A 4.1 magnitude earthquake struck off the southeastern city of Pohang on Sunday, but there have been no reports of damage, meteorological officials said.
The quake happened at 12:53 p.m. in waters 50 kilometers northeast of the port city at a depth of 21 km, officials at the Korea Meteorological Administration said.
The KMA had earlier announced the quake's magnitude was 4.0 but later revised it.
About 1 1/2 hours later, a smaller 2.5 magnitude quake happened at 2:12 p.m. in waters 45 km northeast of Pohang at a depth of 21 km. The KMA has determined that the second quake was an aftershock of the earlier quake.
"This is a quake-prone region, but the magnitude is larger than usual," a KMA official said. "We're trying to check if there is any damage, but there have been no reports of damage received so far as the location is about 50 km off the coast."
The official also said the quake is unlikely to cause a tsunami as its magnitude is less than 6.0
"This is not believed to be related to the 2017 quake in Pohang, but an additional examination is necessary," the official said, referring to a series of powerful quakes with magnitudes of up to 5.4 that damaged more than 2,000 homes and buildings in the city and left dozens of people injured and more than 1,000 displaced from their homes.
Tremors from Sunday's quake were felt across the southeastern region, with dozens of 119 emergency calls reporting vibrations, including 10 calls in North Gyeongsang Province, 10 in South Gyeongsang Province and six in the city of Ulsan.
It was the first time that a quake with a magnitude of 4.0 or more has occurred in South Korea since a 4.6 magnitude quake happened in Pohang on Feb. 11 last year. (Yonhap)