Estimates of the strength of North Korea's nuclear test on Monday vary wildly. South Korea believes it equaled 6 to 7 kilotons of TNT, but Japanese experts it may have been as much as 8 to 10 kilotons.
Germany's BER, a state-run geological research institute, said on its website that the latest test was equivalent to 40 kilotons of TNT.
The South Korean Defense Ministry said it assessed the power of the nuclear test based on analysis by the Korea Institute of Geosciences and Mineral Resources (KIGAM). An ordinary earthquake is analyzed using magnitude local (ML) methods, but an artificial earthquake from a nuclear test is monitored using magnitude body (MB) methods.
Based on MB analysis, KIGAM concluded that the test triggered a 4.9 magnitude blast. Using the method of the UN Preparatory Commission for the Comprehensive Nuclear Test-Ban Treaty Organization, KIGAM therefore assessed it as equaling 7.7 to 7.8 kilotons of TNT.
In contrast, BER said it assessed the magnitude of the blast at 5.2. The institute had also offered higher readings during North Korea's first and second nuclear tests.
"If North Korea digs a bigger hole to install nuclear devices at the test site, the power of the blast could appear smaller than it actually is," said Lee Choon-geun at the Science and Technology Policy Institute. "The power of the third test could have been as high as 8 to 10 kilotons of TNT."
