The last five of Pyongyang’s six nuclear tests have all been carried out under Mount Mantap at the Punggye-ri nuclear test site in the north-west of the country.
Three small earthquakes have been detected in the immediate area since the most recent test on September 3, Pyongyang’s most powerful by far.
The first, soon after the blast, has been widely attributed to some form of cave-in, with two much weaker tremors taking place in late September and last week.
Some reports have suggested that the site may no longer be suitable for further underground nuclear testing as a result.
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.
The respected 38 North website said there could be concern about the phenomenon at Mount Mantap, with the area affected by the September 3 test potentially extending as far as 1.4 kilometres from the detonation point.
But it added: “US nuclear test history at the Nevada Test Site provides evidence that such post-test tremors are not unusual.”
The earthquakes were therefore “not surprising”, said analysts Frank Pabian and Jack Liu.
No expectations should be raised that nuclear testing at the site would be abandoned, the analysts said, pointing out the US facility was not closed until a general moratorium on nuclear testing in 1992, and Punggye-ri has two more so-far-unused tunnel complexes.
“There is no valid reason to assume that the Punggye-ri test site is unable to contain additional underground nuclear tests,” they said.
Tensions have soared in recent weeks following Pyongyang’s nuclear test as US President Trump engages in an escalating war of words with the North’s leader Kim Jong-Un.
The North’s missile and nuclear capabilities have made significant progress under Kim, who told party officials this month that the country’s atomic weapons were a “treasured sword” to protect it from aggression.