The US Geological Survey (USGS) has reported that aftershocks are still being felt from North Korea's huge nuclear test in September, adding that the country's politically provocative test had moved the Earth's crust.
Two small tremors, of magnitude 2.4 and 2.9, were detected between and 1am and 2am EST last week according to the USGS and Lassina Zerbo, executive secretary of the Comprehensive Nuclear-Test-Ban Treaty Organisation.
In a tweet, Zerbo called the aftershocks "unprecedented for the region" and said that analysts had confirmed they were tectonic in origin.
The aftershocks were detected in the vicinity of the Punggye-ri nuclear test site in the north-east of the country.
"They're probably relaxation events from the sixth nuclear test," said a USGS official (via Global News).
"When you have a large nuclear test, it moves the Earth's crust around the area, and it takes a while for it to fully subside. We've had a few of them since the sixth nuclear test."
North Korea's underground test, conducted on 3 September, was its sixth and largest to date. Pyongyang claimed at the time it was testing an H-bomb experts believed to be 10-times more powerful than the bomb the US dropped on Hiroshima to end the Second World War in 1945.
The test was first noticed when a quake registering at magnitude 6.3 was detected from the region.
"The H-bomb test was carried out to examine and confirm the accuracy and credibility of the power control technology, and internal structural design newly introduced into manufacturing the H-bomb to be placed as the payload of the ICBM," the state mouthpiece Korean Central News Agency (KCNA) said at the time.
According to South Korea the sixth test was 9.8 times more powerful than the fifth and 11 times strong than the fourth.
The test sparked outrage around the world, with further sanctions imposed on North Korea by the United Nations. South Korea fired ballistic missiles in a live-fire drill shortly after the test, while US president Donald Trump called North Korea a "rogue nation" on Twitter.