An official of South Korea's Meteorological Agency said acoustic waves should be detected in the event of a man-made natural disaster.
On Friday, Donald Trump called the North Korean leader Kim Jong Un a "madman", a day after which Kim dubbed him a "mentally deranged USA dotard" who would face the "highest level of hard-line countermeasure in history".
Terming North Korea's latest violation of the relevant UN Security Council resolutions as a source of deep regret, the spokeswoman said, "We are convinced that now it is more important than ever before for all parties involved to stop escalating tensions that are accompanying every new round of reactions and counter reactions".
The agency said it was analysing the nature of the quake and its initial view was that it was a natural tremor because no sound waves specific to man-made earthquakes were detected.
"North Korea's weapons program is a grave threat to the Asia-Pacific region and the entire worldwide community".
President Trump has accused China of not putting enough pressure on Kim's regime to step back from its sabre-rattling.
Tensions between the USA and North Korea have been escalating this year over Pyongyang's nuclear weapons ambitions.
President Trump announced Thursday he signed a new order to help the US target people, companies and banks financing and facilitating trade with North Korea.
President Trump had also called North Korean leader Kim Jong Un "a madman" who doesn't mind starving or killing his people'.
"It could be a natural quake that really was man-made as the nuclear test would have transferred a lot of stress", he said.
North Korea has launched dozens of missiles this year, several flying over Japan, as it accelerates its program aimed at enabling it to target the United States with a nuclear-tipped missile. "S. dotard with fire".
"None other than Trump himself is on a suicide mission", Ri said in broad denunciation of Trump that brought applause from the North Korean delegation.
The mission in global airspace on Saturday was said to show how seriously President Donald Trump takes North Korea's "reckless behavior".
Sunday, Trump responded to Ri's United Nations speech with another threat, tweeting that if Ri "echoes thoughts of Little Rocket Man, they won't be around much longer!"
North Korea has been working on developing missiles that can reach the United States and its allies and pair them with a miniaturized nuclear warheads.
President Trump had recently ordered fresh sanctions over Pyongyang's weapons programmes and even praised China for taking an action to limit financial transactions with North Korea. It would ban exports of liquefied natural gas to the North immediately as well.