On the edge?

该项目解决了当前转向净零碳经济的当务之急。许多实际的解决方案涉及对我们脚下的地面进行工程设计，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，这些活动给已经因板块构造而遭受环境压力的地下水库或储存点增加了新的压力。因此，即使是微小的附加应力也有可能引发地震，有可能导致地面运动造成破坏或滋扰，和/或使有害流体泄漏到地表，从而失去公众对此类解决方案的信心。例如，英国陆上水力压裂行业在兰开夏郡引发了高达2.9级的地震，尽管引入了“红绿灯系统”来管理风险。英国交通灯系统的操作是将操作修改为0.5级(琥珀色)或将其停止在1.0级(红色)的当天。未能阻止2.9级地震，导致水力压裂行业暂停至今。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，我们将解决这个问题：我们能做得更好吗？制定有效的风险管理战略的主要障碍之一是，我们往往不知道从工程系统的规模来看，地球离失败有多近--我们是否处于失败的边缘？地球对微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数之一。在这里，我们将进行一系列实验，以了解在不同起始应力下触发断裂和地震所涉及的过程，看看我们是否可以在开始操作之前表征这种敏感性，并比目前的交通灯系统更好地控制操作期间发生极端事件的风险。我们将使用对应力变化敏感的准确测量地震波速变化的新方法，并利用这些方法以及诱发地震活动的其他属性，如事故率、断层或断裂类型，以及相关的变形量，看看我们是否可以在受控环境中做得更好。我们将在实验室中建立一个比例模型系统，在那里我们可以根据应力和流体压力来模拟现场条件。当我们通过改变应力或孔压使岩石变形时，我们将以微裂缝的形式记录由损伤引起的微小地震，并监测地震速度和流体渗透率的变化。特别是，我们感兴趣的是与非常小的应力扰动相关的微小但可检测到的速度瞬变(阶跃变化后逐渐衰减)。瞬变被认为是由于应力变化时材料突然造成的损伤和随后较慢的愈合造成的。在地球上的各种环境中都观察到了它们，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’孔洞尺度上的实际变形过程。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尺度上的意义，在那里我们看不到过程。最后，我们将检验我们的观测结果如何与一系列空间和时间尺度上的现场例子进行比较。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)和在操作期间(通过连续监测和控制)在量化风险时，将连续监测的速度变化和其他响应应力扰动的地震特性添加到我们的武器库中。

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).