A shallow 2.9-magnitude earthquake struck near North Korea's nuclear test site on Friday before dawn just weeks after Pyongyang's biggest detonation. However, the South Korean experts have said that the tremor did not appear to be man-made.
The US Geological Survey said that the tremor hit at 1.41am (12.41am, Singapore time) with a depth of around 5km. The authorities added that the epicentre of the quake was located north of the Punggye-Ri testing site.
"This event occurred in the area of the previous North Korean nuclear tests. The event has earthquake-like characteristics, however, we cannot conclusively confirm at this time the nature (natural or human-made) of the event," the US agency told AFP.
Meanwhile, the South Korea Meteorological Administration posted on its official website that "analysis shows it was a natural quake". The administration added: "It is believed to have caused no damage."
This latest tremor came three weeks after a 3.5-magnitude earthquake struck near the same area. The seismic experts and a UN nuclear test ban watchdog had referred to the tremor on September 23 as an aftershock of the North's sixth and largest nuclear test.
A stronger 6.3-magnitude quake was triggered by a test on September 3 and it was felt across the border in China and sparked global condemnation. Following the tremor, the United Nations Security Council had unanimously adopted tough new sanctions against Pyongyang.
When compared to the tremors registered during any of North Korea's previous nuclear tests, the authorities said that the strength of Friday's quake was much lower. In 2006, North Korea's first detonation triggered a 4.1-magnitude quake.
Due to the recent nuclear tests by Pyongyang, tensions have soared up and the US President Trump has been engaged in an escalating war of words with the North's leader Kim Jong-un.
In September, Trump used his maiden speech to the UN to threaten to "destroy" the nuclear-armed nation if Kim did not back down, referring to him as "Rocket Man".
In response to Trump's speech, Kim rebuked him, calling Trump "mentally deranged" and threatened the "highest level of hard-line countermeasure in history".