Mantle Anisotropic Structure and Dynamics Beneath the Western United States: Constraints from Shear-wave Splitting Analysis

在过去的50年里，地质科学的一个重大发现是，地壳和最上层的地幔被分成几十个“块”，或称构造板块。板块之间的运动导致了海洋盆地、山脉、裂谷、火山和地震的形成。 然而，尽管进行了大量的研究，驱动板块运动的力量仍然没有得到解决。正在进行的项目旨在通过测量板块运动形成的结构的强度和方向，提供有关板块运动驱动机制的关键信息。正在建立一个包含数千个剪切波分裂参数的数据库，这些参数是岩石圈变形和底层软流圈流动的测量值，作为PI为北美建立的现有剪切波分裂数据库（NA-SWS-1.1，可访问http：//www.mst.edu/~liukh/SWS）的更新版本。新的数据库与其第一版一样，将在项目实施过程中尽快公布。参与当前项目的研究人员正在收集地质和地球物理信息，以解释剪切波分裂观测结果。主要的科学问题，以解决拟议的研究，包括美国西部是否是普遍的两层各向异性，为什么科罗拉多高原和邻近地区表现出复杂的各向异性，以及什么是地幔结构和动力学的特征之间的过渡区构造活跃的美国西部和明显不活跃的大平原。

One of the major discoveries in the geological science made over the past 50 years is that the crustal and the upper-most mantle of the Earth are divided into tens of 'pieces', or tectonic plates. Movement of the plates against one another is responsible for the formation of ocean basins, mountain ranges, rifted valleys, volcanoes, and earthquakes. In spite of numerous studies, however, the forces that are driving the movement of the plates remain unresolved. The ongoing project is designed to provide critical information on the driving mechanism of plate motion, by measuring the strength and direction of the fabrics formed by the movement of the plates. A database of thousands of shear-wave splitting parameters, which are measures of deformation in the lithosphere and flow in the underlain asthenosphere, is being established as an updated version of an existing shear-wave splitting database (NA-SWS-1.1 which can be accessed at http://www.mst.edu/~liukh/SWS) that the PI established for North America. The new database, like its first version, will be made public as soon as possible over the course of the project. The researchers involved in the current project are collecting geological and geophysical information to interpret the shear-wave splitting observations. Major scientific issues to be addressed by the proposed study include whether the western US is underlain pervasively by two-layer anisotropy, why the Colorado Plateau and adjacent areas show complex anisotropy, and what are the characteristics of mantle structure and dynamics beneath the transitional zone between the tectonically active western US and apparently inactive Great Plains.