Policy ForumInduced Seismicity

Managing injection-induced seismic risks

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Science  24 May 2019:
Vol. 364, Issue 6442, pp. 730-732
DOI: 10.1126/science.aax1878

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Summary

Heat transported from deep within Earth's crust can be used to generate electricity or provide direct heating by circulating fluid through permeable fracture networks in hot rock. Because naturally permeable systems are rare, enhanced geothermal system (EGS) technology stimulates the creation of permeable pathways in otherwise impermeable rock by means of the injection of water under high pressure, creating new fractures and causing preexisting fractures to open. But several EGS projects have encountered problems of induced seismicity, particularly the moment magnitude (Mw) 5.5 earthquake in 2017 that occurred near an EGS drill site in Pohang, Republic of Korea (South Korea). Here we explore the implications of, and derive lessons from, the Pohang experience. The Pohang earthquake provides unequivocal evidence that EGS stimulation can trigger large earthquakes that rupture beyond the stimulated volume and disproves the hypothesis that the maximum earthquake magnitude is governed by the volume of injected fluids. Because that hypothesis tacitly underpins hazard-based methods used for managing induced seismicity, those methods must be revised and based on considerations of risk.