Not all nuclear arms are created equal. They have four main designs that progressively raise the destructive power of the weapons and their ability to obliterate large targets. The biggest are known as city busters.

Despite that range of fiery outcomes, and the unthinkable consequences, nuclear experts say that unusually large test explosions can be achieved in a variety of ways, making the field of atomic forensics quite difficult for distant experts.

With Sunday’s large North Korean blast, Norsar, short for the Norwegian Seismic Array, a research group based in Kjeller, noted that global shock waves alone provide insufficient information to determine if the detonation was a true hydrogen bomb, as the North declared.

“But we can say in general,” the group added, “that the credibility of the claim increases with increasing explosive yield.” It said other evidence, such as leaks of radioactivity from the underground test site, might solve the riddle of the bomb type in the weeks to come.