Much of the skepticism surrounding North Korea’s claim that it detonated a hydrogen bomb centers on the earthquake that was generated.

An estimated explosive yield of 6.0 kilotons and a quake with a magnitude of 4.8 were detected, South Korean lawmaker Lee Cheol Woo Lee said after a briefing by the National Intelligence Service.

That was smaller than the estimated yield of 7.9 kilotons and 4.9-magnitude quake reported after a 2013 nuclear test, he said, and only a fraction of the hundreds of kilotons that a successful H-bomb test would usually yield.

Even a failed H-bomb detonation typically yields tens of kilotons, the NIS told Lee, who sits on the parliament’s intelligence committee.

A miniaturized H-bomb can trigger a weak quake, but only the U.S. and Russia have such weapons, Lee cited the NIS as saying.