Crustal and Uppermost Mantle Anisotropy Across Tibet and East China

美国大陆上同时部署的大型地震仪阵列的安装（例如，USAray）和中国（例如，中国地震台阵（China Array）的建立，推动了地震面波层析成像新方法的发展，这些新方法以前所未有的分辨率和可靠性提供了有关地震各向异性的新型定性信息。地震各向异性是地震波速度的方向依赖性，它提供了有关组成地球的矿物的成分和取向（结构）的信息。新的分析方法的初步应用揭示了西藏地壳各向异性的分层性，其中上地壳和下地壳各向异性组构的取向和倾角有很大差异。这导致了一种假设，即这些观察到的特征是由地壳较浅和较深深度的不同变形模式造成的：上地壳的脆性变形和中地壳至下地壳可能部分熔融的韧性流动。对地壳各向异性进行新的地震评估的同时，对地壳矿物组合各向异性进行了改进的实验室测量。地震学和地壳各向异性岩石学之间日益增长的协同作用使人想起早期对地幔各向异性的研究。从这种协同作用中，一套统一的跨学科研究目标正在出现，其中两个从根本上推动了这项工作。首先是绘制大陆地壳的各向异性图，以说明正在进行的和化石地壳变形。第二个是照亮的垂直一致性的活动变形的调查之间的关系，推导出大地测量数据，地壳和地幔各向异性解释的应变。这项工作是基于环境噪声和地震数据，提供各向同性和方位各向异性的瑞利和爱波群和相位速度，现在可以反演的信息，通过贝叶斯蒙特卡罗形式主义，深度相关的地壳弹性张量的倾斜六角形对称介质。拟议的工作将通过以下方式进行：（1）增加新的测量方法，以提高估计地壳深部和上地幔各向异性的能力，（2）扩大研究的空间范围，以便在地质不同的区域之间进行比较（包括西藏东部和西部及其周边地区），（3）引入新的数据类型（特别是接收器函数）以帮助解决当前方法中的模糊性，以及（4）执行数值模拟以测试当前正演计算方法并探索表面波振幅测量中的各向异性的特征。这项工作的一个关键组成部分是估计的不确定性，使用蒙特卡洛和相关的贝叶斯统计的主要测量，可以与所产生的地震模型。

The installation of large simultaneously deployed on-continent arrays of seismometers in the US (e.g., USArray) and China (e.g., Chinese Earthquake Array, China Array) has motivated the development of new methods of seismic surface wave tomography that provide qualitatively new types of information about seismic anisotropy at unprecedented resolution and reliability. Seismic anisotropy is the directional dependence of seismic wave speeds, which provides information about the composition and orientation (fabric) of the minerals that compose the Earth. Preliminary applications of the new analysis methods reveal the stratification of anisotropy in the Tibetan crust in which the orientation and inclination of the anisotropic fabrics of the upper and lower crust differ substantially. This has led to the hypothesis that these observed features result from different modes of deformation at work at shallower and deeper depths in the crust: brittle deformation in the upper crust and ductile flow with possible partial melt in the middle to lower crust. The new seismic estimates of crustal anisotropy are occurring in parallel with improved laboratory measurements of the anisotropy of crustal mineral assemblages. This growing synergy between the seismology and the petrology of crustal anisotropy is reminiscent of earlier studies of mantle anisotropy. From this synergy a set of unifying cross-disciplinary research objectives is emerging, two of which fundamentally motivate this work. The first is to map anisotropy in the continental crust to illuminate on-going and fossil crustal deformation. The second is to illuminate the vertical coherence of active deformation by investigating the relationship between ongoing surface deformation, deduced from geodetic data, with crustal and mantle anisotropy interpreted in terms of strain. The work is based on ambient noise and earthquake data which provide both isotropic and azimuthally anisotropic information about Rayleigh and Love wave group and phase speeds that now can be inverted, via a Bayesian Monte Carlo formalism, for the depth-dependent crustal elastic tensor for a tilted hexagonally symmetric medium. The proposed work proceeds by: (1) adding new measurements to improve the ability to estimate anisotropy in the deep crust and uppermost mantle, (2) extending the spatial extent of the study to allow comparisons to be made between geologically distinct regions (including East and West Tibet and its surrounding regions), (3) introducing new types of data (notably receiver functions) to help to resolve ambiguities in the current method, and (4) performing numerical simulations to test the current forward computation method and explore the signature of anisotropy in surface wave amplitude measurements. A key component of this work is the estimation of uncertainties using Monte Carlo and related Bayesian statistics from primary measurements that can be associated with the resulting seismological models.