Earthquake is a sudden and violent shaking of the ground, sometimes causing great destruction, as a result of movements within the earth’s crust or volcanic action. In other words you can define earthquake as a sudden movement of the earth’s crust caused by the release of stress accumulated along geologic faults or by volcanic activity.
Earthquakes cause many different kinds of damage depending on:
- The magnitude of the earthquake—in general, the larger the quake, the stronger the shaking and the larger the area affected.
- The distance from the earthquake—the closer to the source of the earthquake, the greater the shaking.
- The type of ground material beneath the structure—soils may amplify or deamplify the shaking relative to hard bedrock. and
- the building construction.
- Level of development of particular country
A given Richter reading will produce vastly different amounts of damage in different parts of the world. Even the same quake can have very different effects in neighboring areas. Many areas much closer to the quake suffered only minimal damage.
The combination of uncompacted soil with a lot of water in it led to a phenomenon called liquefaction. Liquefaction occurs when the ground loses its cohesion and behaves like a liquid. When this happens during an earthquake it can result in increased intensity of the shaking, or landslides. It can also cause collapse of buildings. Another factor that has a major effect on the damage is the building method and materials used. Unreinforced masonry has the worst record since it has little ability to flex or move without collapsing. Wood frame buildings, or reinforced buildings, on the other hand, can hold together under quite severe shaking