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Extrapolation of microearthquake populations to predict consequences of low- 3 probability high impact events: the Pohang case study revisited 4 5
  • Rob Westaway
Rob Westaway
University of Glasgow, University of Glasgow

Corresponding Author:robert.westaway@glasgow.ac.uk

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The November 2017 magnitude (MW) 5.5 Pohang, Korea, earthquake, induced by an Engineered 24 Geothermal Systems (EGS) project, caused one fatality and ~US$300M of economic 25 consequences. It has been proposed that a significant probability of such losses was predictable 26 beforehand, from the small earthquakes caused by well-stimulation, so the project should have 27 been suspended, implying that its developer was remiss for not doing so. This argument depends 28 on the low (~0.61) estimated b-value of this earthquake population. However, it is shown that 29 many of the magnitude determinations are inaccurate (underestimated) and the true b-value is 30 higher (1.12 for one subset). The probability of any earthquake as large as MW=5.5, predicted 31 beforehand by extrapolation, was thus much lower than has been claimed. This analysis 32 highlights the necessity of taking care over accuracy when reporting datasets like this, especially 33 in situations where such analyses might influence criminal trials of EGS developers.