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Research Note: AI Analysis of Nuclear Tests in North Korea, Guy Kraft and Soshi Oga, 2021.
25 Estimating magnitudes of nuclear explosions [1, 6, 32, 33, 34]
This section shows explosion magnitudes of nuclear tests, as supplementary information for nuclear test activities (in addition to the AI analysis of nuclear tests introduced in the earlier sections). Here, based on “TNT equivalent,” magnitude of nuclear explosion is estimated from the information of earthquake magnitude. [1, 6, 32]
TNT equivalent is one of the methods for expressing an energy.[33, 34] It is typically used to describe the energy released in an explosion, by converting the energy released in an explosion to the equivalent amount of TNT mass. The unit of TNT equivalent is kiloton (1 kiloton is equivalent to 4.184×1012 J [joules]). TNT stands for Trinitrotoluene (one of chemical compounds).
Here, the TNT equivalent is estimated by the following equation.
mb = A + B log Y
Y：TNT Equivalent（kiloton）
mb：Body wave magnitude (Body wave magnitude is the magnitude estimated from the amplitude
value of body wave, which is one of seismic waves)
A and B are constants. For A and B, this study refers to [A=4.45, B=0.75] of Ringdal. et al (1992).[34]
A and B are the constants which can be various values, depending on the reference model. Therefore, the output value of TNT Equivalent is essentially modeldependent estimate. However, since this study only focuses on “relative difference” of explosion magnitudes among several nuclear tests, minor problems (such as the variance of constants A and B among the empirical models and the model dependency of a TNT Equivalent value) are assumed not to be problematic in this study. Furthermore, the TNT Equivalent is generally to compute the value of explosion magnitude, although it does not consider chemical aspects of a nuclear explosion.
[The estimated values of magnitude for nuclear explosions]
Shown below are the estimated values of magnitude for nuclear explosions.
In addition to the nuclear tests conducted in North Korea from 2006 to 2016, another artificial earthquake data of the 2017 event in North Korea (Magnitude 6.3, reported as a hydrogen bomb) is included in the analysis.

North Korea, Nuclear Test (2017/09/03), mb=6.3, TNT Equivalent = 292.9 kiloton

North Korea, Nuclear Test (2016/09/09), mb=5.3, TNT Equivalent = 13.6 kiloton

North Korea, Nuclear Test (2016/01/06), mb=5.1, TNT Equivalent = 7.4 kiloton

North Korea, Nuclear Test (2013/02/12), mb=5.1, TNT Equivalent = 7.4 kiloton

North Korea, Nuclear Test (2009/05/25), mb=4.7, TNT Equivalent = 2.2 kiloton

North Korea, Nuclear Test (2006/10/09), mb=4.3, TNT Equivalent = 0.6 kiloton
Figure 9~11 show the results.
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