SEOUL - A rare earthquake in South Korea was triggered by the country’s first experimental geothermal power plant, a team of government-commissioned experts said Wednesday.
The southeastern port city of Pohang was rattled by a 5.4-magnitude earthquake in November 2017 — the second-most-powerful tremor ever in the normally seismically stable South. The most powerful quake to date was a 5.8-magnitude tremor that struck Gyeongju, also in the southeast, in September 2016.
A seismograph near the epicenter measured peak ground acceleration equivalent to magnitude 7.4. Poor subsoil around Pohang amplified the seismic waves passing through, making the overall damage somewhat heavier than the Gyeongju earthquake.
The earthquake damaged about 2,000 private properties, the government said; 52 homes suffered severe damage and 157 had serious damage. Damage was also reported at 227 schools across the region.
Dozens of people were injured and more than 1,500 were left homeless.
A nationwide college entrance exam was postponed in an unprecedented move as authorities scrambled with recovery efforts. The College Scholastic Ability Test was delayed by a week both in order to change testing sites and to let people recover somewhat from the quake.
The yearlong government-commissioned study has pointed to the geothermal power plant as the cause.
The plant works by injecting high-pressure water deep underground to tap heat from the Earth’s crust, but the process produced micro-size seismic activity as a result, said Lee Kang-kun, who led the research.
“And as time passed, this triggered the earthquake in Pohang,” he added. “We concluded that the Pohang earthquake was a ‘triggered quake.’ It wasn’t a natural earthquake.”
Pohang residents filed a lawsuit against the government after the quake.
Following the new report’s assessment, Seoul expressed its “deep regret.”
The geothermal plant — which was temporarily suspended during the study — will be “permanently shuttered,” the trade, industry and energy ministry said in a statement.
It cost around 80 billion won ($71 million) to build and test operations began in 2016.
Unlike Japan, the Korean Peninsula rarely experiences significant quakes. Seismic activity is closely monitored to indicate whether North Korea has staged a nuclear test.