Reliable Earthquake Magnitudes for Induced Seismicity (REMIS)

英国鲍兰页岩蕴藏着约1300万亿立方英尺的页岩气，这是一种未来几十年价值数千亿英镑的可开采资源。如果要开采这种资源，必须使用水力压裂(水力压裂)，即在高压下向岩石中注入液体，以形成裂缝，天然气可以通过裂缝流动。这一过程将美国转变为天然气出口国，并大幅降低了全球天然气价格。然而，在这一过程中会产生危险：水力压裂以及采矿、碳捕获和储存可能会引发地震，如果地震足够大，可能会导致地球表面的震动，从而导致破坏。为了减轻这类地震对人们和基础设施的风险，监管机构要求，如果交通灯系统发生一定震级以上的地震，就必须停止运营。然而，现有的用于表征地震的方法没有考虑到可能的震级范围，这意味着将会有基于地震参数估计的随机变化或偏差而错误地允许操作继续(或被停止)的情况。“假警报”将导致数百万英镑的收入损失，而意外地震事件造成的损失也将同样高昂--甚至还不知道这些结果中的哪一种更有可能是由于地震震级的误差造成的。最近的研究表明，事件地点的误差可能是所述不确定性的数倍，直接影响地震震级估计。在这个以技术为主导的方案中，我们提出了一种新的方法，通过使用地表一组地震仪的记录，在不同衰减的情况下，联合估计地下地震速度和观测到的微震的位置。这种安排在成本和速度方面是有利的，尽管受到地震和台站之间地下属性的不确定性的限制。这种完全非线性的方法首次允许计算地震参数和地下属性之间的真实权衡，得出事件发生在特定位置和特定震级以上的真实联合概率。我们将把该方法应用于几个现有的数据集。其中一次是2011年5月在兰开夏郡Preese Hall发生的2.3级地震，它暂停了水力压裂测试，也是对未来可能发生的事情的直接记录。另一个是在诺丁汉郡的新奥利顿煤矿记录的一组采矿引发的事件，作为英国未来工业部署的极好模拟。我们还将测试我们对玻利维亚和埃塞俄比亚三座火山下岩浆室的成像能力，使用我们应用于现有数据的方法。通过将我们的结果与现有方法的结果进行比较，我们将显示传统技术中存在偏见的地方。我们的方法已经以多种方式得到验证，将作为有用的基本事实，我们可以将不完全考虑地下速度和事件震级的关联分布的方法与之进行比较。这项提议的总体目标是开发一种新的方法，以更好地成像地球，并能够创建关于地球过程和结构的具体的、可验证的假说。然而，一个配对的、完整的目标是设计新的建议，以改善对英国和世界各地未来诱发地震活动的监测和高价值决策。我们将利用我们所描述的工作包的结果，为未来的交通信号灯监控系统构建具体的、概率的阈值，并使监管机构、运营商和公众受益。

The Bowland Shale, England, contains ~1,300 trillion cubic feet of shale gas, a recoverable resource worth hundreds of billions of pounds over coming decades. If this resource is exploited, it must be done so using hydraulic fracturing ('hydrofracturing'), where fluids are injected at high pressure into the rocks to create fractures through which the gas can move. This process has transformed the USA into a gas exporter and dramatically reduced prices worldwide. Nevertheless, hazards arise from this process: hydrofracturing, alongside mining and carbon capture and storage, may induce earthquakes, which if large enough, can cause shaking at the Earth's surface that leads to damage. To mitigate the risk of such earthquakes to people and infrastructure, regulators demand that operations halt if earthquakes above a certain magnitude occur in a 'traffic light' system. However, existing methods used to characterise earthquakes do not account for the possible range of magnitudes, meaning that there will be cases where operations are incorrectly permitted to continue (or are halted) based on random variation or bias in the earthquake parameter estimates. 'False alarms' would lead to millions of pounds of lost income whilst damage from unexpected seismic events would be equally costly-and it is not even known which of these outcomes is rendered more likely by errors in earthquake magnitudes. Recent work shows that errors in event locations may be many times the stated uncertainties, directly impacting earthquake magnitude estimates. More broadly, earthquake magnitudes and locations estimated routinely by geological surveys worldwide suffer from similar trade-offs.In this technology-led proposal, we propose a new method to estimate jointly the seismic velocities of the subsurface and the locations of observed microearthquakes while varying attenuation, by using recordings from an array of seismometers at the surface. Such an arrangement is advantageous for cost and speed purposes, though is limited by uncertainty in the properties of the subsurface between the earthquakes and the stations. This fully non-linearised approach allows for the first time to calculate true tradeoffs between earthquake parameters and subsurface properties, yielding true joint probabilities that an event occurs in a certain location, and above a certain magnitude.We will apply the method to several existing datasets. One contains the magnitude 2.3 event at Preese Hall, Lancashire, which halted the testing of hydraulic fracturing in May 2011, and so is a direct recording of what might be expected in future. Another is a set of mining-induced events which were recorded at the New Ollerton coal mine in Nottinghamshire, and serves as an excellent analogue for future industrial deployments in the UK.We will also test our ability to image magma chambers beneath three volcanoes, in Bolivia and Ethiopia, using our method applied to available data. By comparing our results to those from existing methods, we will show where bias is present in traditional techniques. Our method, having been validated in several ways, will serve as a useful ground truth against which we may compare methods which do not fully account for the linked distribution of subsurface velocities and event magnitude.The overarching objective of this proposal is to develop a new method to better image the Earth and enable the creating of specific, testable hypotheses of Earth processes and structure. However, a paired, integral objective is to devise new recommendations to improve monitoring and high-value decision-making for the future of induced seismicity in the UK and worldwide. We will use the results of the work packages we describe to construct specific, probabilistic thresholds for future 'traffic light' monitoring systems, and benefit regulators, operators and the public.