Extrapolation of populations of small earthquakes to predict consequences of low- probability high impact events: The Pohang case study revisited

The magnitude (MW) 5.5 Pohang, Korea, earthquake on 15 November 2017, induced by the Pohang Engineered Geothermal Systems (EGS) project, caused one fatality and ?US$300 million of economic consequences. Commission, appointed Korean Government to investigate this earthquake, has made public a release data including magnitudes smaller earthquakes associated with well stimulations. On basis population, it been proposed that significant probability such losses was predictable beforehand, project should have suspended, implying its developer remiss for not doing so. This argument depends low b-value estimated, ?0.61. However, three factors are shown contribute, individually or in combination, inaccuracy these determinations: recording bandwidth permanent seismograph stations area; miscalibration formula determining local Korea; relation used estimate events from larger template matching. These all cause underestimation smallest documented, resulting b-values. true b-values higher, being 1.12 August 2017 stimulation PX-1; similar values estimated other A consequence analysis is any as large MW = 5.5, predicted ahead occurrence extrapolation using b-values, much lower than claimed. highlights need agreed workflow specifications reporting datasets like this, where might influence prosecution EGS developers, acceptable risk arising projects.