Catastrophic Failure: what controls precursory damage localisation in rocks?

在脆弱的地球上，从人类诱发的地震活动到自然滑坡、火山喷发和地震，灾难性破坏是一种极其重要的现象。它总是与结构上的损伤集中在局部变形带上的较小断层和裂缝的形式有关，最终导致系统大小的脆性破坏沿着一个明显和紧急的断层面。然而，局部化的过程还没有被很好地理解--较小的裂缝通常就在故障发生之前，沿着早期的断层面自发地自组织，但涉及的确切机制尚未确定。许多问题仍然存在，包括：Q1--裂纹、气孔和晶界如何与施加的应力场局部相互作用，导致特定地点、方向和时间发生灾难性故障？Q2是什么决定了准静态和动态过程的相对重要性？以及Q3-为什么我们只能在某些情况下检测到灾难性故障的前兆？在这里，我们将直接解决这些问题，通过使用新开发的x射线透明形变单元和快速同步加速器x射线微层析成像整个局部化过程。我们将首次在同步加速器中以高分辨率将局部化过程的性质和演化从结构和地震一起可视化。我们将故意放慢这一过程，以成像其演变，并使用快速电子监控和反馈控制来调查潜在机制的应变率依赖关系。这将提供前所未有的对相关机制的直接观察，包括地震(产生声发射的局部裂缝)和非地震(弹性加载和无声不可逆破坏)过程对结果的贡献。这种创新的技术组合是及时、可行的，并可能改变我们对微观过程在控制系统规模故障中所起作用的理解。这些结果将为自然和人为地震活动中的类似过程提供解释模型，包括管理大型诱发事件风险的战略的比例模型测试。

Catastrophic failure is a critically-important phenomenon in the brittle Earth on a variety of scales, from human-induced seismicity to natural landslides, volcanic eruptions and earthquakes. It is invariably associated with the structural concentration of damage in the form of smaller faults and fractures on localised zones of deformation, eventually resulting in system-sized brittle failure along a distinct and emergent fault plane. However, the process of localisation is not well understood - smaller cracks spontaneously self-organise along the incipient fault plane, often immediately before failure, but the precise mechanisms involved have yet to be determined. Many questions remain, including : Q1 - How do cracks, pores and grain boundaries interact locally with the applied stress field to cause catastrophic failure to occur at a specific place, orientation and time?; Q2 what dictates the relative importance of quasi-static and dynamic processes?; and Q3 - why can we detect precursors to catastrophic failure only in some cases? Here we will address these questions directly by imaging the whole localisation process, using a newly-developed x-ray transparent deformation cell and fast synchrotron x-ray micro-tomography. We will visualise the nature and evolution of the localisation process structurally and seismically together for the first time at high resolution in a synchrotron. We will deliberately slow the process to image its evolution, and to investigate the strain-rate dependence of the underlying mechanisms, using rapid electronic monitoring and feedback control. This will provide unprecedented direct observation of the relevant mechanisms, including the contribution of seismic (local cracking producing acoustic emissions) and aseismic (elastic loading and silent irreversible damage) processes to the outcome. This innovative combination of techniques is timely, feasible, and is likely to transform our understanding of the role of microscopic processes in controlling system-size failure. The results will provide interpretive models for similar processes in natural and human-induced seismicity, including scale-model tests of strategies for managing the risk of large induced events.