Updated at 1:57 a.m. on January 6
North Korea announced it had successfully detonated its first hydrogen bomb on Wednesday morning, signaling a surprising leap in nuclear weaponry for the reclusive totalitarian regime if the claim is verified.
The U.S. Geological Survey recorded a 5.1-magnitude seismic event about 11 miles from the North Korean town of Sunjibaegam in the country’s northwest. Chinese and South Korean officials immediately suspected the earthquake was artificial, according to the BBC.
Similar tremors in that area followed each of the country’s three previous nuclear-weapons tests, all of which occurred underground at the nearby Punggye-ri Nuclear Test Site. North Korea became the eighth declared nuclear-weapons state after its first test at the site in 2006; additional detonations followed in 2009 and 2013.
Each of the country’s three earlier tests detonated atomic bombs, which rely on nuclear fission to achieve their destructive purpose. Like a dropped water balloon hitting a sidewalk, atomic bombs crack open the dense atomic nuclei of large, unwieldy elements like uranium and plutonium to release tremendous amounts of energy.
Hydrogen bombs, by contrast, use nuclear fission only for their initial detonation, igniting a secondary fusion stage by compressing lighter atoms of deuterium and tritium together until they explode, like filling up a water balloon until it bursts. The chain reaction produces a far more powerful explosion than an atomic bomb.
Pyongyang dropped hints about a possible nuclear test in the weeks preceding Wednesday’s detonation. On Saturday, South Korea’s Yonhap News Agency reported on Sunday that the North could be readying for a nuclear-weapons test. The reclusive communist state also reportedly tested a submarine-based ballistic missile last month.
The first reports that North Korea might have a hydrogen bomb also emerged in the waning days of 2015. KCNA, the state broadcaster of North Korea, quoted Kim Jong-un as describing the country as “a powerful nuclear weapons state ready to detonate a self-reliant A-bomb and H-bomb to reliably defend its sovereignty and the dignity of the nation” on December 10. Nuclear experts and the White House publicly expressed doubt about Kim’s hydrogen-bomb claim at the time.
From initial data available after Wednesday’s test, some nuclear and regional experts offered skepticism about the veracity of the North’s claim and its broader significance.
South Korean officials quickly condemned the test nonetheless, describing it as a violation of multiple United Nations Security Council resolutions and hinting at possible future sanctions. Other regional leaders echoed the sentiment. “North Korea’s latest nuclear test is a grave threat against our security and we absolutely cannot allow it,” Japanese Prime Minister Shinzo Abe told reporters, according to Asahi Shinbun. The test’s impact could also be felt in Asian financial markets.
On the other side of the Pacific, the White House struck a cautious tone in its initial response to the reported nuclear test.
This story will be updated as more information becomes available.