Abstract
A damaging Mw5.5 earthquake occurred at Pohang, South Korea, in 2017, after stimulating an enhanced geothermal system by borehole fluid injections. The earthquake was likely triggered by these operations. Current approaches for predicting maximum induced earthquake magnitude ({M}_{max }) consider the volume of the injected fluid as the main controlling factor. However, these approaches are unsuccessful in predicting earthquakes, such as the Pohang one. Here we analyse the case histories of induced earthquakes, and find that {M}_{max } scales with the logarithm of the elapsed time from the beginning of the fluid injection to the earthquake occurrence. This is also the case for the Pohang Earthquake. Its significant probability was predictable. These results validate an alternative to predicting {M}_{max }. It is to monitor the exceedance probability of an assumed {M}_{max } in real time by monitoring the seismogenic index, a quantity that characterizes the intensity of the fluid-induced seismicity per unit injected volume.
Highlights
A damaging Mw5.5 earthquake occurred at Pohang, South Korea, in 2017, after stimulating an enhanced geothermal system by borehole fluid injections
The ability to accurately predict the expected maximum possible magnitude, Mmax, of a potential artificially triggered earthquake is a critical question that arises during fluid-related geotechnical operations[1,2,3], such as water reservoir, artificial lake construction and underground waste- and saltwater disposal[1,4,5,6,7,8], enhanced geothermal system (EGS) development[2,9,10,11,12], hydrocarbon production[13,14], CO2 capture, sequestration and underground gas storage[15], hydraulic fracturing of rocks[16,17], and coal, mineral, and ore mining[1]
In November 2017 near the city of Pohang, South Korea, shortly after borehole fluid-injection operations targeted to a stimulation of an EGS, an unexpectedly strong earthquake occurred
Summary
A damaging Mw5.5 earthquake occurred at Pohang, South Korea, in 2017, after stimulating an enhanced geothermal system by borehole fluid injections. A direct application of the seismogenic index model[23,30,31] to the largest earthquake in a time series of fluid-induced seismicity has provided an estimate[24] of Mmax.
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