Concepts

Class 8
Chapter 15 Class 8 - Some Natural Phenomena

The power of an earthquake is expressed in terms of a magnitude on a scale called the Richter scale.

It is measured in Richter scale.

It is measured with the help of instrument called seismograph

If the power of an earthquake is more than 7 on the Richter scale, it is dangerous

Note

Richter scale is not linear

If 2 earthquakes measure 4 and 6 on the richter scale,it does not mean that second earthquake is 1.5 times first earthquake

It actually means that it is 1000 times the first earthquake

## Seismograph

It is an equipment used to measure seismic waves of an earthquake

It has a vibrating rod or pendulum which is attached to a pen

During an earthquake,when earth vibrates,the pen records vibration on a piece of paper

Explanation

When earth vibrates, the vibrating rod of the seismograph starts vibrating.

The pen attached to the vibrating rod 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 its power to cause destruction.

The working of a seismograph can be seen in this video

## How to Make buildings “Quake Safe”?

To make buildings earthquake safe, we should

• In Highly seismic areas,use mud and timber as building material inplace of cement
• Cupboards should be attached to walls so that they do not fall
• Wall clock,photo frames etc should be hanged where they do not fall on people in case of earthquake
• Hire Qualified Architects,Engineers for advice while making buildings
• Since some buildings may catch fire due to an earthquake, it is necessary that all buildings have fire fighting equipment in working order.

## Questions

NCERT Question 6 - Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?

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