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.

在这项研究中要研究的问题涉及北美西部的三维动态。目的是结合3-D全球地幔循环的影响以及详细的岩石圈结构。该项目将结合岩石圈和上地幔结构的最新结果，这些结构从Earthscope的USARRAY数据获得的模型中。这些模型将产生应变速率，岩石圈表面运动和上地幔结构的预测。使用3-D模型的基准测试表明，可靠的结构信息会导致对主动变形场的应力的可靠估计，而与有效粘度的绝对值无关。给定对结构的限制，我们将研究满足速度，岩石圈变形指标和世界应力映射应力方向的表面观测的模型范围。这种建模将作用在岩石圈内的深度综合应力的大小上，因此将其限制在岩石圈流变学上。我们建议在应力尺寸和深度整合岩石圈的有效粘度上使用最终模型约束，以及热流量测量，应变速率和地壳厚度估计，以研究下地壳下地壳和北美西部下层地震的流变流量参数的边界。最后，我们建议研究3-D区域岩石圈动态模型，以解决中壳中流变学弱区的影响，它们对深度依赖水平流动的影响以及对地幔流的偶联的影响。在地球岩石圈内作用在地球层内作用的压力是在地震中最终释放出沿断层的地震造成的。在地质时间尺度上，这种永久性应变会导致山区建筑和盆地形成。现在，高速计算机可以研究导致岩石圈内这些应力和菌株的过程的大小，规模和分布。这些过程包括地幔对流，以及与地形相关的力以及地壳的厚度和密度变化。地震学观察结果对地壳的厚度和密度的变化以及地球对流地幔内的结构图像提供了限制。这些图像或速度变化产生有关驱动地幔对流的密度变化的信息。该项目将在北美西部的结构上使用大量的新约束（由NSF资助的Earthscope项目提供），以在岩石圈内作用的压力的幅度和分布限制。涉及有限元元素溶液的模型将结合三维地幔流的影响以及岩石圈地形和结构。模型将受到板运动的表面观测（从高精度GPS获得）和热流量测量结果进一步限制。这项研究将有助于描绘岩石圈内应力状态的大小和分布。这对压力状态的结果，包括其与特定驾驶机制的联系，将为研究地震源物理学和地震周期的研究提供一个基本框架。这项工作还将为大陆变形如何在更长的时间尺度上演变而来。最后，项目将向科学家提供技术培训，这些科学家将进入劳动力，具有提高的技能，涉及解决问题和沟通的技能，适用于工业和学术环境。