Hydraulic fracturing of the first shale gas well at Preston New Road (PNR), Blackpool, United Kingdom, in late 2018, marked the end of a 7 yr United Kingdom‐wide moratorium on fracking. Despite a strict traffic‐light system being in place, seismic events up to ML 2.9 were induced. The ML 2.9 event was accompanied by reports of damage and was assigned European Macroseismic Scale 1998 (EMS‐98) intensity VI by the British Geological Survey. The moratorium was subsequently reinstated in late 2019. The study here presents a pseudo‐probabilistic seismic risk analysis and is applied to the larger of the induced events at PNR, in addition to hypothetical larger events. Initially, site characterization analysis is undertaken using direct and indirect methods. These analyses show low‐velocity deposits dominate the region (⁠VS30‾=227 m/s⁠). We test existing ground‐motion prediction equations using spatially dependent VS30 to determine applicability to the recorded waveform data and produce a referenced empirical model. Predicting median and 84th percentile peak ground velocity fields, we subsequently determine macroseismic intensities. Epicentral intensities of IV, IV–V, and VI–VII are predicted for the observed ML 2.9, and hypothetical ML 3.5 and 4.5 scenarios, respectively. A probabilistic analysis of damage is performed for 3500 ground‐motion realizations (⁠2.1≤ML≤4.5⁠) using the OpenQuake‐engine, with nonlinear dynamic analysis undertaken to define building fragility. Based on these analyses, the onset of cosmetic damage (DS1) in terms of median risk is observed for the ML 2.9 event. Mean modeled occurrences of DS1 and DS2 (minor structural damage), 75 and 10 instances, respectively, are consistent with reported damage (DS1:97, DS2:50). Significant occurrences (⁠median≥30 buildings) of DS2, DS3, and DS4 (minor to major structural damage) are likely for ML 3.5, 4.0, and 4.5 events, respectively. However, by comparing reported damage with modeled damage due to the ML 2.9 event and considering the fact that low macroseismic intensities (EMS‐98 <4⁠) are often not reported by the public, we conclude that the previously assigned intensity of VI is too high, with V being more appropriate.

中文翻译：

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页岩气站点地震诱发的地震危险和风险

英国布莱克浦普雷斯顿新路（PNR）的第一口页岩气井于2018年底进行了水力压裂，标志着英国长达7年的暂停压裂作业的结束。尽管建立了严格的交通信号灯系统，但仍诱发了ML 2.9级的地震事件。ML 2.9事件伴随有破坏报告，并被英国地质调查局指定为1998年欧洲宏观地震等级（EMS-98）强度VI。暂停措施随后于2019年底恢复。此处的研究提出了一种伪概率地震风险分析，除假定的较大事件外，还适用于PNR中较大的诱发事件。最初，使用直接和间接方法进行站点特征分析。这些分析表明，该地区以低速沉积物为主（⁠VS30‾ = 227 m /s⁠）。我们使用空间相关的VS30测试现有的地面运动预测方程式，以确定对记录的波形数据的适用性，并产生参考的经验模型。预测中值和第84个百分位数的峰值地面速度场，我们随后确定宏观地震烈度。分别针对观察到的ML 2.9和假设的ML 3.5和4.5情景预测了IV，IV-V和VI-VII的震中强度。使用OpenQuake引擎对3500种地面运动实现（2.1≤ML≤4.5⁠）进行了概率损坏分析，并进行了非线性动态分析来定义建筑物的脆弱性。基于这些分析，就ML 2.9事件而言，观察到以中位风险计的美容损害（DS1）的发作。DS1和DS2的平均建模发生次数（轻微结构损坏），75和10个实例，分别与报告的损坏一致（DS1：97，DS2：50）。在ML 3.5、4.0和4.5事件中，可能会发生DS2，DS3和DS4的重大事件（中位数≥30座建筑物）（轻微至重大结构破坏）。但是，通过将报告的损害与ML 2.9事件导致的模型损害进行比较，并考虑到公众通常很少报告低宏观地震烈度（EMS-98 <4⁠），我们得出结论，先前指定的VI强度也是高，V更合适。