In defiance of repeated international warnings, North Korea has pushed ahead a third nuclear test, two months after it fired off a long-range rocket. An artificial earthquake with a magnitude of 4.9 was detected at 11:57 a.m. on Tuesday, February 12th, in Punggye-ri, Gilju County in North Korea’s North Hamgyeong Province. About two hours and 40 minutes later, the North’s state-run Korean Central News Agency confirmed that the nation carried out a nuclear test and claimed it was a success. The news agency maintained the nuclear test was conducted to protect the nation’s sovereignty in response to the U.S.’ hostile action. It also stressed that the test helped North Korea build even stronger nuclear weapons capabilities. But North Korea did not specify the exact time or place of the test. It didn’t reveal the scenes of the detonation, either. Professor Kim Geun-sik of Kyungnam University explains that the explosive power of the third nuclear test was obviously stronger than that of previous tests.

It’s true that the level of the artificial earthquake we observed this time was higher than that of the first and second nuclear tests. Clearly, North Korea’s nuclear weapons technology has been improving. It is also worrisome that North Korea started activating highly enriched uranium in 2010 so it can secure a large amount of nuclear material now. North Korea’s successful long-range missile launch late last year also shows that the nation has improved technology for a delivery system for nuclear warheads. The latest test indicates that North Korea has raised the explosive power of the nuclear warhead and that the nation is capable of deploying nuclear weapons that could pose a threat to the U.S. So, Pyongyang now has a stronger negotiations card to pressure the U.S.

Based on the magnitude of the artificial earthquake, the South Korean government estimates that the explosive power of the test was around 6 to 7 kilotons, which is equivalent to the simultaneous detonation of 7,000 tons of dynamite. The ‘Little Boy’ atomic bomb dropped over Hiroshima, Japan, at the end of World War Two was estimated to have killed up to 160,000 people and destroyed 70 percent of buildings in the city. The yield of Little Boy was 16 kilotons of TNT, which had the same effect of setting off 16,000 tons of dynamite at the same time. So, the explosive power of North Korea’s recent test is far weaker than the early-stage atomic bombs that were dropped in Hiroshima and Nagasaki some 60 years ago. But according to Professor Hwang Il-soon of the Nuclear Engineering Department at Seoul National University, it’s difficult to conclude that the recent nuclear bomb was weak by simply comparing it to an old nuclear bomb that was directly dropped from a bomber.

It is assumed that the nuclear test had an explosive yield of around 6 to 7 kilotons. If the bomb is detonated 500 meters above the ground, the flame would spread to about a 1.2- kilometer radius and destroy buildings within a 2-kilometer radius. In Seoul, about 200,000 people might die within two months. So, North Korea’s nuclear capability has reached a very dangerous level. When the U.S. conducted a test early in 1945 before the Hiroshima bombing, I think it reached that level.

The nuclear test site in Punggye-ri, Gilju County in North Hamgyeong Province, is where North Korea conducted two previous tests in 2006 and 2009. Satellite photos show that the site is surrounded by mountains higher than 1,000 meters above sea level, including Mantap Mountain with an elevation of 2,205 meters. Therefore, experts like Professor Kim say the actual explosive power could be much stronger than observed.

The estimated explosive yield is based on the earthquake reading. The Punggye-ri test site is situated in a mountainous area with a mountain standing at 2,200 meters tall. So, the detected level of earthquake from a nuclear test deep in the mountains could be lower than that of a similar test on flat ground.

In the two previous nuclear tests conducted at the Punggye-ri site, North Korea sought to raise the explosive power. Both tests were plutonium-based. To boost nuclear fission, the country has conducted more than 100 experimental high-explosive detonations. Two months ago, it successfully launched a long-range rocket that could carry a nuclear warhead. Also, there is speculation that North Korea may have detonated a device using highly-enriched uranium technology this time around. Highly-enriched uranium may lead to mass production of atomic weapons, and that’s why the international community is paying close attention to whether North Korea used this material for its latest nuclear test. Let’s hear from Professor Hwang.

North Korea has only a small amount of plutonium because it demolished a nuclear reactor designed to produce plutonium in Yongbyon. In order not to use up plutonium, Pyongyang started enriching uranium. It is still uncertain whether North Korea successfully enriched uranium. By gathering and analyzing air samples from the recent nuclear test, we can confirm if North Korea used highly-enriched uranium or plutonium. If North Korea really used highly-enriched uranium for the test, that means the country will be able to continue producing enriched uranium needed for making atomic bombs by using centrifuges in an underground facility, although it may not produce plutonium any more. A considerable amount of raw uranium is buried in North Korea, so the nation will be able to produce a large number of nuclear weapons.

The South Korean military is paying close attention to whether North Korea has actually developed technology to miniaturize and lighten warheads to mount on missiles. North Korea’s state-run Korean Central News Agency said on Tuesday that the nuclear test was conducted safely and perfectly using a smaller and lighter nuclear bomb. It also stressed that the test results, including the explosive force of the bomb, exactly conformed to the design values. But Won Se-hoon, director of the National Intelligence Service in South Korea, says it is believed that North Korea has yet to miniaturize and lighten warheads. But if that happens, North Korea could mount a nuclear warhead on an intercontinental ballistic missile that can reach the mainland U.S. And this will certainly pose a greater threat to the international community. Some speculate that North Korea will likely pressure the U.S. to engage in bilateral talks with Pyongyang by demonstrating the result of its third nuclear test, which apparently had a more powerful explosive force than the two previous tests. Actually, North Korea did elicit dialogue from the U.S. after pressing ahead with nuclear tests in 2006 and 2009 on the heels of rocket launches. But Professor Kim has a different opinion.

Unlike the first and second nuclear tests, the latest experiment seems to indicate that North Korea is re-examining its existing nuclear strategy in a comprehensive way. In the past, North Korea sought to negotiate with the U.S. first. If the negotiations didn’t work out, the North would resort to brinkmanship tactics and create tension as a means of pressuring the U.S. But this time around, North Korea is mounting a provocation recklessly even before starting negotiations with the U.S., although the second-term Obama administration has chosen people advocating dialogue for Secretary of Defense and Secretary of State. Unlike in the past, North Korea seeks to make provocations first in a strategic move. That is, Pyongyang wants to secure nuclear weapons capability as much as it can and then decide whether it will negotiate with the U.S. I think this is more serious.

So, why did North Korea choose February 12th as the date for carrying out a nuclear test? Experts explain North Korea was conscious of the U.S., since the nuclear test came just one day before Obama’s State of the Union address. It is said that North Korea also has other purposes both internally and externally.

North Korea may have considered the political schedule of the U.S., as the nuclear test was conducted a day before Obama’s State of the Union speech, the first in his second term. Also, North Korea seems to have taken political considerations to detonate another nuclear device before the Lee Myung-bak government’s term ends, that is, before the new Park Geun-hye administration is officially inaugurated. But it’s hard to say this is the decisive factor to set the date for the nuclear test. It seems that the domestic schedules, technical issues, overall test conditions and costs were taken into consideration.

Meanwhile, the international community is moving fast to respond to North Korea’s recent nuclear test. The U.N. Security Council convened an emergency meeting on Tuesday night, Korean time. Council members strongly condemned North Korea’s nuclear test and agreed to discuss additional sanctions against the North immediately. A statement was announced by Kim Sung-hwan, foreign minister of South Korea, the rotating chair of the U.N. Security Council for this month. Kim said that the Security Council shared the view on the need for significant action. The U.S. also said that North Korea’s nuclear test is a “highly provocative act” and stressed corresponding actions. The new resolution pushed by the Security Council is expected to be much stronger than previous ones.

The U.N. Security Council adopted a resolution in January in response to North Korea’s December rocket launch. At the time, it warned of “significant action” in the event of North Korea’s additional provocation. Now, the international community is expected to agree to impose even tougher sanctions on North Korea. If the new agreement does not include military options, it will likely strengthen existing economic and diplomatic sanctions as well as maritime sanctions on North Korean ships. Council members may set these measures as obligations. China agreed on U.N. Security Council resolutions against North Korea after the North’s first and second nuclear tests. To adopt another such resolution, China’s support is essential. So, the new resolution will be drafted at the level that China may agree. Beijing is likely to vote in favor of additional sanctions against Pyongyang, but it’s unclear whether China will actually join tougher, anti-North Korea sanctions.

The South Korean government has been on high alert since it detected the signs of North Korea’s nuclear test. The presidential office of Cheong Wa Dae has entered emergency mode to keep an eye on any movements of North Korea, while the military authorities are maintaining readiness posture. The military has also announced various countermeasures to secure strike capabilities, including the deployment of cruise missiles. Noting that North Korea carried out a nuclear test before the new South Korean government takes office, Professor Kim says the possibility of resuming inter-Korean dialogue is not entirely low if the Park Geun-hye government takes a forward-looking attitude.

It is possible that North Korea may engage in inter-Korean dialogue if the Park Geun-hye government takes a turnaround approach on inter-Korean ties. North Korea has never criticized Park Geun-hye by mentioning her name so far. The most important task of the next Seoul government is to manage the security risks more effectively and focus on securing a strong deterrent against North Korea’s nuclear capabilities. South Korea may have to join international sanctions on the North. But it won’t be easy to resolve the nuclear issue solely through sanctions and pressure. It’s necessary to impose sanctions on the North. But at the same time, the government needs to pursue dialogue and compromise for a solution to the nuclear issue and make various efforts to improve relations with the North. When the sanctions are lifted and the favorable mood for better inter-Korean relations is created, the government should use the improved inter-Korean ties to contribute to resolving the nuclear issue.

In the wake of North Korea’s third nuclear test, there are growing concerns about peace on the Korean Peninsula and in Northeast Asia. Now is time for the international community to collect their ideas to resolve the nuclear issue peacefully.