青藏高原北部及邻区壳幔结构特征与深部过程研究

The Northern Tibet and its surrounding areas are the key regions for understanding the deep process during the convergence between Indian-Asian continents and the mechanism of the plateau's growth. However, because of the hardly traffic conditions and the senstive natural environments, only few passive- and/or active-souce seismic explorations were achieved at there, by overcoming a great deal of difficulties. Therefore, for the investigation in such hardly accessable regions, it is crucial to integrate some indirected seismological methods based on the available seismic data from different observations effectively. In this study, we will use almost all the available data recorded by the stations of the Digital Seismic Networks and the Portable Seismic Arrays deployed in Tibet by different institutions or projects, and will integrate the traditional Surface Wave Tomography, the Ambient Noise Tomography, and the Analysis and Imaging of Receiver Functions to reconstruct the crustal and upper-mantle structure beneath the Northern Tibet and its surrounding areas. Some external characteristics and its intrinsic mechanism, including the lower crustal double discontinuities of the Lhasa Block, the lower crustal and upper mantle velocities of the Qiangtang Block, and the crustal and upper mantle structure and deformation of the central segment of the Altyn Tagh fault zone, will be focused to investigate, and then, the deep process and the interaction between the crust and mantle during the Indian-Asian continental collision will be discussed constrained by the seismological evidences achieved.

青藏高原北部及邻区是开展印度-亚洲大陆汇聚的深部过程及高原生长机制研究的关键地区。长期以来，受自然条件、人文环境等客观因素制约，系统的、直接的深部地震探测工作难以在该区得到大规模、有效地组织与开展。因此，基于现有的各类地震观测数据，集成发挥无需进入工作地区、高分辨率的、间接地震学探测方法的优势，开展该区壳幔结构特征及动力学研究具有重要的理论和实际意义。本项研究拟在整合利用青藏高原现有固定地震台网、临时流动地震台阵资料的基础上，联合传统面波成像、环境噪声成像和接收函数分析与成像等地震学方法，重建青藏高原北部及邻区的地壳上地幔结构；通过聚焦研究拉萨地块下地壳双间断面、羌塘地块下地壳与上地幔顶部速度、阿尔金断裂系中段壳幔结构与形变特征等关键科学问题，为探讨印度-亚洲大陆碰撞的深部过程及壳幔相互作用提供可靠的地震学约束。

长期以来，青藏高原北部和西构造节等关键地带受自然条件、人文环境等客观因素制约，系统的、直接的深部探测工作难以得到大规模、有效地组织开展。基于现有的地震观测数据，集成发挥无需进入工作地区、高分辨率地震学探测方法的优势，系统开展壳幔结构特征及动力学研究具有重要的理论和实际意义。依托本项目支持，组织开展了地壳厚度-波速比-Moho面倾角同步求取新方法研究；关键地段二维剖面各向异性分析、接收函数/环境噪声成像研究；青藏高原北部及邻区、西构造节面波层析成像研究，在以下方面取得了重要进展： .（1）在拉萨块体中部开展密集地震台阵探测，联合利用SKS到时和分裂时差，检测印度岩石圈板片的俯冲距离和俯冲角度，提出了印度岩石圈板片撕裂和断离的动力学模型。.（2）利用环境噪声成像方法，获得了高原北部和塔里木盆地地壳上地幔高分辨率三维速度结构，揭示出南北向裂谷系地壳结构的条带性、塔里木高速下地壳向青藏高原中地壳低速层楔入、塔西南中下地壳大范围高速异常等特征，为南北向裂谷系形成机制、塔里木盆地与高原接触关系、塔里木大火成岩省岩浆作用等重要科学问题提供了关键制约。.（3）开展帕米尔高原横波速度结构重建和应力特征分析研究，揭示了中源地震与上地幔及壳内低速层之间的关联，为大陆地壳俯冲深度及动力响应提供了地震学证据；通过与高原内部壳幔结构、地震活动特征之间的对比，提出了大陆地壳深俯冲导致中源地震发生的动力学模型。.（4）通过横跨三江-扬子克拉通西缘的综合地球物理断面研究，以及环境噪声成像、面波和接收函数联合反演等，圈定了峨眉山大火成岩省岩浆作用的位置和规模，重建了深浅动力响应过程；利用数值模拟方法研究了岩浆底侵的热-流变学效应，揭示出二叠纪峨眉山古地幔柱大规模岩浆作用，不仅导致了扬子块体西缘的地壳垂向生长，而且显著提高了该区岩石圈流变强度，进而对现今深部过程产生了重要影响。.