Haenam hit by 11th earthquake since mid-September as fault activity suspected

A magnitude-2.6 earthquake struck 21 kilometers west-northwest of Haenam-gun in South Jeolla Province at 10:30 a.m. Saturday, the Korea Meteorological Administration said.

The epicenter was located at 34.66 degrees north latitude and 126.40 degrees east longitude, at a depth of 20 kilometers, according to the Korea Meteorological Administration.

The latest tremor is part of a series that began in the area with a magnitude-2.1 quake on Sept. 14, followed by a magnitude-2.5 on Sept. 15, magnitudes of 2.2 and 2.4 on Sept. 16, a magnitude-2.3 on Sept. 21 and a magnitude-2.7 on Sept. 22.

Particularly notable was a magnitude-3.1 earthquake that struck the same area on Sunday, which produced maximum seismic intensity of 4 — strong enough to be felt — across South Jeolla Province and Gwangju.

Further quakes of magnitude 2.5, 2.1 and 2.2 followed on Tuesday, Wednesday and Friday, respectively, before Saturday's magnitude-2.6 event. In total, 11 earthquakes of magnitude 2.0 or greater have struck the Haenam area since Sept. 14.

The Korea Meteorological Administration urged residents near the epicenter to stay alert, saying they may feel the ground shaking.

Seismologists refer to repeated earthquakes of similar magnitude occurring in a confined area over a short period as a "swarm earthquake." The Korea Institute of Geoscience and Mineral Resources (KIGAM) previously analyzed a similar swarm in the Haenam area and concluded that the tremors originated from left-lateral strike-slip movement along a deep fault system running west-northwest to east-southeast beneath the epicenter zone. Left-lateral strike-slip movement refers to horizontal displacement of the crust on either side of a fault plane. KIGAM noted that this fault cluster is a relatively small-scale fault zone distinct from the nearby Gwangju Fault, a major structural lineament in the region.

Experts increasingly believe an active fault may exist beneath the Haenam area. Woo Nam-cheol, a senior seismic analyst at the Korea Meteorological Administration, said active faults have generally been found wherever earthquake swarms have been observed. Kim Kwang-hee, a professor in the Department of Geological Sciences at Pusan National University, pointed to records in the Annals of the Joseon Dynasty showing that an earthquake near Jindo in 1436 occurred in roughly the same location as the current Haenam swarm. "The fact that earthquakes have recurred in the same area roughly 500 years apart suggests that an ancient fault went through a long dormant period before being reactivated," Kim said.

However, experts consider it unlikely that the current cluster of small earthquakes will directly trigger a major event. Son Moon, a professor at Pusan National University, said the magnitudes recorded so far do not point to a high probability of a strong earthquake following. KIGAM similarly concluded in its earlier analysis that the likelihood of a large earthquake remains low. In expert discussions involving Kang Tae-seop, a professor at Pukyong National University, and others, several factors were cited: the epicenters are clustered within a narrow zone of roughly 500 meters; past swarms off Boryeong in 2013 and near Baengnyeongdo in 2019 did not lead to major earthquakes; and the focal depth of 20 kilometers means much of the seismic energy dissipates before reaching the surface.

Experts caution that the Korean Peninsula cannot be considered free from seismic risk simply because it lies away from tectonic plate boundaries. Jeong Yong-bok, head of the National Territory Safety Research Division at KIGAM, said in a media interview that while the peninsula is sometimes perceived as relatively safe because it does not sit on a plate boundary, it is in fact an intraplate region where active faults are distributed. The peninsula sits at the intersection of multiple tectonic forces: compressional stress from the collision of the Indian and Eurasian plates to the west, stress generated by the subduction of the Pacific Plate into the Japan Trench to the east, and long-term stress from the Philippine Sea Plate to the south. The accumulation of these stresses along pre-existing faults is considered the primary mechanism behind earthquakes on the Korean Peninsula.

The 2016 Gyeongju earthquake (magnitude 5.8) and the 2017 Pohang earthquake (magnitude 5.4) are widely cited as examples of faults that were not clearly visible at the surface but ruptured under accumulated stress. These events have led researchers to raise ongoing concerns about the possible existence of blind faults — those undetectable at the surface — and to call for detailed geophysical surveys of fault zones in the Yeongnam region, including the Yangsan Fault system. While the prevailing view holds that the current Haenam swarm is unlikely to trigger an immediate large earthquake, the Korea Meteorological Administration and KIGAM said they will continue monitoring seismic activity in the area and conducting detailed analysis.