"A sound wave, which is usually generated in the event of an artificial earthquake, was not detectedThe China Earthquake Administration, of which the CENC is a bb电子斗大网址part, and related departments conducted studies on the infrasonic records of the earthquake and previous quakes including those provoked by nuclear tests on the Korean PeninsulaEarlier, South Korea's weather agency said the quake is presumed to have been a natural one, the country's Yonhap news agency reportedThey concluded that Saturday's quake is a natural one, the seismic service said4 on the Richter scale that occurred Saturday in the Democratic People's Republic of Korea (bb电子斗大网址DPRK) is not the result of a nuclear test, the China Earthquake Networks Center (CENC) said"The quake is presumed to have occurred naturally," the report quoted an agency official as saying