A natural earthquake of magnitude 2.5 occurred on Saturday near North Korea's nuclear test site, the fourth such tremor since the North's most recent atomic explosion there, South Korean officials said.
The micro-quake occurred about 2.7 kilometers northeast of the Punggye-ri nuclear site in the country's north-eastern province of North Hamgyong, the Korea Meteorological Administration said on its website.
"The quake is a natural one and it is believed to have occurred in the aftermath of the sixth nuclear test", it said.
Minor tremors have been detected after the North carried out its sixth and most powerful nuclear test underground in September, damaging geological structures in the area, it added.
Monitors at that time said the nuclear test created an artificial 6.3-magnitude earthquake at the testing site, which South Korean experts said was nearly 10 times more powerful than the 10-kiloton test carried out a year earlier.
North Korea's nuclear test site may be suffering from the geological condition "Tired Mountain Syndrome" following the latest atomic blast, but it is unlikely to be abandoned, according to the website 38 North.
Tired Mountain Syndrome is a name for the effect of below-ground nuclear blasts on the surrounding rock, which is extensively fractured and becomes increasingly permeable.