A magnitude four-point-six quake rocked the southeastern city of Pohang early Sunday.
The Korea Meteorological Administration said the quake occurred five kilometers north-northwest of the city's Buk district at 5:03 a.m. with a depth of 14 kilometers.
The weather agency said that the latest tremor is an aftershock of the magnitude five-point-four earthquake that hit the region on November 15 of last year.
The aftershock was the strongest since the magnitude 4.3 jolt that occurred three months earlier.
The latest quake, the 84th aftershock of the main quake that hit the same region last November, was followed by six minor tremors with a magnitude of over two.
Local fire authorities received reports that four Pohang citizens suffered minor injuries from the Sunday quake. Fifteen people who were trapped in elevators were rescued in North Gyeongsang Province.