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

非技术性描述在地球表面观察到的许多地质特征和现象-如巨型山脉带，深海盆地，地震和火山-是地壳，地幔和地核中动力过程的结果。因此，提高对这些过程的认识对于理解地球的起源和发展以及减轻自然灾害至关重要。然而，目前只能利用钻孔岩芯直接观测地球最浅的部分;因此，采用了一系列计算密集型地球物理技术来对活动行星进行成像。这些技术类似于医院中用于人体成像的技术。技术说明剪切波分裂是一种基本的地球物理观测，它唯一地指示了沿着射线路径存在的方位各向异性。这种各向异性是地球软流圈和岩石圈动力学过程的结果。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。该项目将在美国东部的所有USAray可移动阵列和其他宽带地震台站测量剪切波分裂参数，并更新整个北美板块的测量结果。该数据产品包括约10，000个剪切波分裂测量结果，我们正在将其与我们为美国西部和中部制作的约16，000个测量结果合并。 我们正在利用一套程序，可靠地测量和排名的分裂参数产生一个统一的数据库，量化剪切波分裂的复杂性和可能的深度各向异性沿着。为了补充这一参考剪切波分裂数据库，我们正在计算大量的合成剪切波分裂和各向异性结构的面波研究的地球动力学正演模型计算组构从地幔流和简化的构造模型。通过这种方式，我们可以测试哪些关于各向异性起源的假设可以可靠地识别，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细化。使用这种联合的方法，我们正在解决一些重要的问题，关于地震各向异性的起源，包括岩石圈的继承和最近的软流圈流，以及北美板块下的地幔对流的性质。 此外，我们所有的测量结果以及合成波形都是公开共享的，以便其他人能够改进他们的参考模型;这确保了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.