Microphysics of evolving rock viscosity in the seismic and glacial cycles

尽管是力量的缩影，但地球表面下的坚硬岩石可以惊人地以惊人的速度在人类时间尺度上流动，影响与社会相关的过程。该项目旨在根据岩石中运行的基本过程提供描述这种流动的新方程。大地震和冰盖融化导致地球表面的偏转，而下面热岩的粘性流动促进了这种偏转。这种变形产生了重要的反馈。在地震周期中，地震引起断层带下岩石的粘性流动，影响未来地震的空间和时间分布。在冰川周期中，融化的冰盖下岩石的粘性流动会引起地面抬升，从而影响海平面的变化。因此，模拟这些系统需要了解地球下地壳和上地幔中岩石的粘度。不幸的是，这些岩石的粘度并不是恒定的，而是在外力发生变化时经历短暂的演变。虽然我们知道这种粘度演变的发生，但我们不知道为什么。如果不知道控制粘性演化的微尺度过程，我们就无法建立方程来可靠地预测地震和冰川周期中地球上岩石的流动。在面临地震风险的人口迅速扩大，冰盖动力学模型具有前所未有的重要性的时候，开发支撑这些系统的岩石粘度演化的新模型是至关重要的。确定控制岩石粘度演化的微物理过程需要雄心勃勃的多学科方法。研究的每一项内容都将集中于对材料科学前沿的技术进行新的调整，以分析关键的地质矿物。实验将在高达1500摄氏度的温度下进行，并将通过施加与地震类似的瞬时变化的作用力来诱导粘度演变。第一次，部分实验将在扫描电子显微镜内进行，允许在测试期间直接对样品进行成像。我们将使用由我们团队首创的最先进的显微镜技术来分析样品的微观结构，以测量晶格的扭曲和捕获在其中的力。结合力学数据和微观结构观察，将提供必要的新见解，以确定在矿物晶格中操作的导致其粘度变化的关键过程。实验室的解释将受到两个关键测试。为了检查解释的一致性和稳健性，我们将使用最新的变形晶体材料模型。我们将采用这些为模拟金属而开发的模型来分析地质材料。实验室实验与天然岩石的相关性将通过比较两种环境下矿物的微观结构来检验。我们将利用主要断裂带深部的样本，直接记录下地壳和上地幔的粘性流动。从实验、微观结构分析和模拟中获得的关键信息将用于构建和校准描述粘性演化的新方程。这些方程式将首次建立在对具体潜在过程的严格分析基础上。这些方程将解锁下一代大型模型，其中包括地震和冰川周期中粘度演变的影响。在这个项目中产生的力学和微观结构数据将免费提供，提供一个新的和独特的数字资源。同样，该项目中首创的技术将在地质材料动力学方面开辟新的前沿。

Despite being the epitome of strength, the solid rocks below Earth's surface can flow surprisingly rapidly over human timescales, impacting processes of societal relevance. This project aims to deliver new equations describing this flow based on the underlying processes operating in the rocks.Major earthquakes and the melting of ice sheets cause deflections of Earth's surface that are facilitated by viscous flow of the hot rocks below. This deformation creates important feedbacks. During the seismic cycle, earthquakes induce viscous flow of rocks beneath the fault zone that impacts the spatial and temporal distributions of future earthquakes. During the glacial cycle, viscous flow of rocks beneath melting ice sheets causes ground uplift that impacts sea-level change. Therefore, modelling these systems requires knowledge of the viscosity of rocks in Earth's lower crust and upper mantle.Unfortunately, the viscosities of these rocks are not constant but instead undergo a transient evolution whenever there is a change in the applied forces. Whilst we know that this viscosity evolution occurs, we do not know why. Without knowing the microscale processes that control the viscosity evolution, we cannot formulate equations that reliably predict flow of rocks in the Earth over the seismic and glacial cycles. At a time when populations exposed to seismic risk are rapidly expanding and when the modelling of ice-sheet dynamics is of unprecedented importance, it is critical to develop new models for the viscosity evolution of the rocks that underpin these systems.Deciphering the microphysical processes that control the viscosity evolution of rocks requires an ambitious multidisciplinary approach. Each element of the research will be centred on the novel adaptation of techniques from the forefront of the materials sciences to analyse key geological minerals. Experiments will be conducted at temperatures up to 1500 degrees Celcius and will induce viscosity evolution by imposing instantaneous changes in the applied forces, analogous to those imposed by earthquakes. For the first time, a subset of the experiments will be performed inside a scanning electron microscope allowing the samples to be directly imaged during the tests. The microstructures of the samples will be analysed using state-of-the-art microscopy techniques, pioneered by our group, to measure distortions of the crystal lattices and the forces trapped within them. The combined mechanical data and microstructural observations will provide the new insights necessary to determine the key processes operating in the crystal lattices of the minerals that cause their viscosities to evolve.The interpretations from the laboratory will be subject to two critical tests. To check the consistency and robustness of the interpretations, we will employ the latest models of deforming crystalline materials. We will adapt these models, developed to simulate metals, to analyse geological materials. The relevance of the laboratory experiments to natural rocks will be tested by comparing the microstructures of minerals from both settings. We will utilise samples from the deep portions of major fault zones that provide direct records of viscous flow in the lower crust and upper mantle.The critical information gained from experiments, microstructural analyses, and modelling will be used to construct and calibrate new equations describing viscosity evolution. For the first time, the equations will be based on rigorous analyses of the specific underlying processes. These equations will unlock the next generation of large-scale models that incorporate the impacts of viscosity evolution in the seismic and glacial cycles. The mechanical and microstructural data generated in this project will be made freely available, providing a new and unique digital resource. Similarly, the techniques pioneered in this project will open new frontiers in the dynamics of geological materials.