Chinese scientists say the 3.4 magnitude earthquake recorded on Saturday near the Democratic People’s Republic of Korea’s most recent nuclear test site was “natural”.

“The incident was not a nuclear explosion, but had the characteristics of a natural quake,” the China Earthquake Networks Center said late on Saturday in a statement released online.

Seismologists from the Chinese Academy of Sciences and the University of California Santa Cruz also published a joint report on Saturday that said tests had shown the quake “clearly falls in the natural phenomena category” and was similar to the last natural earthquake in the region, which was recorded in December 2004.

A 3.4 magnitude quake would be much smaller than the quakes caused by previous DPRK nuclear tests, the report said. The weakest generated a 4.3 magnitude quake, while the strongest, coming this month, resulted in a 6.3 magnitude quake.

“Saturday’s earthquake is likely a lagged, imploded earthquake” potentially caused by a delayed collapse of tunnels or upper land structures affected by an earlier nuclear detonation, according to the joint report.

The earthquake rattled the area of Kilju in northeastern DPRK, about 6 kilometers from the Punggye-ri facility where the country held its last nuclear test.

The Republic of Korea’s weather agency also assessed the quake as natural, The Associated Press reported on Sunday.

The report said the analysis of seismic waves and the lack of sound waves clearly showed the quake was not caused by an artificial explosion, citing an unnamed weather agency official from the ROK.