Questions and Answers About North Korea’s Claims that it Detonated a Nuclear Bomb
How does one measure the size of a nuclear or hydrogen bomb explosion?
The size of any seismic event is determined from the amplitude of the waves recorded at stations of varying distance from the event. The seismic magnitude is determined independent of the source type. The absolute amplitude of arriving body waves and surfaces waves are needed to determine the size of the event. The Earth also modifies the seismic waves as they travel from the source to each receiver, so some information about Earth structure is also needed. One of the largest pieces to determining the size or yield of an explosion is the depth of the event. This key piece of information is used in converting seismic magnitude to the amount of explosive material needed to make a potential bomb.
What are the tell tale signs?
Man-made explosions are detonated very close to the Earth surface. Seismically, this means that certain seismic surface waves should be recorded and, in contrast, certain seismic “depth” phases are not likely to be present in the seismograms. Depth phases are upgoing waves that bounce off the Earth’s surface and are accurate indicators of the source event depth. In addition, explosive sources produce a different signal which is outward everywhere. This is different than earthquakes which are sliding motions on faults where motions will be different depending on where the observation is made.
When will experts be able to confirm what actually happened?
As soon as possible. Ok, the seismic component of the forensics is probably the most straightforward. All the seismic data are in-hand and agencies are working on the determining the depth of the event to better estimate the yield (kilotons). The noble gas and radionuclide airborne detectors will be the most key in determining the exact nature of the explosion, whether it is really a thermonuclear event or not. This analysis should be complete within a few days. Other news agencies have been reporting that some countries will be doing air surveys to collect more data. In the end, it’s likely that no single agency will possess all the available data on this event. Each country and agency determines what happened based on the information they have available. Not everybody shares well.
If it wasn’t a hydrogen bomb, what was it?
The explosion measures [5.1] on the Richter scale, that is the equivalent of about 10 kilotons of TNT (smaller than the atomic bomb dropped on Hiroshima during WWII). The seismic impact of a Hydrogen bomb likely would be much bigger, so there is legitimate doubt about what actually took place. It’s possible the bomb tested was relatively small, failed, or that the explosion was created with chemical explosives, or conventional atomic bomb. It’s difficult to say what type of bomb it was from the seismic signal and more in-depth analysis of potential radionuclides that escaped from the blast could tell.
How many seismic events around the world raise legitimate concern of nuclear or hydrogen explosion on a yearly basis? Is this number rising or falling or staying constant?
There have been well upwards of 2,000 nuclear explosions recorded since 1945. North Korea is believed to have detonated nuclear bombs in four separate tests since 2006. Other nations are believed to be building or maintaining undisclosed nuclear programs like North Korea’s, but the number of measureable tests associated with these programs is irregular.