Collaborative Research: The Effects of Water and Lithology on the Strength of the North American Lithosphere

非技术性概述要全面了解造山运动和地震过程，需要了解大陆流动强度的三维变化。流动强度的测量是EarthScope的主要目标之一，因为它们是了解地震和火山活动的时间和空间分布以及北美随时间演变的关键。然而，表征流动强度是具有挑战性的，因为强度对三个独立的物理特性-温度，岩石类型和含水量-非常敏感，其影响不容易使用常用的地球物理成像技术区分。该项目确定了几种不同的地球物理测量方法，这些方法可以结合起来，分离地壳和上地幔中温度、岩石类型和水的影响。此外，该项目正在支助三名研究生的教育和开发供研究生课堂使用的软件工具。 最后，该项目还提供了地图和其他数据产品，这些产品对科学家了解未来地震、火山爆发的可能性以及深部经济矿藏的潜力等各种主题非常有用。技术说明该项目旨在确定温度、水和岩性对北美大陆岩石圈强度的相对影响。调查人员正在利用最上层地幔地震速度和地表热流测量来估计温度变化;根据重力和地震接收器功能数据的组合来确定地壳岩性的特征;并将这些数据与岩石圈抗弯刚度（抗弯强度的一种综合测量）的测量相结合，以评估水对流动流变学的其余影响。这种新的方法来表征物理性质的变化，使在原位估计的岩石圈的全三维流动流变学，并提供新的见解的动态过程中的热量和流体通量，确定流动性与大陆岩石圈的稳定性。当与岩石圈质量密度变化的新约束相结合时，这些属性有望彻底改变地球科学界对岩石圈演化，变形和动力学过程的理解。该补助金支持三名研究生的研究工作。科罗拉多州立大学PI和两个硕士学位。学生们正在估计地热变化和相关的不确定性，并开发了一系列教学工具，向地球科学本科生演示岩石圈挠曲和流变学的概念。犹他州州立大学的PI和学生正在估计各向异性抗弯刚度、地壳岩性和厚度，并使用组合测量来模拟岩石圈的含水量和流变学。

Nontechnical SummaryA full understanding of mountain-building and earthquake processes requires knowledge of three-dimensional variations in flow strength of continents. Measurements of flow strength are among the major goals of EarthScope, because they are key to understanding the timing and spatial distribution of earthquakes and volcanism, as well as the evolution of North America through time. Characterizing flow strength is challenging, however, because strength is very sensitive to three independent physical properties -- temperature, rock-type, and water content -- whose effects are not easily distinguished using commonly-used geophysical imaging techniques. This project identifies several diverse geophysical measurements that can be combined to separate the effects of temperature, rock type and water in the Earth's crust and upper mantle. In addition, this project is supporting the education of three graduate students and the development of software tools for use in graduate classrooms. Finally, this project is providing maps and other data products that are widely useful to scientists working to understand such diverse topics as likelihood of future earthquakes, volcanic eruptions, and the potential for economic mineral deposits at depth.Technical Description This project seeks to determine the relative effects of temperature, water and lithology on strength of the North American continental lithosphere. The investigators are estimating temperature variations using uppermost mantle seismic velocities and surface heat flow measurements; characterizing crustal lithology from a combination of gravity and seismic receiver function data; and combining these with measurements of lithospheric flexural rigidity (an integral measure of bending strength) to assess the remainder effects of water on flow rheology. This novel approach to characterizing physical property variations enables in situ estimation of fully three-dimensional flow rheology of the lithosphere, and lends new insight into the dynamical processes of heat and fluid flux that determine mobility versus stability of continental lithosphere. When combined with new constraints on lithospheric mass density variations, these properties promise to revolutionize the Earth Science community's understanding of lithospheric evolution, deformation and dynamical processes. The grant supports research efforts by three graduate students. The Colorado State University PI and two M.S. students are estimating geothermal variations and associated uncertainties, and also developing a series of teaching tools to demonstrate concepts of lithospheric flexure and rheology to undergraduate Earth science students. The Utah State University PI and student are estimating anisotropic flexural rigidity, crustal lithology and thickness, and using the combined measurements to model the water content and rheology of the lithosphere.