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 ROKThe center previously issued a云海官网网站 notice saying it suspected another test because the epicenter was located on the surface4 magnitude quake would be much smaller than the quakes caused by previous DPRK nuclear tests, the report saidAfter the incident, the center quickly organized seismological bureaus and geological institutions to evaluate the situation, it saidSeismologists from the Chinese Academy of Sciences and the Unive云海官网网站rsity 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 20043 magnitude quake, while the strongest, this month, resulted in a 6