*Seismologists at Columbia University’s Lamont-Doherty Earth Observatory show North Korea’s latest test detonations—especially the second on Friday, Feb. 12, 2013, Eastern time, local afternoon in Korea—were larger in explosive power than the 2006 test. In terms of energy released, Friday’s blast registered about the equivalent of 6 to 7 kilotons of TNT. The 2006 test was estimated at 3 to 4 kilotons.*

Scientists at Columbia University’s Lamont-Doherty Earth Observatory are reporting that North Korea’s latest nuclear explosions, especially the second on Friday, Feb. 12, 2013, Eastern time, local afternoon in Korea, were larger in explosive power than the 2006 test. In terms of energy released, Friday’s blast registered about the equivalent of 6 to 7 kilotons of TNT. The 2006 test was estimated at 3 to 4 kilotons.

Paul G. Richards, Lamont Research Professor and head of the seismology lab at Lamont-Doherty, and research scientist Won-Young Kim measured seismic signals from the February 12 explosions at five seismic monitoring stations operated by the Chinese Earthquake Administration in the far northeastern part of China, about 200 kilometers (125 miles) from the reported test site in North Korea’s mountainous northeast.

“We looked at high-frequency seismic waves that travel through the Earth’s crust and can be readily recorded at relatively short distances,” said Richards. “From these we estimated magnitudes. Then, using previously published empirical data relating magnitude to explosive energy yields for contained explosions, we determined that the second test was about twice as powerful as the first.”

The scientists posted their results on Saturday, February 16, in an online article on the respected scientific news site Eos (Transactions, American Geophysical Union). Friday’s larger blast was a clear violation of the Comprehensive Nuclear-Test-Ban Treaty of 1996, prohibiting all nuclear explosions in any environment—though the treaty has not yet entered formally into force, pending ratification by all signatories.

Although the seismic signals were recorded clearly at the Chinese monitoring stations, Richards said that the exact nature of the device exploded under North Korea’s heavily monitored Mount Mantap remained unclear, as did its design and whether it was fission-based (like an atom bomb) or thermonuclear (like a hydrogen bomb).

“The seismic signatures suggest the use of a new, more powerful device than in 2006, but we cannot say much beyond that,” he said. “These are all contained underground tests, so there are no radioactive aerosols released into the atmosphere.”