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

观测驱动的动力学模型对北美西部岩石圈流变学的约束

• 批准号: 1246971
• 负责人: William Holt
• 金额: $ 14.9万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-06-01 至 2017-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1246971&HistoricalAwards=false
• 关键词: Constraints; Rheology; Lithosphere; Western; North

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.

本研究所要研究的问题涉及北美西部的三维动力学。其目的是将三维全球地幔环流的影响，沿着详细的岩石圈结构。该项目将把从EarthScope的USAray数据中获得的岩石圈和上地幔结构的最新结果纳入模型。该模型将产生应变率，岩石圈表面运动和上地幔结构的预测。基准与3-D模型表明，可靠的结构信息导致可靠的估计负责主动变形场的应力，独立的精确知识的绝对值的有效粘度。考虑到结构上的限制，我们将研究满足速度、岩石圈变形指标和世界应力图应力方向的表面观测的模型范围。这种建模的地方上的深度积分应力的大小作用在岩石圈内的约束，因此，地方上的岩石圈流变学的界限。我们建议使用最终的模型约束应力大小和深度集成岩石圈有效粘度，热流测量，应变率和地壳厚度估计，调查下地壳和上地幔下北美西部的流变流动参数的界限。最后，我们建议研究3-D区域岩石圈动力学模型，以解决中地壳内的流变学弱带的影响，它们对深度相关的水平流动的影响，沿着与地幔流耦合的影响。地球岩石圈内的应力作用是负责应变，最终释放在地震沿着断层。在地质年代尺度上，这种永久性的应变导致了造山和盆地的形成。高速计算机现在使得研究岩石圈内导致这些应力和应变的过程的大小、规模和分布成为可能。这些过程包括地幔对流，沿着与地形有关的力以及地壳厚度和密度的变化。地震观测提供了地壳厚度和密度变化的限制，沿着提供了地球对流地幔内部结构的图像。这些图像，或速度变化，产生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）对北美西部下方的结构进行约束，以确定岩石圈内应力的大小和分布。模型包括力平衡的有限元解，将把三维地幔流的影响与岩石圈地形和结构沿着考虑在内。模型将进一步受到板块运动的地表观测（从高精度GPS获得）和热流测量的约束。这项研究将有助于描述岩石圈内应力状态的大小和分布。应力状态的这一结果，包括其与特定驱动机制的联系，将为震源物理学和地震周期的一般调查提供一个基本框架。这项工作也将提供重要的见解大陆变形如何演变在较长的时间尺度。最后，项目将为科学家提供技术培训，这些科学家将进入劳动力市场，提高解决问题和沟通的技能，适用于工业和学术环境。