Earthquake

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  • Minor earth tremors by wave of vibration within the earth crust.
  • Major earthquake by movement along faults.
  • Produce gigantic tidal wave called tsunami.
  • Major Earthquake: Great Lisbon Earthquake (1755) & Tokyo & Yokohama (1923), San Francisco (1906), Kansu in china (1920)
  • Regions of greatest seismicity are Circum-Pacific areas, with the epicentres and the most frequent occurrences along the ‘Pacific Ring of Fire’.
  • 70 % of earthquakes occur in the Circum-Pacific belt. Another 20% of earth quakes take place in the Mediterranean-Himalayan belt.
Earthquake waves
  • Suddern release of energy (Tremos/vibtations). The energy travel in the form of waves (Sesmic waves).
  • Focus – Point where earthquake first orginated/develop (Hypocenter)
  • Epicenter – Point on the surface of earth, where earthquake is first felt.
P    Waves
S waves
L Waves/ R Waves
  • Longitudinal   in nature
  • Faster
  • Travel   in all three Medium (Solid, Liquid, Gases)
  • Similar   to Property of sound waves
  • Longitudinal waves: Waves propagation parallel to Particle   vibration
  • Transvers   in nature
  • Relatively   slower than P waves.
  • Travel   only in solid Medium
  • Similar   to property/character of light waves.
  • Transvers waves: Waves propagation perpendicular to Particle   vibration.
  • Short   duration long waves.
  • Love   Waves.
  • Rayleigh   Waves.
  • Most   destructive in nature.
Reason for shadow zone
  • S waves – 105° - 105° - Because it asssed only solid.
  • P Waves – 105 - 145° - It passed all layers, but different density of layer reflect the wave pass.
Types of Earthquakes
  • Tectonic earthquakes - Sliding of rocks along a fault plane.
  • Volcanic earthquake - Special class of tectonic earthquake.
  • collapse earthquakes - Areas of intense mining activity.
  • explosion earthquakes - Explosion of chemical or nuclear devices.
  • Reservoir induced earthquakes. – Area of large reservoirs.
Measuring Earthquakes
  • Magnitude scale - Energy released – Richter scale (Range: 0-10).
  • Intensity scale – Damage caused – Mercalli (Range: 1-12).

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