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，地球的地壳和最上层的地幔被分成了几十个“块”，即构造板块。板块之间相互碰撞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未得到解决。正在进行的项目旨在通过测量由板块运动形成的织物的强度和方向，提供关于板块运动驱动机制的关键信息。目前正在建立一个包含数千个剪切波分裂参数的数据库，这些参数用于测量岩石圈的变形和下层软流层的流动，作为PI为北美建立的现有剪切波分裂数据库（NA-SWS-1.1，可在http://www.mst.edu/~liukh/SWS上访问）的更新版本。与第一个版本一样，新数据库将在项目过程中尽快向公众公布。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。提出的研究要解决的主要科学问题包括美国西部是否普遍存在两层各向异性，为什么科罗拉多高原及其邻近地区表现出复杂的各向异性，以及在构造活跃的美国西部和明显不活跃的大平原之间的过渡带下的地幔结构和动力学特征是什么。

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.