The most damaging earthquake since South Korea started monitoring seismic events over a century ago was likely caused by a geothermal plant using a technique similar to hydraulic fracturing, according to scientists.
Geothermal energy, which is used for heat or to produce electricity, is a hot topic right now. It is renewable like wind and solar, but unlike those options, it isn’t intermittent, meaning it can be used any time we like, 24/7. It also has a relatively small land-footprint, unlike hydroelectricity.
One of the challenges it faces, though, is that conventional utility-scale geothermal systems require discovery of hot aquifers deep below the surface, often in seismically active regions and areas at some distance from the population centres that need the energy.
But the geography that geothermal can service can be significantly expanded if instead of exploiting hot aquifers, high-pressure water is injected into hot crust and then returned to the surface for clean energy purposes. This technique, known as enhanced geothermal systems (EGS) is similar to hydraulic fracturing, or fracking, used to extract shale gas, but without the mix of additional chemicals in the water that is used by the natural gas industry. In addition, unlike fracking, the injected water is pumped back up, so it is not supposed to increase pressure deep underground.
However, two separate papers appearing in the journal Science this week have linked a $38-million pilot EGS plant in Pohang, South Korea, to the most damaging earthquake in the country since instrumental seismic observation began in 1905.
Last November, the earthquake, registered as a 5.4 magnitude event, hit the city that is home to some 520,000 residents. The region is not a tectonic hotspot and has no history of significant quakes. No one was killed, but 90 people were injured, older buildings fell down and roads and walls were damaged.
A team of South Korean seismologists had set up a network of eight sensors in Pohang prior to the quake. In their paper, they conclude that a number of foreshocks started beneath the EGS injection well. A second team of European researchers employing regional seismic data independently concluded that the proximity of the quake origin to the EGS site suggests that it was human-caused. The latter team also found that the earthquake had in turn transferred stress to larger nearby faults, and thus may have boosted the seismic hazard of the area as a whole.
British Columbia has long been touted as an excellent location for the development of such clean energy due to the province’s world-class geothermal resources. BC Hydro has identified 16 possible geothermal sites in the province. All the prospective sites however employ conventional geothermal systems rather than EGS, either seeking out hot aquifers or re-using old oil and gas wells.
It is also worth keeping in mind that EGS is very much a technology that is still under development. Natural Resources Canada believes the technique may have potential to be “an important matrix of energy supply” over the long term, and a comparative modelling analysis has been performed on nine sites in Quebec. But the ministry has since concluded that moving from the modelling stage to a pilot project is “hardly conceivable at present” due to the costs.
The Climate Examiner speaks to one of North America’s leading seismicity experts on geothermal energy, the history of enhanced geothermal systems and the 2017 South Korean quake.