In November 2017, a 5.5-magnitude earthquake struck the southeast coast of South Korea, injuring 90 people and causing an estimated $52 million worth of damage to buildings, homes, and infrastructure.
Curiously, the region is far from any active fault lines, leading to speculations that the nearby Pohang enhanced geothermal power plant was somehow to blame – after all, natural gas extraction through hydraulic fracking has been tied to an alarming increase in seismic activity in several US states, and South Korea appeared to be following that pattern. Since pumping operations began at the plant, one previous major earthquake and several hundred smaller earthquakes had occurred, yet the ground had been more or less stable for decades beforehand.
This proposal was met with initial debate, however, by a subset of skeptical local geologists, who argued that the link was tenuous due to the fact that no steam injections had been performed for two months prior to the Pohang event. Some countered instead that plate shifts in continuously active nearby areas, such as Japan, were transferring movement to Korea.
Yet now, five months later, two separate studies published in Science implicate the geothermal plant using a wealth of evidence. A geothermal power plant in Iceland. Wikimedia Commons
In the first investigation, a South Korean team led by Pusan National University revealed their analysis of data collected from seismic sensors that had been serendipitously placed around the site’s two fracking wells just five days before the Earthquake.
Lead author Kwang-Hee Kim and his colleagues determined that the high-magnitude quake originated directly below the plant’s 4-kilometer-deep (2.5-mile-deep) well, an area of rock that was already under high tension due to an undiscovered subsurface fault. They conclude that highly pressured water, pushed into fractures in the mantle by recent injections, triggered the fault to slip, resulting in “the largest known induced earthquake at an EGS [enhanced geothermal system] site”.
The second paper, undertaken by a European research team, pulled data from a different set of regional seismological sensors and reviewed satellite images showing how the surface of the ground around Pohang shifted after the earthquake.
“It would be a very a remarkable coincidence if this earthquake were to be unrelated to the activity at the site, given that it occurred so close to it,” co-author Robert Westaway, a senior research fellow at the University of Glasgow's school of engineering, told The Guardian. “My own personal view is that it is highly likely there is a connection.”
Sadly, though fracking has been undeniably confirmed to provoke seismic activity, how to prevent such a disastrous side effect will require significant future research. According to Westaway, the risk of earthquakes was previously thought to go up depending on the amount of water injected, yet the Pohang plant had used relatively small volumes compared to other EGS plants. Furthermore, even though no steam injections had been performed in two years, a 4.6-magnitude earthquake occurred in February of 2018.
