A three-point-six magnitude aftershock struck the southeastern city of Pohang in North Gyeongsang Province on Monday morning.
The Korea Meteorological Administration said that the shock occurred eleven kilometers north of the city's Buk district at 6:05 a.m. with a depth of 12 kilometers. 
Another aftershock with a magnitude of three-point-five hit the area about six hours earlier at 11:45 p.m. Sunday.
Monday’s quake is the second most powerful aftershock since a five-point-four magnitude earthquake rattled the city last Wednesday. The most powerful aftershock measured magnitude four-point-three and struck two hours after the initial earthquake. 
The weather agency estimated that nearly 60 aftershocks occurred as of late Monday afternoon.