Chapter 18 | Earthquakes | Class- 8 DAV Science Solutions

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DAV Class- 8 Earthquakes Question and Answer

Something To Know

A. Fill in the blanks.

  1. ___Foreshock ____ are the smaller earthquakes that happen in the same place before the main quake follows.
  2. The ‘high wall sea waves’, caused by underwater earthquakes are called ___Tsunami ____.
  3. Earthquake is caused by a disturbance deep inside the ____crust ___.
  4. The waves associated with the tremors caused by earthquakes are known as __seismic _____ waves.
  5. Geologists call the point of origin of earthquakes, as its _focus ______.
  6. Destructive energy of an earthquake is measured on the ___Richter ____ scale.


B. Tick () the correct option:

1. The minor quake, that might occur before the main earthquake is known as a—

Ans. Fore shock

2. A natural phenomenon, whose triggering is not associated with an earthquake is—

Ans. Flood

3. Earthquakes occur when there is a sudden release of stored up energy in earth’s— Inner core Outer core Mantle Crust

Ans. Crust

4. The various layers are marked as A, B, C and D as shown in the given figure— A B C D The correct labeling, of these layers A, B, C and D of earth, is

Ans. A-crust, B-mantle, C-outer core, D-inner core

5.The epicenter of an earthquake is— Deep under the crust of the earth In the mantle of the earth On the surface of the earth In the core of the earth

Ans. Deep under the crust of the earth

6. The magnitude of two earthquakes A and B, on the Richter Scale were 7 and 5 respectively. The strength of—

Ans. Earthquake A is 100 times that of earthquake B


C. State True or False for the following statements.

1. It is now possible to give exact predictions about the earthquakes.False
2. Earthquakes beneath the ocean floor can generate huge tidal waves.True
3. When the plates on the earth slide past each other, the energy released gives rise to waves known as seismic waves. True
4. Richter Scale is a simple linear scale. False
5. An earthquake, of magnitude 2.5 on Richter Scale, cannot be recorded on a seismometer. True
6. In highly seismic areas, it is better to have house made from mud or timber than those made by using heavy construction materials. True


D. Answer the following questions in brief.

What is an earthquake?

Ans. Sudden shaking of the earth’s surface is called earthquake.

State any three of the ‘damaging effects’ of an earthquake.

Ans. The three damaging effects of an earthquake are: • Loss of lives • Destruction of houses • Tsunami

Explain the phenomenon of production of shock waves.

Ans. The tectonic plates are locked up at their boundaries. But the plates try to keep on moving. This causes a tension to build up in the plates. When the force of moving plates overcomes this friction at the edges, all of their stored energy gets released. This causes vibrations in the plate. The vibrations create the shock waves.

In the context of an earthquake, which of the two points: the focus or the epicenter, is deep under the ground?

Ans. Focus

Name the scale used for measuring the strength of an earthquake. Write the likely magnitude of (a) a mild earthquake (b) a highly destructive earthquake on this scale.

Ans. Earthquake is measured on Richter Scale. A mild earthquake measures about 3.5 on Richter scale, while a highly destructive earthquake measures more than 8 on Richter scale.

An earthquake measures 3 on Richter Scale. (a) Would it be recorded on the seismometer. (b) Is it likely to cause much damage?

Ans. (a) Yes (b) No


E. Answer the following questions.

1. Explain in brief, the cause of an earthquake.

Ans. Earthquake is caused by the movement of tectonic plates. The friction between two plates releases energy which causes earthquake.

2. Where are the earthquakes more likely to occur?

Ans. At the boundaries of tectonic plates.

3. Mr. Sarthak is the head of a construction company. He got a contract to design and build a housing complex in an area which was under the ‘seismic zone’. State the main precautions which Mr. Sarthak’s company should take so that houses built by it are durable.

Ans. Mr. Sarthak should take following precautions: • The structure should be ‘Quake Safe’. • Fire fighting equipments should be properly installed in the building. • Safer places and exit routes must be clearly marked. • Disaster management supplies should be available ‘one hand’.

4. State the precautions, that one should take for protection during an earthquake if one is (a) inside the house (b) Outdoors.

Ans. Safety precautions inside the house: • Take shelter under a table and stay their till the shaking stops. • Stay away from tall and heavy objects. • Do not get up if you are in bed. Protect your head with pillows. • Stay indoors until shaking stops and it is safe to move outside. Safety precautions outdoors: • Go to a clear spot away from buildings, trees, bridges and overhead powerline. Drop to the ground. • Do not come out if you are in a moving vehicle. Drive slowly to a clear spot and stay inside. Come out only when the tremors stop.

5. State the main precautions that can be taken to minimize the effect of an earthquake.

Ans. Following precautions can be taken to minimize the effect of an earthquake: • Buildings should be made ‘Quake Safe’. • Stay away from damaged areas. • Look for warning of tsunami if you are living in coastal area. • Stay calm for a while. Be ready for aftershocks. • Help the injured ones. VALUE BASED QUESTIONS Rahul and Aakash are very good

Value-Based Questions

Rahul and Aakash are very good friends. When Rahul had a fever few weeks before the examinations, Aakash decided to help him up. He did not go for his badminton sessions and used this time to give Rahul all the help and information about the lessons taught in the school. Rahul’s mother observed this and remarked that the overall effect of Aakash’s timely help is in a way similar, but opposite to the multiplicative effects of the magnitudes on the Richter Scale.

1. State the values displayed by Aakash.

Ans. Care and concern for others

2. Name the quantity that is measured on the Richter Scale.

Ans. Magnitude of earthquake

3. By what factor does the quantity go up when its magnitude on the Richter Scale increases by one?

Ans. By a factor of 10

Something To Do

1.Visit an organization which provides relief to those suffering from natural disasters. Discuss the role these organizations play in determining how cities/regions prepare for and react to earthquakes. Prepare a brief report.

Ans. Do it yourself

2. On the map of the world indicate the places where tsunami is more likely to occur. Try to find out the problems faced by people living in these regions. Take the help of newspaper clippings, school library or internet sources.

Ans. Do it yourself

3. Take a slinky (2-3 cm long). Tie its one end to the wall. Hold the other end firmly in your hand. Push and pull the slinky at the same time (for this you have to move your hand in a circle). Observe carefully. What happens to the slinky? This activity will give you an idea about the seismic (circular) waves. (The surface/circular waves are the seismic waves which cause major destruction above the ground).

Ans. Do it yourself

4. Fill the crossword with suitable words on the basis of the clues given below:

Acrosss: 1.Earthquake 2.Seismic Zone 3. Seismograph 4.Focus

Down: 1. Epicenter 2. Richter Scale 3.Tsunami 4.Foreshocks

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