An earthquake is a sudden shaking or trembling of the earth which lasts for a very short time. It is caused by the disturbance deep inside the earth�s crust. The outermost layer of the earth is called the earth�s crust. This layer is not in one piece. It is fragmented. Each fragment is called a plate.

These Plates are in continuous motion. When they brush past one another, or when one plate goes under another due to collision, they cause disturbance in the earth�s crust. It is this disturbance that shows up as an earthquake on the surface of the earth.

Tremors on earth can also be caused when a volcano erupts, or when a meteor hits the earth�s surface, or when an underground explosion is carried out. However, most earthquakes are caused by the movements of the earth�s plates.

The boundaries of plates are weak zones where earthquakes are more likely to occur. These weak Zones are also known as seismic or fault Zones. In India, the areas most prone to earthquakes are Kashmir, Western and Central Himalayas, the whole of North-East, Rann of Kutch, Rajasthan, the Indo-Gangetic Plain, and some areas of Southern India. The tremors produce waves on the surface of the earth. These are called seismic waves.

Earthquake: Seismic waves and seismograph

The tremors produce waves on the surface of the earth. These are called seismic waves. These waves are recorded by an instrument called a seismograph. This instrument is simply a vibrating rod, or a Pendulum, which starts vibrating when tremors start. A pen is attached to the vibrating system.

The Pen records the seismic waves on a paper which moves under it. By studying these waves, scientists can construct a complete map of the earthquake. They can also estimate the magnitude of destruction by studying these waves.

The magnitude of an earthquake is expressed in terms of a scale called the Richter scale. Destructive earthquakes can have magnitudes higher than 7 on the Richter Scale. Both Bhuj and Kashmir Earthquakes had magnitudes greater than 7.5.

Earthquakes can cause immense damage to buildings, bridges, dams, and people. They can cause great loss to life and property. Earthquakes can also cause floods, landslides, and tsunamis. A major tsunami occurred in the Indian Ocean on 26 Dec. 2004. All the coastal areas around the Ocean suffered huge losses due to that tsunami.

Earthquake : Safety tips

We know that earthquakes cannot be predicted but they can be highly destructive and dangerous.

It is therefore necessary to be prepared all the time and take necessary measures to protect ourselves.

1. The buildings in weak Zones (seismic zones) should be designed to withstand major tremors. The use of mud or timber is better than using heavy construction materials.
2. The cupboards and shelves should be fixed to the walls, so they do not fall easily.
3. Since buildings may catch fire due to an earthquake, it is necessary that all buildings, especially tall buildings, should have firefighting equipment installed in them.
4. If you are at home during an earthquake take shelter under a table and stay there until shaking stops.
5. Stay away from tall and heavy objects that may fall on you.
6. If you are in bed, do not get up. Protect your head with a pillow.
7. If you are outdoors during an earthquake find a clear spot, away from buildings, trees, and overhead power lines, and lie down on the ground.
8. If you are in a car or a bus, do not come out. Ask the driver to drive slowly to a clear spot. Do not come out until the tremors stop.

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