Some experts suggested the area is now too unstable to conduct more bomb tests.
The magnitude 2.7 quake occurred about 54 kilometers northwest of Kilju, the town where the test site is located in northeastern North Korea, according to officials at South Korea's Korea Meteorological Administration. They said it wasn't man-made and didn't appear to cause any damage in the area.
The officials, who requested anonymity citing department rules, said they believe the four quakes probably happened because the underground nuclear test on September 3 weakened or affected the tectonic plate structures in the area.
The region isn't one where earthquakes naturally occur and no quakes were detected after the five smaller nuclear tests North Korea has conducted since 2006.
The officials declined to say how the recent quakes might have affected the area and the test site, where all of North Korea's nuclear bomb tests have taken place. But some civilian experts said North Korea may stop using the site.
North Korea, which is accelerating its efforts to develop more powerful nuclear weapons and missiles, is unlikely to waste its limited nuclear materials by conducting tests that are weaker than its sixth.
But a more powerful underground detonation at the current site could be "potentially suicidal," not only because of the weakened ground, but also because of the threat of a volcanic eruption at Mount Paektu, which is about 100 kilometers away, according to Kune Yull Suh, a professor of nuclear engineering at Seoul National University.
Du Hyeogn Cha, a visiting scholar at Seoul's Asan Institute for Policy Studies, previously expressed similar worries, saying he wondered whether North Korea would be able to carry out another nuclear test in the area.
Other experts said the quakes might have been caused by landslides or the collapsing of test structures such as tunnels.
North Korea's state media haven't reported any of the four quakes detected by South Korea and other countries.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)