报告地点：教学行政楼923会议室
报告时间：2024-08-22从10:00到11:30
报告人：常承睿（东京大学）
报告人简介：
常承睿，日本东京大学博士后研究员。本科毕业于兰州大学地质工程专业，博士毕业于京都大学地球与行星科学系；从事与地震、滑坡和火山等大规模地球物理过程相关的实验与统 计物理研究，近期主要集中于颗粒材料的摩擦行为、蠕变与破坏时间预报相关问题。
报告题目：1.岩盐颗粒介质剪切破碎引发的瞬态摩擦行为； 2.探索时间预报经验尺度律的物理背景
报告内容简介：
Probing the Physics of Empirical Scaling Law for Failure-time Forecast
探索时间预报经验尺度律的物理背景
Predicting when materials will fail or when natural hazards will occur involves complex physical processes and numerous parameters, making it a challenging task. Therefore, it is often necessary to rely on empirical approaches. One such approach, an empirical power-law scaling relation between velocity and acceleration, has proven effective and reliable for forecasting creep failure and natural events such as landslides and volcanic eruptions. While the power-law exponent is typically 2, it can evolve from 1 to 2 over time. This exponent is crucial for understanding the physical system and is essential for accurate failure-time forecasting. In this presentation, we will explore the underlying mechanisms through observation, experimentation, theory, and modeling.
预报材料何时破坏或自然灾害何时发生绝非易事，因其涉及复杂的物理过程和大量参数。因此，在实践中常常需要依赖经验方法。一种基于经验的幂律关系将变形速率与加速度关联起来，已被证明在预测滑坡和火山喷发等自然事件中具有惊人的普遍性和有效性。尽管该幂律的指数通常为 2，但它也常常从 1 演变为 2。这个指数是理解临近破坏的物理系统并进行准确预报的关键参数。在本报告中，我们将通过观测、实验、理论和模拟的方法，探索时间预报经验模型的物理机制。
Comminution-induced Transient Frictional Behavior in Sheared Granular Halite
岩盐颗粒介质剪切破碎引发的瞬态摩擦行为
Grain comminution is a prevalent phenomenon in a variety of geological settings. To better understand its influence on dry granular friction, we conducted shear experiments on breakable halite (NaCl) grains using a ring-shear apparatus at a constant slip rate under different normal stresses. Our experiments revealed distinct transient frictional behaviors: an initial regime characterized by a high friction coefficient at small slip displacements, followed by a weakening regime marked by a substantial decay in friction at larger slip displacements. The characteristic slip lengths for both regimes decreased with increasing normal stress and exhibited similar scaling exponents. Micro-X-ray tomography provided insights into the microstructural evolution, showing a transition from distributed grain comminution to progressive shear localization across these two regimes. In this presentation, we will explore the mechanisms driving these transient frictional behaviors and structural evolution, and discuss their geophysical implications for natural shear systems where grain comminution and localization are ubiquitously observed.
颗粒破碎现象在各种地质环境中普遍存在。为了更好地理解其对颗粒摩擦的影响，我们在不同的法向应力下，以恒定滑移速率对可破碎的类比颗粒介质材料——岩盐（NaCl）进行了剪切实验。实验揭示了其明显的瞬态摩擦行为：在小位移时表现出高摩擦系数的恒定阶段，以及在较大位移时摩擦显著减弱的弱化阶段。这两个阶段的特征位移随着法向应力的增加而减小，并表现出相似的缩放指数。X 射线断层扫描显示了微观结构的演变过程，从均匀的颗粒破碎流过渡到逐步的剪切局部化。在此次报告中，我们将探讨这些瞬态摩擦行为和结构变化的驱动机制，并讨论其对自然剪切系统的地球物理意义，在这些系统中，颗粒破碎和局部化极为普遍。