Ground penetrating radar
Ground penetrating radar uses electromagnetic waves to locate objects in the ground. The radar emits electromagnetic waves into the ground where they may reflect on certain objects. The reflected waves then allow for the identification of these objects and their location. Higher frequencies correspond to shorter waves. And the shorter the wave, the smaller the buried objects that can be detected. This technology is used to identify parts of an explosions infrastructure in the ground.
Electrical conductivity measurements
There are two distinct purposes of electrical conductivity measurements during an on-site inspection. Shallow measurements, up to five metres depth, of underground electrical properties can help identify metallic objects belonging to the infrastructure of a possible nuclear explosion. Deeper measurements will lead the inspectors to identify disturbances in the underground geological structures, such as cavities or changes in the water table, which, in both cases, may result from an underground nuclear explosion.
Active seismic survey
High resolution seismic surveys are conducted to identify changes and disturbances in the underground geological structures. During passive seismic monitoring, the inspectors “listen” to the ground, in hopes of detecting minute seismic events created by the movement of the rock adjusting to the stresses caused by the explosion.
Alternatively, inspectors may use active seismic sources to create shock waves. Such a seismic source could be a hammer on a metal plate or a large vibroseis truck. The latter is a specialized vehicle that vibrates a large plate on the ground to generate shock waves. The reflected waves are then measured by a series of geophones, enabling the inspectors to establish an image of the underground geology.
During passive seismic monitoring, inspectors listen to the sound of movements in the rock; during active seismic monitoring, they use artificially created seismic waves to listen to the waves’ reflections off structures in the ground.
This technology could be used to identify and measure the effects of an underground nuclear explosion in the surrounding geological structures. Disturbances can relate to increased fracturing in the rock and its changing porosity.
Resonance seismometry measures changes of seismic tremours in the underground. This so-called micro seismic background noise changes its properties when going through different kinds of material in the ground. Such a change may be noticeable when these tremours move from rock to a void in the underground. Hence, this technique could be used to locate cavities caused by a nuclear explosion.
Drilling is the final technique employed to ascertain whether or not a nuclear explosion has taken place. This method is applied when other techniques have located a potential explosion cavity which needs to be examined for its nuclear nature.
As drilling is about obtaining samples from the site of the actual explosion and therefore carries potentially great health risks, the procedure to allow the use of this technique is rather complex.