Collaborative Research: Towards a new framework for interpreting mantle deformation: integrating theory, experiments, and observations spanning seismic to convective timescales

地幔位于地壳的正下方，主要由坚硬的岩石组成；然而，坚硬的地幔在被推或拉的时候可以流动。这种流动的速度取决于岩石的性质，如温度，以及组成岩石的微小矿物晶体之间接触的性质。许多不同的现象可以推动地幔流动，例如：地震后经过的地震波；大陆冰盖和冰川的融化；地下水补给和提取的年度周期；以及大型湖泊的排干。这项研究利用对这些现象的观察来测量美国西部、阿拉斯加和冰岛三个地点地幔中的岩石性质和矿物晶体之间的相互作用。与此同时，实验室实验正在探索岩石样本在受控条件下如何变形。最后，新的计算机模型正在综合实验室和现场观察，以了解解释整套数据的潜在物理规律。这项研究的结果关系到从预测海平面将如何因冰盖融化而上升到了解木星卫星上的潮汐变形等一系列主题。外联和培训是该项目的关键要素。在项目期间，四名研究生和六名本科生正在接受教育。研讨会将聚集来自不同科学学科的研究人员，学习和讨论作为这项研究的一部分而开发的科学成果和计算机工具。越来越多的人认识到，描述地球对应力的机械响应的变量，如弹性模数、衰减和粘性，都与频率有关。虽然末端构件的弹性和稳态行为已被较好地理解，但关于中间过渡区域仍有许多基本问题。这项研究是一项综合研究和推广计划，将观测、实验室和建模工作结合起来，以测量地球的全谱流变响应，并阐明潜在的微物理过程。观测工作正在利用不同频率但互补的空间采样的地震和大地测量观测来表征三个地点(美国西部、冰岛和阿拉斯加)随频率变化的上地幔耗散。实验工作是研究不同温度和应力条件下位错对瞬时蠕变的影响，以及不同数量的熔体和第二固相。建模工作正在为瞬时蠕变开发新的本构定律，并在粘弹性变形代码中纳入更复杂的流变学。这项研究正在解决以下问题：(1)固体地球的宽带机械响应；(2)控制粘弹性的微观物理过程；以及(3)从大地测量数据推断稳态粘度和从地震层析成像推断热力学状态的含义。更广泛的影响包括对研究生和本科生的培训，召集120名研究人员的综合研讨会，概述了解瞬变流变学的最新进展，并塑造将决定下一个十年研究的主题和合作，以及开发交互式Jupyter笔记本，在地震衰减和瞬变流变学的背景下引入开源数据科学工具。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Earth’s mantle, which sits directly below the crust, is predominantly made of solid rock; yet the solid mantle can flow when pushed or pulled. The rate of this flow depends on the properties of the rock, such as its temperature, and on the nature of the contacts between the tiny mineral crystals that comprise the rock. The mantle can be pushed to flow by numerous different phenomena, such as: passing seismic waves after an earthquake; melting of continental ice sheets and glaciers; the annual cycle of groundwater recharge and extraction; and the draining of large lakes. This study uses observations of these phenomena to measure the rock properties and the interactions between mineral crystals in the mantle beneath three locations: the western United States, Alaska, and Iceland. Meanwhile, laboratory experiments are probing how samples of rock deform under controlled conditions. Finally, new computer models are synthesizing the lab and field observations to understand the underlying physical laws that explain the full suite of data. The results of this study have a bearing on topics that range from predicting how sea level will rise due to melting ice sheets to understanding tidal deformation on Jupiter’s moons. Outreach and training are key elements of the project. Four graduate students and six undergraduate students are being educated over the duration of the project. Workshops will bring together researchers from diverse scientific disciplines to learn and debate about the scientific outcomes and the computer tools developed as part of this study.There is emerging recognition that the variables describing Earth’s mechanical response to stress, elastic moduli, attenuation, and viscosity, are all frequency dependent. While the end-member elastic and steady-state behaviors are relatively well understood, there remain many fundamental questions regarding the intermediate transient regime. This study is an integrative research and outreach program that combines observational, laboratory, and modeling efforts to measure Earth’s full-spectrum rheological response and illuminate the underlying microphysical processes. Observational work is characterizing frequency dependent upper-mantle dissipation in three locations (western U.S., Iceland, and Alaska) using seismic and geodetic observations of different frequencies but complementary spatial sampling. Experimental work is investigating how dislocations affect transient creep under different temperature and stress conditions and with variable quantities of melt and secondary solid phases. Modeling work is developing new constitutive laws for transient creep and incorporating more sophisticated rheologies in the viscoelastic deformation code. This study is addressing questions about: (1) the broadband mechanical response of the solid Earth; (2) the microphysical processes that control viscoelasticity; and (3) the implications for inferences of steady-state viscosity from geodetic observations and of thermodynamic state from seismic tomography. Broader impacts include training of graduate and undergraduate students, a synthesis workshop that convenes 120 researchers to outline recent advances in understanding transient rheology and to shape the topics and collaborations that will dictate the next decade of inquiry, and development of interactive Jupyter notebooks that introduce open-source data-science tools in the context of seismic attenuation and transient rheology.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.