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(LEAD) N. Korea's latest nuclear test 11.8 times more powerful than fourth blast: weather agency

All Headlines 16:42 September 03, 2017

(ATTN: UPDATES with details, background)

SEOUL, Sept. 3 (Yonhap) -- North Korea's latest nuclear test is believed to be 11.8 times more powerful than its fourth blast in January last year in terms of the magnitude of the tremors caused by the blasts, South Korea's state weather agency said Sunday.

Earlier in the day, an artificial quake happened around the North's Punggye-ri nuclear test site. The North later confirmed the blast, saying it successfully tested a hydrogen bomb designed to fit on an intercontinental ballistic missile.

According to the Korea Meteorological Administration, the quake's magnitude was measured at 5.7, the most powerful yet, compared to 5.0 in the fifth test in September last year and 4.8 in the fourth test in January last year.

Officials said that a 0.2 increase in magnitude usually means the energy released from a nuclear test is two times more powerful than before. In that sense, the latest test was five to six times more powerful than last September's fifth test and 11.8 times more powerful than the fourth test, they said.

Weather agency officials cautioned that the assessment could be different from the actual yield of the bomb. But a government official, who spoke on condition of anonymity, said that the yield of Sunday's test is estimated at about 50 kilotons, which is equal to that of 50,000 tons of TNT.

"Today's artificial quake in North Korea was detected at all 150 quake monitoring centers across the country," Lee Mi-sun, a KMA official, said during a briefing. "Comparing seismic waves with those of the past .... we've determined that it's certainly an artificial quake."

The quake was centered about 200 meters north of the North's Punggye-ri nuclear test site.

It was the regime's sixth nuclear test. The previous tests took place in 2006, 2009, 2013 and twice last year.

Tremors from the explosion were also felt across South Korea.

According to the National Emergency Management Agency, a total of 31 quake reports have been filed with fire stations across the country, with 13 reports in Seoul, nine in Gyeonggi Province, four in Incheon, three in Gangwon Province, and one each in the North Chungcheong and South Chungcheong provinces.

Of the 13 reports received in Seoul, 10 came during the 9 minutes between 12:29 p.m., when the quake happened, and 12:38 p.m., when the KMA confirmed the artificial quake in the North, officials said.

"We've received reports that things were shaking," a fire official said. "Since the KMA's announcement, we've been telling people that it's because of a quake in the North."

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