Explosive Seismic Effects
The effects of seismic activity resulting from an explosion are often known collectively as ‘explosive seismic effects’. However, this term covers a wide range of phenomena, varying in severity and characteristic, depending on the type of explosion and the properties of the medium in which it is detonated. An explosion that is both powerful and close to the surface can create a rapid expansion of ground materials and cause the ground to shake forcibly, creating a damaging tremor.
These explosive seismic effects involve the rapid expansion of a shockwave through the ground, leading to the release of seismic energy as elastic waves. The most widely recognised form of seismic energy generated is P-waves. These involve a sudden outward force on the ground (such as compressing, pushing, and pulling in different directions), causing it to vibrate and accumulate energy until it is released as a seismic wave.
The release of the P-wave shocks is generally accompanied by the release of S-waves. S-waves are created when the ground response has reached the point of failure, with all accumulated energy released as the ground moves along a fault line, shaking the surrounding area. Both P- and S-waves are able to cause destruction, albeit in different ways.
Not all explosive seismic effects are necessarily damaging. For example, the explosion of ammonium nitrate, used in mining operations, can be relatively harmless, as much of the energy generated is reflected back into the air. However, when powerful explosives, such as TNT, are used, the effects can be much more destructive.
The destruction caused by an explosion’s seismic activity is frequently related to the structural strength of the ground. Softer substrates, such as sand and gravel, are generally more vulnerable to destruction from seismic activity than harder substrates, such as rock or cement. This is in addition to the proximity of the surface to the explosive burst—whereby the closer and more powerful the explosion, the more destruction that may be caused.
Damage caused by explosive seismic effects range from short-term ground-shaking to more serious, longer-term destruction, such as thermo-mechanical spalling (the displacement of rock and soil particles). The intensity of such destruction varies depending on the duration and strength of the explosion, as well as other factors such as the type of explosive used.
Long-term seismic effects can often be more detrimental than those effects instantaneously caused by the shockwave. For example, the displacement of debris blocks, a phenomenon known as liquefaction, can cause major destruction of roads, bridges, and buildings, leading to obliteration or severe disruption.
Explosive seismic effects can also result in fire or injury from flying debris, and in certain cases, such as during earthquakes, fires and even fatalities have been reported as a result of explosions.
In conclusion, the effects of explosive seismic activity vary in intensity and extent, depending on the properties of the medium in which the explosion takes place, the type of explosive used, and the proximity of the surface to the explosion. These effects include short-term ground-shaking, long-term destruction, the displacement of debris, fire, and the possibility of injury from flying debris.
