Constraints on the Rheology of the Lithosphere in Western North America from Observationally Driven Dynamic Models

这项研究要研究的问题涉及北美西部的三维动力学。其目标是结合三维全球地幔环流的影响，以及详细的岩石圈结构。该项目将把从EarthScope的USArray数据中获得的岩石圈和上地幔结构的最新结果纳入模型中。这些模型将产生应变率、岩石圈表面运动和上地幔结构的预测。3-D模型的基准测试表明，可靠的结构信息导致对活动变形场负责的应力的可靠估计，而与有效粘性绝对值的精确知识无关。在给定结构约束的情况下，我们将调查满足地表速度观测、岩石圈变形指标和世界应力图应力方向的模型范围。这种模拟对作用在岩石圈内的深度综合应力的大小施加了限制，因此也对岩石圈的流变性施加了限制。我们建议使用最终的应力大小和深度综合岩石圈有效粘度的模型约束，以及热流测量、应变率和地壳厚度估计来研究北美西部下地壳和上地幔的流变性参数的界限。最后，我们建议研究三维区域岩石圈动力学模型，以解决中地壳内流变薄弱带的影响，它们对随深度变化的水平流动的影响，以及对地幔流动耦合的影响。地球岩石圈内的应力负责最终在地震中沿断层释放的应变。在地质时间尺度上，这种永久应变导致造山和盆地形成。现在，高速计算机使研究导致岩石圈内这些应力和应变的过程的规模、规模和分布成为可能。这些过程包括地幔对流，以及与地形和地壳厚度和密度变化有关的力。地震学观测提供了地壳厚度和密度变化的约束，以及地球对流地幔内结构的图像。这些图像或速度变化，提供了驱动地幔对流的密度变化的信息。该项目将使用大量新的约束(由NSF资助的EarthScope项目提供)对北美西部下面的结构进行限制，以限制岩石圈内作用的应力的大小和分布。模型包括力平衡的有限元解，将包括三维地幔流动的影响，以及岩石圈地形和结构。模型将进一步受到板块运动表面观测(从高精度GPS获得)和热流测量的限制。这项研究将有助于描绘岩石圈内应力状态的大小和分布。这一关于应力状态的结果，包括其与具体驱动机制的联系，将为研究震源物理和一般地震周期提供一个基本框架。这项工作还将为大陆形变如何在更长的时间尺度上演化提供重要的见解。最后，该项目将为进入劳动力大军的科学家提供技术培训，他们将提高解决问题和沟通的技能，适用于工业和学术环境。

The problem to be studied in this research involves the three dimensional dynamics of western North America. The objective is to incorporate the effects of 3-D global mantle circulation, along with detailed lithosphere structure. The project will incorporate latest results of lithosphere and upper mantle structure, obtained from EarthScope's USArray data, into the models. The models will yield predictions of strain rate, surface motion of lithosphere, and upper mantle structure. Benchmarking with 3-D models indicates that reliable structural information leads to reliable estimates of the stresses responsible for the active deformation field, independent of precise knowledge of absolute values of effective viscosity. Given constraints on the structure, we will investigate the range of models that satisfy surface observations of velocity, lithosphere deformation indicators, and World Stress Map stress orientations. This modeling places a bound on the magnitudes of depth-integrated stresses acting within the lithosphere and, as such, places bounds on the lithosphere rheology. We propose to use final model constraints on stress magnitudes and depth integrated lithosphere effective viscosities, together with heat flow measurements, strain rates, and crustal thickness estimates to investigate the bounds on rheological flow parameters for the lower crust and upper mantle beneath Western North America. Finally, we propose to investigate 3-D regional lithosphere dynamic models to address the influence of rheologically weak zones within the middle crust, their impact on depth-dependent horizontal flow, along with effects on coupling of mantle flow.Stresses acting within the Earth's lithosphere are responsible for strain that is ultimately released in earthquakes along faults. Over geologic time scales, this permanent strain results in mountain building and basin formation. High-speed computers now make it possible to investigate the magnitude, scale, and distribution of processes that lead to these stresses and strains within the lithosphere. These processes include mantle convection, along with forces associated with topography and variations in thickness and density of the Earth's crust. Seismological observations provide constraints on variations of thickness and density of the crust, along with images of structure within the Earth's convecting mantle. These images, or velocity variations, yield information on the density variations that drive mantle convection. This project will use a vast amount of new constraints (provided by the NSF funded EarthScope project) on structure beneath western North America to place bounds on the magnitude and distribution of stresses acting within the lithosphere. Models, which involve finite-element solutions of force-balance, will incorporate the effects of three-dimensional mantle flow, along with lithosphere topography and structure. Models will be further constrained by surface observations of plate motions (obtained from high precision GPS), and heat flow measurements. This research will help delineate the magnitude and distribution of the state of stress within the lithosphere. This result on the state of stress, including its link with the specific driving mechanisms, will provide a fundamental framework for investigations of earthquake source physics and the earthquake cycle in general. This work will also provide important insights into how continental deformation evolves over longer time scales. Finally, project will provide technical training to scientists who will enter the work force with improved skills involving problem solving and communication, applicable in both industrial and academic settings.