DAV Class 8 Science Solution Chapter 18 Earthquakes
DAV School Books Class 8 Science Solution Chapter 18 Earthquakes all Question Answer. DAV Class 8 18th Chapter Earthquakes full Chapter explanation by expert teacher.
DAV School Books Class 8 Science Solution Chapter 18 Earthquakes
A.) Fill in the blanks.
1.) ___________ 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 ___________.
3.) Earthquake is caused by a disturbance deep inside the ___________ of earth.
4.) The waves, associated with the tremors caused by earthquakes, are known as ___________ waves.
5.) Geologists, call the point of origin of earthquakes, as its ___________.
6.) Destructive energy of an earthquake is measured on the ___________ scale.
Answer: (1) Foreshock (2) Tsunami (3) crust (4) seismic (5) focus (6) Richter.
B.) State True or False for the following statements.
1.) It is now possible to give exact predictions about the earthquakes.
2.) Earthquakes, beneath the ocean floor, can generate huge tidal waves.
3.) When the plates of the earth slide past each other, the energy released gives rise to waves known as seismic waves.
4.) Richter Scale is a simple linear scale.
5.) An earthquake of magnitude 2.5 on the Richter Scale, cannot be recorded on a seismometer.
6.) In highly seismic areas, it is better to have houses made from mud or timber, than those made by using heavy construction materials.
Answer: (1) False, No it is not possible to exactly predict earthquakes (2) True (3) True (4) False, It is more complicated than linear scale (5) False , yes it can be recorded (6) True.
C.) Tick the correct option.
1.) The minor quake, that might occur before the main earthquake, is known as a-
Answer: foreshock
2.) A natural phenomenon, whose triggering is not associated with an earthquake, is-
Answer: flood
3.) Earthquakes occur when there is a sudden release of stored up energy in earth’s-
Answer: crust
4.) The various layers of earth are marked as A, B, C and D as shown in the given figure.
The correct labelling, of these layers A, B, C and D of earth, is-
Answer: A. crust, B. mantle, C. outer core, D. inner core
5.) The epicenter of an earthquake is-
Answer: on the surface of earth
6.) The magnitudes of two earthquakes, A and B, on the Richter Scale, were 7 and 5, respectively. The strength of-
Answer: earthquake A is 100 times that of earthquake B.
D.) Answer the following questions in brief.
1.) What is an earthquake?
Answer: A natural occurrence called an earthquake happens when the tectonic plates of the Earth shift and release energy. Seismic waves, which are created when this energy is released, travel through to the Earth’s crust but also cause the ground to tremble, shift, and move. The epicentre is the location on the Earth’s crust directly just above focus, while the focus is the location within the Earth’s crust in which the shock waves begin. Tectonic plates, volcanic eruptions, and human activities like underground mining or digging are few of the causes of earthquakes.
2.) State any three of the ‘damaging effects’ of an earthquake.
Answer: The three damaging effects of an earthquake are as follows:
- The ground shaking is the most evident and immediate result of an earthquake. Buildings, highways, railroads, as well as other structures may sustain damage as a result. Landslides, falling rocks, as well as other sorts of earth movement can also result from the shaking.
- Tsunamis, which are enormous waves that can significantly damage structures, infrastructure, and coastal communities, can be produced by earthquakes that take place in coastal regions. Flooding and other sorts of destruction can also be brought on by tsunamis.
- Other hazards like rockfalls, landslides, dam failures, and even volcanic eruptions can be brought on by earthquakes. These incidental dangers may result in additional harm and fatalities.
3.) Explain the phenomenon of production of shock waves.
Answer: Natural events like volcanic eruptions and earthquakes can also produce shock waves. Seismic waves are produced when the continental plate shift and release energy. Some of this energy is discharged as a shock wave when the seismic waves reach the surface of the Earth. Similar to how a shock wave is produced when a volcano erupts, a pressure wave is produced when an explosion travels through the atmosphere.
4.) In the context of an earthquake, which of the two points: the focus or the epicenter, is deep under the ground?
Answer: The focus (also known as the hypocenter) of an earthquake is located deep underground, while the epicentre is located above ground.
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: The Richter scale is used to determine an earthquake’s intensity. Since the Richter scale is a measurement unit, a rise in magnitude corresponds to a tenfold increase in seismic wave amplitude.
(a) A minor earthquake would probably have a Richter scale value of 3 or less.
(b) An earthquake with a high level of devastation would probably have a Richter scale intensity of 7 or higher.
6.) An earthquake measures 3 on Richter Scale.
(a) Would it be recorded on the seismometer?
Answer: Yes, it will be recorded on the seismometer.
(b) Is it likely to cause much damage?
Answer: No, it is a very mild earthquake.hence any damage is unlikely to be caused.
E.) Answer the following questions.
1.) Explain, in brief, the cause of an earthquake.
Answer: Tectonic plate motion in the Earth’s crust is what causes earthquakes. The crust of the Earth is composed of a series of huge plates and a number of smaller plates, all of which are mobile. These plates are changing gradually, receding, or sliding past one another. The strain and pressure created by the action of two plates grinding against one another can accumulate over time. The accumulated energy will eventually be released as seismic waves when the plates finally shift, giving us the sensation of an earthquake.
2.) Where are the earthquakes more likely to occur?
Answer: Where the tectonic plates of the Earth’s crust meet or part, this is where earthquakes are most probable to occur. The most of earthquakes happen near the junctions of the crustal plates of the Earth. As with intraplate earthquakes, which are more uncommon than plate boundary earthquakes but can still have a big impact when they do happen, earthquakes can also happen inside the 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.
Answer: All homes should be built in accordance with the most recent seismic zone building norms and standards, according to Mr. Sarthak’s business. This entails the use of seismic-resistant components and design strategies, such as bases, walls, including roofs. To keep the homes earthquake-resistant, the business should perform routine inspections and perform any required maintenance.
4.) State the precautions, that one should take for protection during an earthquake if one is (a) inside the house (b) outdoors.
Answer: (a) Precautions to take for protection during an earthquake if one is inside the house:
- Until the shaking stops, seek refuge under a piece of substantial furniture, like a desk or a table, and hang on to it.
- Avoid using heavy furniture that could fall over and injure you, such as bookcases and refrigerators.
- If in bed, stay on the bed and cover the head with pillows.
- If at all possible, stay inside and stay away from glass, mirrors, and other potentially dangerous objects.
(b) Precautions to take for protection during an earthquake if one is outdoors:
- Locate a space that is open and distant from structures, electricity wires, and other potential dangers.
- If a person is driving, they should stop the car and pull over in a secure location.
5.) State the main precautions that can be taken to minimise the effect of an earthquake.
Answer: The main precautions are as follows:
- Staying after the initial earthquake.
- Doing an inventory check of supplies and kits.
- Telephones should be used only in emergencies.
- Staying informed regarding any tsunami warnings for coastal areas.
- Staying away from danger zones.
- Helping others in need.