Question

In which of the following Zones the earthquake waves are not reported
1. Protected Zone
2. Shadow Zone
3. Intense Zone
4. Low Intensity Zone

Answer 1

Correct Answer - Option 2 : Shadow Zone

The correct answer is Shadow Zone.

• The shadow zone is the area of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves.
• The shadow zone results from S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core. 

• An earthquake is a vibration of the surface of the earth that is caused due to the elasticity or the isostatic adjustment of the rocks under the surface of the earth that creates seismic waves.
• There are three types of seismic waves.
  • Primary or Longitudinal waves are also known as P-Waves: These are longitudinal waves analogous to the sound waves.
  • Secondary or Transverse Waves are also known as S-waves: These are transversal waves analogous to the light waves.
  • Surface or Long-period Waves are also known as L-Waves: They originate when ‘P’ wave hits the surface.
• The Bureau of Indian Standards grouped the country into four seismic zones namely Zone-II, Zone-III, Zone-IV, and Zone-V.
• Zone-V is the most seismic wave active region and Zone-II is the least.
  • Zone-II is known as the Low-intensity Zone. The intensity of the MM scale is less than or equal to 6.
  • Zone-III is known as the Moderate-intensity Zone. The intensity of the MM scale is equal to 7
  • Zone-IV is known as the Severe-intensity Zone. The intensity of the MM scale is equal to 8.
  • Zone-V is known as the Very Severe-intensity Zone. The intensity of the MM scale is equal to 9 and above.

 

• The instrument is used to detect and record earthquakes - Seismograph.
• The instrument is used to measure the magnitude of earthquakes - Ritcher Scale, Modified Mercalli Scale.