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An official at the Korea Meteorological Administration in Seoul surveys data on the earthquake that occurred east-southeast of Gyeongju in North Gyeongsang Province at 4:55 am on Nov. 30. (Yonhap)

A shallow, magnitude 4.0 earthquake hit the city of Gyeongju in North Gyeongsang Province at 4:55 am on Thursday. It was the second biggest quake Korea has seen this year, following a 4.5 magnitude quake that occurred 52 km off the coast of Donghae, Gangwon Province, on May 15. The Gyeongju quake is the biggest to strike on land in Korea this year.

As the quake occurred not too far from the city’s Wolsong nuclear power plant, critics of nuclear power are becoming more vocal about safety concerns. Many are calling for the immediate decommissioning of aging nuclear power plants at a time when operators are trying to extend their lifespans.

Gyeongju saw a much larger quake of 5.8 magnitude in September 2016, the largest to be recorded in the area, but the recent quake’s epicenter was a mere 10.1 km away from the Wolsong nuclear plant, while the 2016 quake’s epicenter was 27 km away from the plant.

The Nuclear Safety and Security Commission (NSSC) has declared that the recent Gyeongju quake posed no real safety threats to the Wolsong plant. The plant’s seismographic systems measured 0.0421 g (“g” is a unit denoting gravitational acceleration at Earth’s surface). The plant’s design plans state that the system can tolerate an acceleration of up to 0.2 g, which could represent an earthquake of 6.5 magnitude. Reports confirm that on-site safety inspections of the plant have revealed no safety concerns.

Yet none of these safety claims negate the possibility of a quake of 6.5 magnitude or larger, one that exceeds the 0.2 g seismic design threshold, occurring in the region. A study published by the Ministry of the Interior and Safety on faults in the southeastern region (North and South Gyeongsang provinces, Busan, Ulsan) revealed 14 active faults that have the potential to produce an earthquake of 6.5 magnitude or larger. The study was published in early 2023. Based on earthquake magnitude and proximity, five of these 14 faults were judged to have the potential to affect the structural integrity of the Wolsong plant. These faults are referred to as “faults for consideration in seismic design.”

Among the 16 nuclear plants operating in regions along the southeastern coast, only Shinkori nuclear power plants unit Nos. 3-6, which were built relatively recently, were designed to withstand an earthquake of 6.5 magnitude or larger (0.3 g).

Joint Action of Gyeongju Citizens Opposing Nuclear Power, a local anti-nuclear power activist group, released a statement that opposes attempts to extend the lifespan of the already aging Wolsong power plant.

“The Wolsong nuclear power plant’s construction was based on faulty inspections of the geological integrity of the ground and surrounding region. Its earthquake-resistance designs are subpar, and today’s earthquake only magnifies our concerns about the plant’s safety,” the statement said.

“The South Korean government must begin the processing of shutting down Wolsong power plant units 2,3 and 4, as they are exposed to the risks of active faults,” the statement continued.

The Interior and Safety Ministry raised the Central Disaster and Safety Countermeasures Headquarters’ emergency level to Level 1 on the day of the quake at 5:05 am, and set its alert level at “caution.” No incidents of death or injury were reported as of 11 am on the same day.

By Kim Jeong-su, senior staff writer; Son Ji-min, staff reporter

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