These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 18 Notes – Earthquakes act as excellent revision resources, particularly in preparation for board exams.
Earthquakes Class 8 DAV Notes
→ Earthquake: A sudden tremor or movement of earth’s crust which lasts for a very short time is called earthquake.
→ Effects of an Earthquake:
- Earthquake causes damages to the buildings, bridges, dams.
- 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.
→ Tsunami: A series of huge seawaves, consisting of high long walls of water which travel at a very rapid rate (about 960 km/hr).
→ Cause of Earthquake:
The outermost surface of the earth is broken into a number of plates called lithospheric plates or tectonic plates. The tectonic plates keep on moving and a plate can slide against another plate or can climb upon another plate. The relative movement of tectonic plates results in shockwaves which causes earthquakes.
→ Focus: The point from which the earthquake originates is called the focus of the earthquake. Epicenter: The point at the surface of earth directly above the focus is called epicenter.
→ Measuring an earthquake: The intensity of an earthquake is measured on Richter scale. This scale was named after Dr. Charles F. Richter. The Richter scale is a logarithmic scale. An increase of two in the magnitude means 100 times more destructive energy.
→ Protection against Earthquakes:
- All the buildings in seismic zones need to be designed in a way that they can withstand major tremors.
- All buildings (specially tall) should have proper arrangement for fire fighting.
- All exit routes in a building must be clearly marked to facilitate in time evacuation of people. >- An emergency communication plan should be made available.
- Disaster management supplies should be available.
→ Safety Precautions During Earthquake:
1. For a person present inside a building:
- 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.
2. For a person caught outside in the open:
- Find a clear spot, away from buildings, trees, bridges and overhead power lines. Drop to the ground.
- Do not come out, if in a moving vehicle. Drive slowly to a clear spot and stay inside. Come out only when the tremors stop.
→ Safety Precautions After an Earthquake:
- Stay calm for a while expect aftershocks. These shocks can cause additional damage.
- Beware of poss.bie 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.
→ Tectonic Plates : The plates in which the earth’s crust is divided.
→ EpIcenter : The point on the surface directly above the focus of the earthquake.
→ Seismograph : A device which is used for measuring the intensity of an earthquake.
→ Seismology : The branch of science in which we study about earthquakes.
→ Seismometer: A device which is used for measuring the intensity of an earthquake. It consists of an oscillating device to which a pen is a.uaohed. The pen marks a graph like pattern on a paper. The graph is then interpreted by scientists to arrive at the conclusion.
|
Richter Scale |
|
| Magnitude | Effect of Quake |
| 2.5 | Generally not felt, but recorded on seismometer |
| 3.5 | Can be felt by many people |
| 4.5 | Some local damage (cracks in the buildings and dams may occur) |
| 6.0 | A destructive quake |
| 7.0 | A major destructive quake |
| 8.0 and above | A great quake, capable of destroying entire population |