Testing the hypothesis of pervasive two-layer azimuthal anisotropy beneath North America

剪切波分裂参数（快速偏振方向和分裂时间）越来越多地被各种各样的地球科学家用于了解地球深部内部的结构和动力学。剪切波分裂是由冷岩石圈内冻结的化石各向异性引起的，还是由下伏软流圈中的现今地幔流引起的，还是两者的结合引起的，至今仍是一个有争议的话题。虽然地球科学界的共识是，剪切波分裂测量是了解地球深部结构和动力学的基础，但迄今为止，仍然缺乏一个关于分裂参数的连贯的综合数据库。在过去的几年里，大量高质量的数据被添加到IRIS（地震学联合研究机构）DMC（数据管理中心）的数据档案中。此外，在过去几年中，网络中增加了更多的宽带永久站，许多短周期站也在同一时期更新为宽带站。最后，正在进行的USAray中的台站正在提供大量新数据。最近可用的数据集显着改善分裂参数的空间覆盖范围，特别是在北美大陆的稳定部分。PI和她的研究小组正在使用他们开发的可靠测量和主观排名剪切波分裂测量的强大程序来测量所有宽带站的剪切波分裂参数。由于该项目，正在获得大约10 000个定义明确的台站-事件对。建议的研究的第一个目标是生成一个数据库的个人（不站平均）分裂参数使用数据集访问IRIS DMC。第二个组成部分是使用分裂参数的综合相干数据库来检验Marone和Romanowicz [2007]的假设，他们通过地表波形和剪切波分裂观测的联合反演，提出了一个普遍的两个-北美中部和东部地下各向异性层模型。从拟议的工作预期的结果将用于广泛的地球科学家，以解决广泛的关于地球深层内部的结构和动力学的基本问题。例如，如果普遍存在的两层各向异性的假设通过了使用拟议研究产生的相干剪切波分裂数据库的测试，地球动力学建模者将在其计算中部署两层模型，矿物物理学家将进行实验，在岩石圈和软流圈解耦的假设下研究相变和水的影响。

Shear-wave splitting parameters (fast polarization direction and splitting time) have been increasingly used by a wide variety of geoscientists for the understanding of the structure and dynamics of the Earth's deep interior. Whether the observed shear-wave splitting is originated from fossil anisotropy frozen within the cool lithosphere, is produced by present-day mantle flow in the underlying asthenosphere, or is from combination of the two is still a debated topic. While it is a consensus in the earth science community that shear-wave splitting measurements are fundamental for the understanding of the structure and dynamics of the Earth's deep interior, so far there is still a lack of a coherent comprehensive database for the splitting parameters. Over the past several years a significant amount of high-quality data have been added to the data archives at the IRIS (Incorporated Research Institutions for Seismology) DMC (Data Management Center). In addition, a lot more broadband permanent stations have been added to the network over the past several years, and many short-period stations have been updated into broadband stations over the same period of time. Finally, stations in the on-going USArray are providing a large amount new data. The recently available data sets significantly improve the spatial coverage of splitting parameters, especially in the stable part of the North American continent. The PI and her research group are measuring shear-wave splitting parameters at all the broadband stations using a robust procedure that they developed to reliably measure and subjectively rank shear-wave splitting measurements. About 10,000 well-defined station-event pairs are being obtained as a result of the project. The first goal of the proposed study is to generate a database of individual (not station averaged) splitting parameters by using datasets accessible from the IRIS DMC. The second component is to use the comprehensive coherent database of splitting parameters to test the hypothesis of Marone and Romanowicz [2007], who, by joint inversion of surface waveforms and shear-wave splitting observations, suggested a pervasive two-layer anisotropic model beneath central and eastern North America.Expected results from the proposed work will be used by a broad spectrum of geoscientists to address a wide range of fundamental questions regarding the structure and dynamics of the Earth's deep interior. For instance, if the hypothesis of pervasive two-layer anisotropy passed the test using the coherent shear-wave splitting database to be produced by the proposed study, geodynamic modelers will deploy the two-layer model in their calculations, and mineral physicists will perform experiments to study phase change and effects of water under the assumption that the lithosphere and the asthenosphere are decoupled.