Last updated May 10, 2018 at 11:44 am
Findings set to be a ‘game changer’ for the geothermal industry
Last November’s Pohang earthquake, the most damaging in South Korea since the first seismograph was installed in 1905, was likely triggered by fluid injection at a nearby geothermal plant, two separate reports conclude.
That would make it, at Mw 5.4, the largest-known earthquake induced at an Enhanced Geothermal System (EGS) site.
Induced earthquakes have been well-established in places such as Oklahoma, but these regions involve oil and gas extraction, not geothermal activity, which had not previously been suspected of inducing quake activity much above Mw 3.4.
Large amounts of water are injected underground at EGS sites: in the case of the Pohang site, many thousands of cubic metres of water at high pressure since 2016.
In the first of two studies, researchers from three South Korean universities created a local earthquake catalogue and this, combined with analysis of data on foreshocks and aftershocks, allowed them to suggest that the quake was induced by fluid injected directly into a critically stressed subsurface fault zone.
Based on the fluid volume, they say, injected fluid volumes much smaller than predicted by theory can trigger a relatively large earthquake.
European researchers reached similar conclusions, though based on a different data set that included satellite-based information and a range of seismological observations.
The earthquake transferred static stress to larger nearby faults, they say, potentially increasing the seismic hazard in the area more broadly and making it a “game changer” for the geothermal industry worldwide.