DAV Class 8 Science Chapter 18 Notes – Earthquakes

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).

DAV Class 8 Science Chapter 18 Notes - Earthquakes

→ 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.

DAV Class 8 Science Chapter 18 Notes - Earthquakes

→ 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