是根据2009年《美国复苏与再投资法》（公法111-5）资助的。藏族高原（TP）是如何形成的？高原的外壳如何产生巨大的地震，例如我们在2008年5月12日在中国韦库恩（Wenchuan）目睹的地震造成的地震，造成超过70,000人丧生？我们知道高原是由印度和欧亚大陆之间的碰撞产生的，该碰撞始于大约6000万年前。但是，缺少重要的细节。一个主要的障碍是我们有限的能力通过表面下方的3D结构“看到”，因此很难将表面地质结构和变形与基础力相关联。该项目的目的是使用各种地震成像技术和前所未有的地震数据，我们将从全球数据库以及中国内部的数据库中收集，以形象中央和东部TP及其边缘的地下结构。这些图像将提供关键的信息，以检验有关高原形成和变形的关键假设。我们的研究对该地区的基本问题和过程具有广泛的意义。该项目将是与中国国际科学合作的绝佳机会。它将支持来自美国伊利诺伊州的一名研究生，以及来自圣路易斯U的一名研究生，我们还将吸引本科生进行地震学培训和地震数据处理技能。（b）对项目的技术描述。已经提出了各种各样的模型来解释藏族高原的振奋，形成和变形。一个主要问题是地下3D结构的地震成像的有限分辨率，因此很难将地震参数与地质结构和过程联系起来。我们建议使用涉及多个数据集的联合发生方法来改善中央和东部TP中岩石圈的P和S结构的分辨率。我们建议从环境噪声相关和基于传统地震的方法中共同解释P旅行时间，接收器函数和表面波色散测量，以得出P和S速度和各向异性的3D模型。 在地震反演中，模型参数通常相互交易。为了改善分辨率并解决歧义，需要对不同参数具有敏感性的不同数据集的组合，或者必须施加先验约束。现在，可访问的数据丰度使我们的联合反转可行。我们对地壳通道流模型特别感兴趣，这表明中慢地壳流动响应地形负载响应于地形负载，并且上皮的变形与下面的地幔脱钩。 我们根据需要进行足够的数据覆盖范围以及我们研究足够大面积以避免局部异质性可能偏见并比较融合制度（中央西藏）与挤压方案（E.藏族）的愿望（E. tibet）的愿望（E. tibet）。 （2）地壳通道流的方向在哪里发生：通道流的方向是什么？方向如何从西藏中部到东部以及东南边缘和东北边缘？（3）地壳和地幔变形的耦合或解耦：变形如何随深度而变化？上皮变形是否与地幔岩石圈的变形脱钩？（4）结构和从西藏中部到东部西藏的变化的变化：印度岩石圈在TP下的污染程度是多少？不同区域之间深度的结构和变形的差异和连接是什么？边缘在地壳和地幔变形上施加的主要结构有哪些控制？