The DAV Class 8 Science Solutions and DAV Class 8 Science Chapter 18 Question Answer – Earthquakes are essential study tools for DAV public school students in Class 8.
DAV Class 8 Science Ch 18 Question Answer – Earthquakes
DAV Class 8 Science Ch 18 Solutions – Earthquakes
Something To Know
A. Fill in the blanks:
Question 1.
________ are the smaller earthquakes that happen in the same place before the main quake follows.
Answer:
Foreshock
Question 2.
The ‘high wall sea waves’, caused by underwater earthquakes are called ________ .
Answer:
Tsunami
Question 3.
Earthquake is caused by a disturbance deep inside the ________ .
Answer:
crust
Question 4.
The waves associated with the tremors caused by earthquakes are known as ________ waves.
Answer:
seismic
Question 5.
Geologists call the point of origin of earthquakes, as its ________ .
Answer:
focus
Question 6.
Destructive energy of an earthquake is measured on the ________ scale.
Answer:
Richter
B. Tick (✓) the correct option:
Question 1.
The minor quake, that might occur before the main earthquake is known as a-
(a) Major shock
(b) After shock
(c) Main shock
(d) Fore shock
Answer:
(d) Fore shock
Question 2.
A natural phenomenon, whose triggering is not associated with an earthquake is-
(a) Tsunami
(b) Landslide
(c) Flood
(d) Eruption of volcano
Answer:
(c) Flood
Question 3.
Earthquakes occur when there is a sudden release of stored up energy in earth’s-
(a) Inner core
(b) Outer core
(c) Mantle
(d) Crust
Answer:
(d) Crust
Question 4.
The various layers are marked as A, B, C and D as shown in the given figure-
The correct labeling, of these layers A, B, C and D of earth, is
(a) A-crust, B-outer core, C-mantle, D-inner core
(b) A-outer core, B-crust, C-mantle, D-inner core
(c) A-crust, B-mantle, C-outer core, D-inner core
(d) A-outer core, B-mantle, C-crust, D-inner core
Answer:
(c) A-crust, B-mantle, C-outer core, D-inner core
Question 5.
The epicenter of an earthquake is-
(a) Deep under the crust of the earth
(b) In the mantle of the earth
(c) On the surface of the earth
(d) In the core of the earth
Answer:
(a) Deep under the crust of the earth
Question 6.
The magnitude of two earthquakes A and B, on the Richter Scale were 7 and 5 respectively. The strength of-
(a) Earthquake A is 100 times that of earthquake B
(b) Earthquake A is 10 times that of earthquake B
(c) Earthquake A is 2 times that of earthquake B
(d) Earthquake A is 1/10 times that of earthquake B
Answer:
(a) 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.
Answer:
False
2. Earthquakes beneath the ocean floor can generate huge tidal waves.
Answer:
True
3. When the plates on the earth slide past each other, the energy released gives rise to waves known as seismic waves.
Answer:
True
4. Richter Scale is a simple linear scale.
Answer:
False
5. An earthquake, of magnitude 2.5 on Richter Scale, cannot be recorded on a seismometer.
Answer:
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.
Answer:
True
D. Answer the following questions in brief:
Question 1.
What is an earthquake?
Answer:
Sudden shaking of the earth’s surface is called earthquake.
Question 2.
State any three of the ‘damaging effects’ of an earthquake.
Answer:
The three damaging effects of an earthquake are:
- Loss of lives
- Destruction of houses
- Tsunami
Question 3.
Explain the phenomenon of production of shock waves.
Answer:
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.
Question 4.
In the context of an earthquake, which of the two points: the focus or the epicenter, is deep under the ground?
Answer:
Focus
Question 5.
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.
Answer:
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.
Question 6.
An earthquake measures 3 on Richter Scale.
(a) Would it be recorded on the seismometer.
(b) Is it likely to cause much damage?
Answer:
(a) Yes
(b) No
E. Answer the following questions:
Question 1.
Explain in brief, the cause of an earthquake.
Answer:
Earthquake is caused by the movement of tectonic plates. The friction between two plates releases energy which causes earthquake.
Question 2.
Where are the earthquakes more likely to occur?
Answer:
At the boundaries of tectonic plates.
Question 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.
Answer:
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’.
Question 4.
State the precautions, that one should take for protection during an earthquake if one is (a) inside the house (b) Outdoors.
Answer:
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.
Question 5.
State the main precautions that can be taken to minimize the effect of an earthquake.
Answer:
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 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.
Question 1.
State the values displayed by Aakash.
Answer:
Care and concern for others
Question 2.
Name the quantity that is measured on the Richter Scale.
Answer:
Magnitude of earthquake
Question 3.
By what factor does the quantity go up when its magnitude on the Richter Scale increases by one?
Answer:
By a factor of 10
Something To Do
Question 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.
Answer:
Do it yourself
Question 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.
Answer:
Do it yourself
Question 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).
Answer:
Do it yourself
Question 4.
Fill the crossword with suitable words on the basis of the clues given below:
| Across → | Down ↓ |
| 1. Sudden shaking of earth. | 1. The point, on the earth’s surface, directly above the focus. |
| 2. Weak areas on the earth where the earthquake is more likely to occur. | 2. A scale used to rate the strength of an earthquake. |
| 3. Used to record seismic waves. | 3. Veiy large ocean waves. |
| 4. The place inside the earth’s crust from where the earthquake originates. | 4. Small quakes that may happen before the main quake. |
Answer:
| Across → | Down ↓ |
| 1: earthquake | 1: epicenter |
| 2: seismic zone | 2: richter scale |
| 3: seismograph | 3: tsunami |
| 4: focus | 4: foreshocks |
DAV Class 8 Science Chapter 18 Solutions – Earthquakes Important Questions and Answers
I. Fill in the blanks:
Question 1.
________ zones are highly susceptible to earthquakes.
Answer:
Seismic
Question 2.
The earth’s crust is divided into many ________ plates.
Answer:
tectonic
Question 3.
Focus of an earthquake is ________ the surface of the earth.
Answer:
below
Question 4.
________ of an earthquake is near the surface of the earth.
Answer:
Epicenter
Question 5.
A wooden house is ________ than a concrete house in case of earthquake.
Answer:
safer
II. Write ‘T’ for true and ‘F’ for false:
1. The focus of an earthquake is always below the ocean surface.
Answer:
False
2. The areas near the Himalayas are highly prone to earthquakes.
Answer:
True
3. People do not die of earthquakes but because of buildings which get damaged during it.
Answer:
True
4. Tsunami always comes before an earthquake.
Answer:
False
5. A large table is a safe place to hide under during an earthquake.
Answer:
True
III. Answer the following questions:
Question 1.
What can be the various effects of earthquake?
Answer:
Different effects of an earthquake are:
- Earthquake causes damages to the buildings, bridges, dams etc.
- Earthquakes can cause great loss of life.
- Earthquakes can also cause floods and landslides.
- An earthquake happening beneath the ocean floor can lead to a tsunami.
Question 2.
What is a tsunami?
Answer:
A series of huge seawaves consisting of high long walls of water which travel at a very rapid rate (about 960 km/hr) is called tsunami.
Question 3.
Write a brief note on seismometer.
Answer:
A device which is used for measuring the intensity of an earthquake is called seismometer. It consists of an oscillating device to which a pen is attached. The pen marks a graph like pattern on a paper. The graph is then interpreted by scientists to arrive at the conclusion.
Question 4.
Which type of precautions should be taken by a person if he is inside a room in case of an earthquake?
Answer:
Precautions for a person present inside a building are:
- Take shelter under a table and stay there till the shaking stops.
- Stay away from tall and heavy objects that may fall on you.
- 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.
Question 5.
Enlist the safety precautions after an earthquake.
Answer:
Safety Precautions after an Earthquake are:
- Stay calm for a while expect aftershocks. These shocks can cause additional damage.
- Beware of possible tsunami, if you live in coastal area.
- Carefully inspect utilities/supplies.
- Use telephones only in emergency.
- Stay away from damaged areas.
- Help the injured ones.
IV. Projects:
Question 1.
Make a list of five major earthquakes which happened in India in the recent past.
Answer:
Do it yourself
Question 2.
Make a list of five major earthquakes which happened outside India in the recent past.
Answer:
Do it yourself