Collaborative Research: Shear-wave Splitting and Mantle Dynamics of the North American Plate

非技术描述在地球表面观察到的大量地质特征和现象--如巨型山带、深海盆地、地震和火山--是地壳、地幔和地核活动的动态过程的结果。因此，更好地了解这些过程对于了解地球的起源和发展以及减轻自然灾害至关重要。然而，目前只能使用钻孔的岩芯直接观测到地球最浅的部分；因此，一系列计算密集型地球物理技术被应用于成像这颗活跃的行星。这些技术类似于医院中用于对人体成像的技术。技术说明横波分裂是一种基本的地球物理观测，它唯一地表明沿着射线路径存在方位各向异性。这种各向异性是地球软流圈和岩石圈动态过程的结果。然而，剪切波分裂的动态解释需要均匀的、高质量的测量和定量的正演模型。该项目将测量美国东部所有USArray可移动阵列和其他宽带地震台站的横波分裂参数，并更新整个北美板块的测量结果。该数据产品包括约10,000个横波分裂测量，我们正在将这些测量与我们通过EarthScope为美国西部和中部产生的约16,000个测量结果合并，NSF先前提供了资金。我们正在利用一套程序来可靠地测量和排序分裂参数，以产生一个统一的数据库，量化横波分裂的复杂性和沿途可能的各向异性深度。为了补充这个参考横波分裂数据库，我们通过计算地幔流动组构和简化的构造模型，计算了大量合成横波分裂和各向异性结构的地球动力学正演模型，用于面波研究。这样，我们就可以测试哪些各向异性起源的假设可以可靠地辨别出来，哪些构造情景最能反映观测结果，以及如何指导我们对大陆和上地幔结构和动力学的理解的区域性细化。利用这一联合方法，我们正在解决有关地震各向异性起源的一些重要问题，包括岩石圈的继承性和最近的软流层流动，以及北美板块下方地幔对流的性质。此外，我们的所有测量以及合成波形都是公开共享的，以便其他人能够改进其结果参考模型；这确保我们的数据产品将对广泛的地球科学问题产生重大影响。

Non-technical DescriptionNumerous geological features and phenomena observed on the surface of the Earth -- such as giant mountain belts, deep ocean basins, earthquakes, and volcanoes -- are the results of dynamic processes operating in the Earth's crust, mantle, and core. Therefore, an improved understanding of these processes are essential for the understanding of the origin and development of the Earth and for mitigation of natural hazards. At the present time, however, only the shallowest part of the Earth can be observed directly using cores from drill holes; consequently, an array of computing-intensive geophysical techniques are applied to image the active planet. Those techniques are similar to those used in the hospital to image the human body.Technical DescriptionShear-wave splitting is a fundamental geophysical observation that uniquely indicates the presence of azimuthal anisotropy along the ray path. Such anisotropy is the result of dynamic processes in the Earth's asthenosphere and lithosphere. However, dynamic interpretation of shear-wave splitting requires homogeneous, high quality measurements, and quantitative forward models. This project will measure shear-wave splitting parameters at all of the USArray Transportable Array and other broadband seismic stations in the eastern U.S. and update measurements throughout the North American plate. The data product includes ~10,000 shear-wave splitting measurements that we are merging with ~16,000 measurements that we produced for the western and central U.S. with NSF prior funding via EarthScope. We are utilizing a set of procedures for reliably measuring and ranking the splitting parameters for producing a uniform database, quantifying shear-wave splitting complexity and likely depth of anisotropy along the way. To complement this reference shear-wave splitting database, we are computing a large number of geodynamic forward models of synthetic shear-wave splitting and anisotropic structure for surface wave studies by computing fabrics from mantle flow and simplified tectonic models. This way, we can test which hypotheses for the origin of anisotropy can be reliably discerned, which tectonic scenarios best reflect observations, and how to guide regional refinement of our understanding of continental and upper mantle structure and dynamics. Using this joint approach, we are addressing a number of significant questions regarding the origin of seismic anisotropy, including lithospheric inheritance and recent asthenospheric flow, and the nature of mantle convection underneath the North American plate. In addition, all our measurements, as well as synthetic waveforms, are being openly shared so as to allow others to refine their resulting reference models; this ensures our data product will have a significant impact on a broad range of Earth science questions.