Subterranean tremors caused by an experimental geothermal plant may have triggered South Korea’s second-worst earthquake in its history.
This is according to a government-commissioned study of the November 2017 disaster in the city of Pohang, when a 5.4 magnitude quake crumbled the city and injured dozens of people. The study concluded that activity at a geothermal plant, which injects water underground to stimulate thermal energy production, likely caused the disaster.
“A series of micro-sized earthquakes occurred when fluids were injected by excavating a geothermal well at the geothermal power plant, which eventually triggered the Pohang earthquake,” Lee Kang-keun of Seoul National University, who co-led the study, told The Korea Times on Wednesday.
“We use the word ‘trigger,’ as the earthquake occurred beyond the scope of stimulated area,” Lee added. “It was not a natural earthquake.”
Two studies published to Nature in 2018 strongly suggested that a geothermal plant was to blame for the destructive earthquake.
The first, conducted by South Korean researchers found that “the Pohang earthquake was induced by fluid from an enhanced geothermal system (EGS) site,” the magnitude of which “makes it the largest known induced earthquake at an EGS site.”
A second study by a team of international researchers concluded that, based on “local seismometer network, well logs, satellite observations, teleseismic waveform analysis, and stress modeling leads,” the Pohang quake was “almost certainly” anthropogenically induced.
“If the Pohang earthquake is really induced, it’s a kind of game-changer in the hydro-geothermal power plant industry,” Jin-Han Ree, a structural geologist at Korea University in Seoul and lead author of one of the studies, told Nature News at the time.
As noted by Nature News, the type of geothermal plant in Pohang was notable for extracting thermal power from “less-ideal locations,” and that at least some seismic activity is to be expected.
Such geothermal systems work by creating subsurface fractures deep underground that water will permeate through injection wells. The earth’s crust heats this water, which then returns to the surface to power a turbine and generate electricity. An EGS fact sheet produced by the US Department of Energy claimed that any resulting seismicity events “are of such low magnitude that they are not felt at the surface.”
By now, geothermal fluid injection is known to cause earthquakes—such as the 3.4 magnitude quake that hit Basel, Switzerland in 2006, damaging the city’s buildings and infrastructure. And the fear now looms over communities living near geothermal outfits in the United States.
The South Korean government will be permanently suspending the plant, reported South Korean broadcaster KBS World Radio News. The government will also spend 226 billion won (roughly $200 billion USD) over five years to repair damage in parts of Pohang that were hit hardest by the quake.