Earthquake - see below

Graphics and Animation by Olivier N.

An earthquake is a sudden tremor, vibration or shaking of the ground. They are a result of a sudden release of energy from underneath the earth especially at fault margins, characteristic of seismically active zones. The earth is made up of blocks referred to as plates which are in constant motion. Such movements tend to bring plates to a point of collision or sliding along along a fault plane. Some times the slide is not smooth and much energy tends to build up. When the pressure reaches a certain level, there is a sudden release of energy which sends out shock waves and hence vibrations which reach the earth's surface and lead to earthquakes. It could be violent or mild depending on the amount of energy and vibrations that are propagated. The area of energy build-up under the earth is referred to as the focus or hypocenter and the area on the earth's surface directly above the focus is called the epicenter. Areas located around the epicenter are often the worse hit during an earthquake. This is because the intensity of the vibration felt there is more. The strength of the tremor decreases as we move away from the epicenter.

Earthquakes are known to have devastating effects across the world. They lead to deaths, destruction of infrastructure and other physical phenomena like landslides, rockfalls, tsunami, destortion of landscapes etc.

The intensity of an earthquake is measured using an instrument called a seismograph. Some examples of earthquakes: Japan in March 2011 with a 9.0 magnitude, leading to a tsunami and nuclear plant explosions, Peru earthquake in 2007.