"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 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 Peninsula美高美官方网站Earlier, 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 美高美官方网站Saturday in the Democratic People's Republic of Korea (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