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Updated: 25 Jan 2011

181 countries have signed on.

Why is it taking us so long?
What was your knee-jerk reaction?

Fear was our gut reaction. We fear that the treaty would open the door for cheating while preventing non-cheaters from improving their arsenals.

Meanwhile, A lame-duck democratic Congress ratified the START treaty on 22 Dec 2010. Congratulations to Obama and the Congress for enabling a new path toward a safer world.

Can nuclear tests be detected?

Nothing is foolproof at the sensing limit--heating is possible if nuclear weapon testing cannot be detectable reliably. However, modern detection ability is now so sensitive and so widely dispersed, that in the practical military sense, cheating has become impossible anywhere on earth.

The rest of this page addresses the reliability of sensing nuclear-weapon testing with respect to the detection limits, which vary a bit geographically. The world is in fact now quite safe from clandestine nuclear testing going undetected. Read on.

Current Means For Detecting Nuclear Explosions

  • Direct Means (Evidentiary)

    • Seismic Stations
    • Radionuclide Stations
    • Hydroacoustic Stations
    • Communications intercepts
    • Satellite Sensing un-natural earth disturbance

  • Indirect Means (Circumstantial)

    • Satellite Surveillance of excavation, road, and complex building.
    • Political Behavior
    • Mining, imports, exports, shipping activities

Our focus from here is mainly on the direct means for sensing nuclear testing.


    Since Eisenhower’s day, an astonishing amount has been learned. Among other conclusions to be drawn is that cheating has become impossible in any practical and real sense. Explosions of two kilotons can be reliably detected. What is more, they can be sorted out from earth quakes and other natural seismic events, such as volcanic eruptions. Smaller explosions are of little or no military value.

    Detection means exist in a variety of patterns. Nuclear explosions occur at point sources; compressive waves result and dominate the seismic signature. Earth quakes are caused by lateral movement of two blocks of earth in shear; shear waves result. Shear waves travel faster through the earth and arrive at seismographs sooner than do compression waves. The greater the time lapse in their arrival times at a seismograph, the more distant they are. Three or more seismographs detecting the same event can unambiguously pinpoint the location of the source. The relative magnitudes of the two waves differ enough to distinguish shear events from the compressive types.

    A meteor impact might be indistinguishable from a nuclear explosion by seismic signature but its location and verifiability by other means can rule out any nuclear origin. So also for mine collapse. In that case there is a distinctive difference in signature. Say a mine collapse occurs in Northern Pakistan, where Al Qa’ida hangs out. The seismic wave that first arrives at a seismograph in compression/rarefaction mode is rarefaction (decompression; the rock comes loose and falls before it hits the floor in compression). For a nuclear explosion, the first seismic wave to arrive in that mode is compressive. In a nuclear explosion, pressure in all directions occurs instantly. For the slower mine collapse, there is a time lapse between rock loosening and its hitting the floor, and that is the signature of a collapse. Any such Pakistan event having such a signature would therefore be ignored.

    Of course, sensitivity of a seismograph depends on it distance from the event. That issue is resolved in two ways: Locating hundreds of seismographs on all continents in strategic locations, and increasing their innate sensitivity. Their ultimate sensitivities are limited by the natural background of “noise” produced by winds, waves, human activities, and earth creaking from earth tides induced by the gravitational fields of the moon and sun. So areas away from big cities, shore lines, or other areas such as active volcanoes are most useful for weapons-testing surveillance by seismographs.

    While is is also true that seismographs cannot be located just anywhere and everywhere, their locations and reach are more than adequate to catch cheaters anywhere.

    For example:

    Region Kilotons Detectable
    Europe 0.04
    Middle East 0.08
    North America 0.08-0.20
    South America 0.20-0.30
    Russia 0.08
    Africa 0.08-0.20
    Australia 0.20

    To put this into perspective, 0.04 kilotons is equivalent equivalent to 80 lbs, about 36 KG, of dynamite. Mines and earth-moving projects employ these amount routinely. 0.2 kilotons is a yield of 400 lbs, about 180Kg, of dynamite. The perspective here is that these sensitivities are high enough to detect any military-useful level of nuclear explosion. Mine explosions are discounted daily by the detection system. It is getting plenty of practice.

    As for the reliability of sensing at the detection limit, 95% is the convention. Seismic false positives still yield locations that can be checked by other means. Satellite and radioactive sensors can be backed up by ground inspection if a treaty exists.

    This brings us the the weapon-modernization question. The fact here is that all nuclear powers know the amount of fuel it takes to constitute a nuclear device. Modernizing igniting devices is not prohibited. So where is the problem? Well there is another one. Because it is radioac tive, nuclear material ages. That means it deteriorates slowly, loses explosive strength, and ignition ability. This impairs reliability. Re-refining military-grade material to levels known-to-work requires maintaining processing facilities subject to inspection or and other sensing means.

    As for the delivery systems, they too are detectable. So also for any actual missile launch, intentional or not.


    This technique covers the ocean basins and backs up seismic sensing. Again, vast technical improvements have bee made since the advent of the Cold War. While these devices are limited to their own sea basins and see extraneous noise, they have significant verification value when earth quakes occur at sea. Earth quakes are not point sources and therefore produce acoustic signatures differing considerably from those arising from point sources.

Communications intercepts

    This technique is as old as civilization itself. Technology for scrambling communications is far advanced. But when a leak occurs, it is evidentiary. The cat-and-mouse game gives the edge to the most advanced in the state of the communication arts.

Leaking Radiation

    Here too technology has advanced dramatically since Eisenhower’s day. As a matter of fact, the device exploded deep under ground by North Korea, was detected and confirmed in Canada as soon as the prevailing winds permitted. The evidence was ironclad in that the type of device exploded was identified.

Satellite Sensing Un-natural Earth Disturbance

    Here too, the world is in good shape. Nuclear craters are readily and directly identifiable. Buried deeply, nuclear tests do not leave craters. But satellite photography is so good, that it can not only detect buildings, roads, waste dumps, but even the shaft itself. For sure, all this can be hidden to a degree, but to the extent is is not, it is direct evidence. In the case where seismic sensing indicates an event--look at that spot.

See member states for the signatories of the treaty, CTBT for elements and locations of sensing technologies, and Scientific American for a popular rendition. Our take is that by signing on, the US has far more to gain than to lose. We are in a period where the real battles are over ideas as much as for battlefield dominance. The latter has not served us well. It is time to move on to new ideas. Our signing the CTBT should enhance that effort.

Because times change, and upon taking office new information comes his way, a new president cannot be expected to keep all of his campaign promises. Nevertheless, although CTBT is still unratified, Obama has moved toward that eventuality by signing the START treaty with Russia--after an historic Senate ratification vote of approval, 71-26. I is expected to take formal effect on 5 Feb 2011 with a ceremony in Munich. The selection of Munich for the signing could hardly be more fitting.

Obama stated before taking office:

“As president, I will reach out to the Senate to secure ratification of the CTBT at the earliest practical date and will then launch a diplomatic effort to bring on board other states whose ratifications are required for the treaty to enter into force.”

Barack Obama, 10 Sept 2008.

Thank You, Barack, for progressing toward your stated goal. Because of this move on the part of both nuclear super powers, the world will be safer. A less important aside is that now, you have won your Nobel Peace Prize spurs beyond that award's citation.

We are in new times. Terrorism has become a game changer. New tactics and strategies alike are needed. Ironically, it has motivated the nuclear powers to see the obvious. WMDs in the hands of terrorists can hardly be allowed, regardless of political, economic, or religious persuasions. The ultimate terror begets the ultimate fear and creates bedfellows of the petty and noble, Left and Right, theist and atheist, rich and poor, and any other grouping except perhaps terror groups themselves. It's about time this issue became something we can each work toward by finding common ground in Dialogue.

See: The Tipping Point is this regard.

In spite of earlier US resistance to the CTBT, 337 facilities (see full text) are now in place to sense nuclear testing and report back to head quarters.

For updates see: CTBTO.

For the latest on the Russian Arsenal, see:
Russian Strategic Nuclear Forces
and for estimates of the US arsenal see:
US Nuclear Arsenal.


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