Seismic vibrations refer to the shaking of the ground after an earthquake. This ground shaking -- or vibration -- can have very destructive consequences. Such an effect was observed in 1964 after an earthquake in Alaska. The seismic vibrations after the earthquake caused an immense amount of structural damage and the collapse of many buildings.
Amplification of Seismic Waves
Seismic vibrations have different effects in different kinds of ground. A ground that is made up of hard rock would not vibrate much, but softer ground would shake rapidly. This is called amplification of seismic waves. This effect can be understood by considering the example of gelatin on a plate. When the plate is shaken a little bit, the gelatin starts shaking rapidly. Due to this, structures such as buildings that are built on soft ground incur more damage from seismic vibrations than buildings constructed on harder ground.
If there is considerable amount of water present underground and the ground is soft, the seismic vibrations may turn the stable ground into a fluid-like material. This process is called liquefaction. Any structure built on such a ground would be destroyed as a result of liquefaction. Also, the underground pipes, such as those for sewer and water, may rise up to the surface and float.
Seiches are the rhythmic sloshings of water in lakes and reservoirs caused by seismic vibrations after an earthquake. The vibrations produce seismic waves that propagate in water reservoirs. There they produce seiches, which can be dangerous in large reservoirs. For example, in dams, they can cause severe damage to the walls and other structures underwater.
The seismic vibrations are fairly complex because the ground shakes up and down as well as sideways during these events. The amount of destruction caused by these vibrations depends not only on their intensity and duration, but also on the strength of the structures and the type of ground on which they rest.
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