我国南北地震带地壳三维结构和各向异性的研究

The well-known North-South Seismic Belt (NSSB) in China is located at the eastern margin of the vast Tibetan Plateau (TP). The NSSB possesses strong deformation, one of the world’s most active seismic regions, and strong topographic relief, which has long been an ideal location for understanding how the TP rises and grows. Various geodynamical models have been proposed for the deformation and growth without consensus, including continuum, rigid block, channel flow, and integrated block and channel flow models. Here we propose to conduct seismic imaging of the 3D structure and anisotropy of the crust and the uppermost mantle of the NSSB with the unprecedented data coverage with the combined seismic networks. The overall goal is to understand the deformation mechanisms and the behavior of the seismicity. We will use multiple methods and multiple data sets to determine 3D structure and anisotropy and to increase resolution and reduce model uncertainty. The methods include joint inversion of multiple P waves, joint inversion of dispersion, receiver function, and P model, crustal azimuthal anisotropy from receiver functions, surface wave anisotropy tomography, and Pn anisotropy tomography and the data sets include P travel times (Pg, Pn, and secondary Pg), event and continuous waveforms, receiver functions, and surface wave dispersions. We will explore the relationship of crustal structure and anisotropy and surface deformation and seismicity and compare the behaviors between different segments of the NSSB to help understand the deformation mechanisms. The proposal builds on tremendous effort that has been carried out in data acquisition and early data processing. The results have important implications not only for understanding the growth of the TP but also for hazard reduction in the region.

我国著名的南北地震带位于青藏高原东缘，有着十分剧烈的地壳变形、地震活动、和高程变化，一直以来是理解高原隆升和生长的极佳场所。人们提出许多不同的动力学模型，然而一直存在争议。本项目的总体目标是利用极好的数据积累对南北带深部成像（地壳上地幔三维结构和各向异性)和探讨区域变形机制和地震活动的规律。我们将用多种方法和多种数据来提高分辨率和减少模型不确定性。方法包括多种P波联合反演，面波频散接收函数和P模型联合反演，接收函数的地壳方位各向异性，表面波各向异性层析成像和Pn各向异性层析成像；数据包括P走时（Pg，Pn和次级Pg），事件和连续波形，接收函数和表面波频散。我们将充分利用已经获得的大量宝贵数据和已开展的工作,探讨地壳结构和各向异性与地表变形和地震活动的关系，并比较南北带不同段之间的行为，以帮助理解变形机制。研究结果不仅对理解青藏高原的生长这一基础问题，也对该区域的地震减灾有重要意义。

本项目的总体研究目标是对我国南北带进行深部成像并探讨区域变形机制和地震活动的规律。项目目标已经基本完成，同时在项目执行过程中我们在某些方面取得了杰出的成果。代表性成果包括：对青藏高原东北缘进行了联合反演，结果显示由主要断层分隔开的各个地质块体表现出明显不同的特征，表明岩石圈尺度的变形同时包括了连续缩短和局部沿断层的变形 （引用35次）；发展了一个改进的接收函数H-κ方法（H-κ-c），可以校正地壳各向异性和倾斜界面的影响，增加地壳厚度H和地壳Vp/Vs比值κ的稳定性和可靠性（引用14次）；首次利用噪声成像得到我国勒夫波成像结果，并利用瑞利波和勒夫波频散数据，反演了青藏高原东缘及东北缘S波速度结构和径向各向异性，显示出青藏东缘和东北缘不同的变形机制（引用5次）；利用Pn波成像和面波成像等结果，发现青藏高原南部印度岩石圈板片撕裂结构及其对地震和地表变形的重要影响（引用68次），引起了国际国内的广泛关注。