Class 8 Science

# Natural Phenomena

## Earthquake

Sudden shaking of the earth; which lasts for a very short duration is called earthquake.

### Tectonic Plates

The crust of the earth is composed of several pieces of landmass. These are called tectonic plates. The tectonic plates are in continuous motion. They keep on brushing against each other or striking each other. When a tectonic plate brushes against another or strikes another tectonic plate; it results in vibrations in the tectonic plates. These vibrations are experienced by us in the form of an earthquake.

### Seismic or Fault Zones

The boundaries of the tectonic plates are at high risk of earthquake. These boundaries are called seismic zones or fault zones. In India; Kashmir, western and central Himalayas, the whole of the north-east, Runn of Kutch, Rajasthan and Indo-Gangetic Plain are at high risk of getting hit by an earthquake. Some parts of the Deccan Plateau are under the seismic zone.

### Seismograph

Seismograph is a device which records the seismic activities. It is composed of an oscillator, writing device and a roll of paper. The writing device is attached to the oscillator. In case of an earthquake, the oscillator begins to oscillate. This creates oscillation in the writing device; which plots wave-like patterns on the paper. The wave-like pattern is then analysed by seismologist to interpret the various features of an earthquake.

### Richter Scale

The Richter Scale was developed in 1935 by Charles Richter and Beno Gutenberg of California Institute of Technology. This is a logarithmic scale which shows the intensity of an earthquake. The intensity of an earthquake is measured on a scale of zero to 10. But earthquakes of more than 9 Richter have never been reported. The magnitude of earthquake increases by 100 times when we move one point on the Richter scale. This means that an earthquake measuring 5 on Richter scale is 100 times more powerful than one measuring 4 on Richter scale.

Most of the earthquakes go unnoticed by us because they are below 4 on Richter Scale. Earthquakes which measure more than 7.5 on the Richter scale can be highly damaging.

## Dangers Due to Earthquake

An earthquake cannot cause any damage on its own. Most of the damages caused by an earthquake are because of collapse of man-made structures; like buildings, bridges, poles, etc. Sometimes, an earthquake can result in tsunami which causes large scale damage. The infamous tsunami in the Indian Ocean which came on 26th December 2004 was because of a massive earthquake near Java.

### Protection Against Earthquake:

It is impossible to predict an earthquake and hence we need to take several precautionary measures to avoid or minimize the damage which may happen because of earthquake. Some of the preventive measures are as follows:

• Buildings should be made quake proof. Engineers and architects are the experts who can give suitable advice in this regard.
• Light-weight materials should be used for making the buildings in earthquake prone areas.
• Cupboards should be fixed to the walls so that they do not fall on someone during an earthquake.
• People should be made to practice drills for earthquake. Such drills should be frequently organized in schools and at public places.
• In case of an earthquake, you should hide under a table or any other similar structure. If you are in bed, then keep a pillow over your head and do not move out of the bed. If you are in an open area, try to move away from buildings and other structures.
• Proper installation of fire-fighting equipments should be ensured in buildings. Fire due to short circuit and gas leakage is quite common during an earthquake.