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

测试北美地下普遍存在的两层方位各向异性的假设

• 批准号: 0739015
• 负责人: Kelly Liu
• 金额: $ 12.27万
• 依托单位: Missouri University of Science and Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-01-01 至 2010-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0739015&HistoricalAwards=false
• 关键词: Testing; hypothesis; pervasive; two; layer

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.

剪切波分裂参数（快速偏振方向和分裂时间）已越来越多地被地球科学家用于了解地球深层内部的结构和动力学。观察到的剪切波分裂是否源自冷岩石圈内冻结的化石各向异性，是由当今底层软流圈中的地幔流产生的，还是两者的结合，仍然是一个有争议的话题。虽然地球科学界一致认为，剪切波分裂测量对于理解地球深层结构和动力学至关重要，但迄今为止仍然缺乏一个连贯的综合分裂参数数据库。在过去的几年中，大量高质量数据已添加到 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点，并且许多短期站点同期已更新为宽带站点。最后，正在进行的 USArray 中的站点正在提供大量新数据。最近可用的数据集显着提高了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程序来测量所有宽带站的剪切波分裂参数，该程序是为了可靠地测量剪切波分裂测量值并对其进行主观排序。该项目的结果是获得了大约 10,000 个明确定义的站点-事件对。拟议研究的第一个目标是通过使用可从 IRIS DMC 访问的数据集来生成单个（非站点平均）分裂参数的数据库。第二个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，他们通过表面波形和剪切波分裂观测的联合反演，提出了中心层下方普遍存在的双层各向异性模型和北美东部。拟议工作的预期结果将被广泛的地球科学家用来解决有关地球深层内部结构和动力学的广泛基本问题。例如，如果普遍两层各向异性的假设通过了所提出的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水的相变和影响。