On the edge?

该项目解决了当前向净零碳经济转型的迫切需要。许多实际的解决方案涉及我们脚下的土地工程，例如通过地热能生产，放射性废物处理，以及二氧化碳或氢气的地下储存。问题是，这些活动给地下水库或储存地点增加了新的压力，这些地下水库或储存地点已经受到了板块构造造成的环境压力。因此，即使是很小的额外应力也有引发地震的风险，可能导致地面运动造成破坏或滋扰，和/或使有害流体逸出地表，从而使公众对这种解决方案失去信心。例如，尽管引入了“交通灯系统”来管理风险，但英国陆上水力压裂行业还是在兰开夏郡引发了2.9级的地震。英国交通灯系统以0.5（琥珀色）的阈值来调整车辆运行，或者以1.0（红色）的阈值来停止车辆运行。阻止2.9级地震的失败导致了水力压裂行业的暂停，直到今天。如果类似的命运等待着涉及地下工程的净零解决方案，那将是悲惨的。在这里，我们要解决的问题是：我们能做得更好吗？制定有效的风险管理策略的主要障碍之一是，我们常常不知道在工程系统的规模上，地球离失败有多近——我们是否处于失败的“边缘”？地球对小应力扰动的敏感性是高度可变的，这是该领域最大的“已知未知”之一。在这里，我们将进行一系列的实验，以了解在不同的启动应力下触发断裂和地震的过程，看看我们是否可以在开始运行之前描述这种敏感性，并在运行期间比目前的交通信号灯系统更好地控制极端事件的风险。我们将使用对应力变化敏感的精确测量地震波速度变化的新方法，并利用这些方法以及诱发地震活动的其他属性，如事件率、断层或裂缝类型以及相关变形量，看看我们是否可以在受控环境中做得更好。我们将在实验室建立一个比例模型系统，在那里我们可以模拟现场条件下的应力和流体压力。当我们通过改变应力或孔隙压力使岩石变形时，我们将以微裂缝的形式记录由破坏引起的微小微地震，并监测地震速度和流体渗透率的变化。我们特别感兴趣的是与非常小的应力扰动相关的微小但可检测的速度瞬变（阶跃变化之后是逐渐衰减）。瞬态被认为是由于应力变化时材料突然引起的损伤和随后较慢的愈合引起的。它们在地球上的各种环境中都被观察到，但它们的原因仍然是个谜。在这里，我们将在同步加速器中进行现场实验，因此我们可以“看到”孔隙尺度上变形的实际过程。我们将建造一个独特的，专门建造的便携式变形钻机，以保持英国在这类工作中的全球领先地位。这将使我们能够将地震的“声音”与x射线的“视觉”结合起来，从而帮助我们理解地震数据在操作规模上的意义，因为我们无法看到过程。最后，我们将研究如何将我们的观察结果与空间和时间尺度范围内的现场示例进行比较。结果将决定我们是否可以在规划阶段（通过选择不太敏感的地点）和操作期间（通过连续监测和控制）将连续监测的速度变化和响应应力扰动的其他地震特性添加到我们的武库中，以量化风险。

This project addresses the current imperative to move to a net zero carbon economy. Many practical solutions involve engineering of the ground beneath our feet, for example through geothermal energy production, radioactive waste disposal, and subsurface storage of carbon dioxide or hydrogen. The problem is that these activities add new stresses to underground reservoirs or storage sites already suffering from ambient stresses due to plate tectonics. Hence, there is a risk of even small additional stress triggering earthquakes, potentially leading to damage or nuisance from ground motion and/or allowing harmful fluids to escape to the surface, and hence losing public confidence in such solutions. For example, the onshore fracking industry in the UK triggered earthquakes as large as magnitude 2.9 in Lancashire, despite the introduction of a 'traffic light system' to manage the risk. The UK traffic light system operated to modify operations at a threshold magnitudes of 0.5 (amber) or to stop them for the day at magnitude 1.0 (red). The failure to prevent the magnitude 2.9 earthquake resulted in a moratorium on the fracking industry to the present day. It would be tragic if a similar fate awaited the net zero solutions involving engineering of the sub-surface. Here we will address the problem: can we do better? One of the main barriers to developing an effective risk management strategy is that we often do not know how close the Earth is to failure on the scale of the engineered system - are we 'on the edge' of failure (or not)? The susceptibility to small stress perturbations in the Earth is highly variable, and one of the biggest 'known unknowns' in this field. Here we will carry out a series of experiments to understand the processes involved in the triggering of fracture and earthquakes at different starting stresses, to see if we can characterise this sensitivity before we start operations, and to control the risk of extreme events during operations better than the current traffic light system. We will use new methods of accurately measuring seismic wave velocity changes that are sensitive to stress changes, and use these, and other attributes of the induced seismicity such as event rate, fault or fracture type, and the amount of associated deformation, to see if we can do better in a controlled environment. We will construct a scale model system in the laboratory, where we can mimic field conditions in terms of stress and fluid pressure. While we are deforming the rock by changing stress or pore pressure, we will record tiny micro-earthquakes caused by damage in the form of micro-cracking, and monitor changes in seismic velocity and fluid permeability. In particular, we are interested in tiny but detectable velocity transients (step changes followed by a gradual decay) associated with very small stress perturbations. Transients are thought to be caused by the sudden induced damage and subsequent slower healing of the material when stresses change. They have been observed in a variety of settings in the Earth, but their causes remain enigmatic. Here we will conduct the live experiments in a synchrotron, so we can 'see' the actual processes of deformation at the pore scale. We will build a unique, purpose-built portable deformation rig to maintain the UK global lead in this type of work. This will allow us to combine seismic 'sound' with x-ray 'vision', and hence help us understand the meaning of seismic data on the operational scale, where we cannot see the processes. Finally, we will examine how our observations compare with field examples on a range of scales in space and time. The results will determine whether we could add continuously monitored velocity change, and other seismic properties in response to stress perturbation to our armoury in quantifying the risk at the planning stage (by choosing less sensitive sites) and during operations (through continuous monitoring and control).