Many years ago, I managed to convince VERTIC’s then Executive Director, Michael Crowley, to send me on a two day trip to Vienna just to meet with our friends at the Comprehensive Nuclear Test Ban Treaty Organization. During those days, the treaty’s verification regime was still half built, and the building was buzzing with activity. The Public Information Section of the organization’s Legal and External Relations Division, then headed by Ambassador Daniela Rozgonova, invited me on a grand tour of the building.
One meeting in particular stand out from those days. I met with a member of the International Monitoring System Division, who took me through how the system works. He started off with this brilliant presentation – a slideshow that I really think should be placed on the CTBTO website – which made everything perfectly clear. I realized that for all its complexity, the verification regime is actually based on simple assumptions. There was a clean beauty hidden in its simplicity. There was also something remarkably touching to see ancient earth science techniques mated with the latest in 21st century processing, analysis and communication.
Now anyone can get that experience. The CTBTO has recently started a new course on the treaty and its verification regime. It covers the verification system, of course, but also offers more, much more. It may be too late to apply to the present round, but those interested in a similar experience may want to contact the Secretariat to inquire about the next round.
And don’t despair if you cannot get there in person. It’s all going to be streamed. Live.
Civilian scientists claim they can detect and identify all technologically significant nuclear underground tests. USIC experts always had doubts and their position seems to prevail in the US and be one of the reasons this country doesn’t ratify the CTBT.
Is it possible to hide underground tests or make them look like earthquakes?
It’s said there are several seismic characteristics distinguishing underground tests from earthquakes:
* Magnitude of about 4 or higher (unless it’s a micronuke or fizzle)
* Shallow depth (few hundred meters instead of several kilometers)
* High shear to pressure wave ratio (S/P ratio)
* A sudden onset (no pre-tremors)
* Presence of Raleigh waves (kind of very long range surface wave)
* The “focal mechanism” model which summarizes all seismic data is different
A detonation inside a large air filled cavity is known to attenuate seismic signals by 1-2 magnitudes. This is less surprising if we note that only about 0.5% of the explosion energy is usually converted into radiated seismic energy. Since almost all energy is absorbed it makes sense that different conditions may significantly vary the residue converted to seismic signals.
Detection of surface waves requires being close to the focus (less than 1500km). Such data may be often unavailable to the international community.
What about the other signs? It may sound like science fiction but seismic signs can be manipulated in principle.
An earthquake hypocenter (focus) depth is determined by the lag of reflected surface waves behind the body waves. Suppose an underground test is conducted on an island in the middle of a large deep marsh. The deep mud ring will block (decouple) the original surface waves and a well timed conventional explosion performed outside it may be mistakenly interpreted as the reflected surface waves of the main blast, misleading depth measurements and causing gross over-estimation of the hypocenter depth. If depth is computed to be more than a few kilometers a natural origin is automatically assumed. Note that the secondary explosion need not be very strong if performed in a high coupling area (i.e. rocky hills).
The calculated seismic moment may be about a magnitude lower than the measured body waves but a calculated depth of say 10 km will be more convincing.
The Raleigh waves will be also blocked by the deep mud ring. A well planned chain of pre-blast conventional explosions may mask the sudden onset, if needed. A sophisticated design of the blast chamber could possibly reduce the S/P ratio, e.g. if it’s shaped like an horizontally “S” letter. Another way to produce more shear waves is to detonate two devices inside two parallel horizontal tunnels near the opposite ends.
Could a complete and correct “focal mechanism” produced with such methods? Probably not, but seismologists have to work sometimes with partial data and since they deal with complex systems they allow error margins. A reasonable imitation of a natural focal mechanism may be acceptable, especially if the culprit is considered “nice”. You can’t conduct a detailed investigation for every medium sized seismic event.
All this may seem like a wild speculation but there is good reason to think it actually happened. The scientific community should be on the lookout for novel monitoring evasion scenarios.