Explosion Seismology - Monitoring Nuclear Explosions

Seismic Discrimination - The Art of Indentifying Explosions and Earthquakes

One of the most important problems in seismic monitoring is distinguishing underground nuclear explosions from other seismic sources. If a seismic event is large, the problem of discrimination is fairly straightforward. Explosions release their energy in a very small volume and produce primarily P waves. In contrast, earthquakes represent the motion of blocks along a fault; the source dimensions are much larger for a given size than for an explosion, and earthquakes produce large S waves.

The figure to the right compares the 1998 Indian test with an earthquake of approximately the same size. (Figure produced by Christel Hennet, IRIS.) The distance between the explosion and recording station is approximately same as the distance between the earthquake and recording station. The explosion waveform is dominated by the P wave (the first arrival), while the earthquake has large S waves (and surface waves).