Collaborative Research: Block Kinematics of the Northwestern US

该项目通过将美国西部地区描绘成一系列弹性、旋转、相互作用的块体来研究该地区的主动变形。目标是看看这样的块表示是否满足约束以及或更好的连续体，粘流模型。为了理解是什么导致了变形，理解这两种可能表示的相对重要性是至关重要的。这项工作的目的是为了更好地了解美国西部的构造，大陆是如何变形的，以及该地区的地震潜力。利用全球定位系统（GPS）测量和反演技术，正在开发区域表面速度场，同时估计块体运动和块体边界断层附近的弹性应变积累。用球体上有限数量的旋转块体来描述区域构造的概念类似于板块构造，与大陆变形的连续体模型相反。研究区包含从太平洋-北美切变到胡安德富卡-北美辐合的重要转变。这项工作将阐明这种转变是如何在大陆内部变形中表现出来的。虽然之前已经提出并评估了块模型，但这种方法的根本区别在于它明确地模拟了短期弹性应变。因此，除了GPS对区域变形的主要限制外，它还能够纳入一个大地测量数据集，该数据集包括倾斜率和应变率。此外，它还可以利用断层滑动方向和速率、扩展速率、旋转速率和断层方向等地质数据。因此，受弹性应变影响的短期大地测量数据与反映永久变形的长期地质数据相结合——这种结合将提高我们对美国西部活动构造的理解。

This project is investigating the active deformation of the western United States by representing the region as a series of elastic, rotating, interacting blocks. The goal is to see if such a block representation satisfies the constraints as well as or better than continuum, viscous-flow models. Understanding the relative importance of the two possible representations is vital in order to understand what drives the deformation. This work is designed to lead to better understanding of the tectonics of the western US, how continents deform in general, and earthquake potential in this region. A regional, surface velocity field is being developed using Global Positioning System (GPS) measurements and applying an inversion technique that simultaneously estimates block motions and elastic strain accumulation near block-bounding faults. The concept of describing the regional tectonics by a finite number of rotating blocks on a sphere is similar to plate tectonics and is in contrast to continuum models of continental deformation. The study region contains the important transition from Pacific-North America shear to Juan de Fuca - North America convergence. This work will elucidate how this transition is manifested in deformation within the continent. While block models have been proposed and evaluated before, this approach fundamentally differs in that it explicitly models the short-term elastic strains. Hence it is able to incorporate a geodetic data set that includes tilt rates and strain rates in addition to the primary constraints on the regional deformation from GPS. Furthermore, it can use geologic data such as fault slip directions and rates, spreading rates, rotation rates, and fault orientations. Hence, geodetic data from the short-term that are subject to elastic strains are combined with longer-term geologic data that reflect permanent deformation - the combination will improve our understanding of the active tectonics of the western United States.