利用宽频带背景噪声研究大陆三维壳幔结构：以青藏高原为例

The Tibetan Plateau is the world’s largest continent-continent collision belt, and is therefore a natural laboratory for the study of continent-continent collision processes and associated deformation mechanisms. It is also one of the areas prone to the most large-earthquake in China. Investigating the detailed structures beneath the plateau, particularly the structures of the crust and upper mantle, is the key to understanding the dynamic mechanism and tectonic evolution of the plateau. Understanding detailed structures in the region also lays the foundation to studying the deformation mechanism for the whole continent and the focal mechanism of large earthquake. This project will explore the most efficient way and method of extracting long-period surface waves from seismic ambient noise. Using this newly developed method, we will process seismic ambient noise data that we collected in the Tibetan Plateau and surrounding regions from the networks including Chinse National Seismic Network (CNSN) and Global Seismographic Network (GSN). Based on the retrieved phase velocity maps at periods of 10-250 s, we aim to construct a high-resolution 3-Dimentional velocity model from the surface down to the 400 km depth across the whole Tibetan Plateau. Based on the model, we will investigate the distribution of high and low velocity anomalies in the upper mantle, which will shed light on some important questions including the geometry of the subducting Indian plate, the detailed distribution of the Tibetan lithosphere and whether the Eurasian lithosphere is subducting beneath the Tibetan Plateau. We expect the output of this project will provide important constraints on the understanding of the mechanism of the deep dynamics of the Tibetan Plateau, including both the growth pattern and shortening styles.

青藏高原是全球最大的碰撞型造山带，是研究陆陆碰撞和变形的“天然实验室”，同时也是中国大陆大地震最主要的集中地之一。深入研究青藏高原岩石圈深部结构，是认识青藏高原演化动力学机制的关键，是了解中国大陆的变形机制以及大地震的孕育机理等重要课题的基础。本项目将在大台站距背景噪声互相关的技术基础上，探究从背景噪声中提取长周期面波的最有效的处理方法。基于开发的新方法处理青藏高原及其邻区地震台站数据，结合已有的常规背景噪声研究成果，获得研究区10—250 s的相速度图像，从而构建横跨青藏高原及邻区地壳和上地幔（0—400 km）的三维横波速度模型。着重研究青藏高原岩石圈地幔高低速带的分布特征，为厘清下插印度板块的形态，青藏高原自身岩石圈分布以及是否存在欧亚板块岩石圈俯冲等重要科学问题提供可靠的地球物理模型。预期研究成果对探讨青藏高原包括隆升及缩短变形在内的深部动力学机制具有重要科学意义。

青藏高原是全球最大的碰撞型造山带，是研究陆陆碰撞和变形的“天然实验室”，同时也是中国大陆大地震最主要的集中地之一。深入研究青藏高原岩石圈深部结构，是认识青藏高原演化动力学机制的关键，是了解中国大陆的变形机制以及大地震的孕育机理等重要课题的基础。本项目取得的主要进展包括：获取了青藏高原及周边区域地壳上地幔速度结构图像；分析了青藏高原的隆升和变形机制及研究区域的动力学模型，发展了时间域相位加权叠加方法、均方根比选择叠加方法、有限频层析成像方法。研究过程中，参加了数次国内外与研究内容紧密相关的学术会议，提交会议摘要10篇；在国外专业期刊发表学术论文9篇。上述研究对认识块体相互作用的动力学机制具有重要科学意义。