North Korea's nuclear test on Monday might have been a "mini-nuke" explosion possibly as low as one kiloton, comparable to some small tests by India and Pakistan in 1998, scientists said on Monday.
The U.S. Geological Survey said it had detected a 4.2 magnitude quake in North Korea at 10:35 local time (0135 GMT) on Monday, confirming a similar report from South Korea.
Gary Gibson, senior seismologist at Australia's Seismology Research Center, said a 4.2 magnitude quake would be the result of a one kiloton explosion.
"It depends on how the thing is set off. There is not a perfect correlation between magnitude and the yield and depends to some extent on the rock type they set it off in," he said.
"It is a relatively small nuclear test."
A U.S. intelligence source agreed that a preliminary examination of the data did not indicate a large blast or a series of explosions. But the source stressed that analysts were still working toward a definitive evaluation.
Nuclear analyst Andrew Davies, from the Australian Strategic Policy Institute, said if the North Korean test yield was only a kiloton, Pyongyang may be disappointed.
"A kiloton is a very low yield and would tend to suggest, I would have thought, that the device was not all they hoped it would be," Davies told Reuters.
"If a nuclear, plutonium bomb fizzles, you can still get one or two kilotons quite easily. You still get a significant energy release. But an efficient device will give you more like 20 (kilotons)."
A source in Beijing who is close to the North Korean regime said Pyongyang had detonated a neutron bomb, designed to release larger amounts of deadly radiation than other nuclear weapons. There was no immediate confirmation of the claim.
Neutron bomb? That doesn't sound right...
