Earthquakes - Geography - UPSC Notes

  • An earthquake refers to the shaking of the Earth's surface caused by the sudden release of energy in the Earth's crust.
  • The primary cause of earthquakes is the movement and interaction of tectonic plates. When stress builds up along plate boundaries, it is released in the form of seismic waves, leading to an earthquake.
  • The spot in the crust where these vibrations start, known as focus.
  • The place on the surface above the focus is known as the epicentre. 
  • The vibrations move outward from the epicentre in the form of waves. There are three types of earthquake waves: 1. P waves or longitudinal waves, 2. S waves or transverse waves and 3. L waves or surface waves.
  • The maximum damage happens usually closest to the epicentre. The intensity of the earthquake decreases from the centre.
  • Other causes include volcanic activity, human-induced activities such as mining or reservoir-induced seismicity.

Types of Earthquakes:

  • Tectonic Earthquakes: These occur due to the movement of tectonic plates along faults. They are the most common type of earthquakes.
  • Volcanic Earthquakes: These occur in volcanic regions and are associated with volcanic activity.
  • Induced Earthquakes: These are caused by human activities, such as mining, reservoir filling, or hydraulic fracturing (fracking).

Measurement and Magnitude:

  • The magnitude of an earthquake is a measure of the energy released during the seismic event. It is typically measured using the Richter scale or the moment magnitude scale (Mw).
  • The Richter scale measures the amplitude of seismic waves, while the moment magnitude scale considers the total energy released.
  • Each unit increase on the Richter scale represents a tenfold increase in the amplitude of ground motion and approximately 31.6 times more energy release. For example, an earthquake with a magnitude of 6.0 is ten times stronger than a magnitude 5.0 earthquake.
  • An earthquake of 2.0 or less can be classified as normal tremor. An earthquake of 5.0 and above can cause damage. An earthquake of 6.0 and above is classified as a strong earthquake and an earthquake of 7.0 and above is classified as a major earthquake.

Effects of Earthquakes:

  • Ground Shaking: The primary effect of an earthquake is the shaking of the ground, which can cause buildings, bridges, and infrastructure to collapse.
  • Surface Rupture: In some cases, the movement of faults during an earthquake can cause the ground to rupture, leading to visible cracks or displacement.
  • Aftershocks: Aftershocks are smaller earthquakes that occur after the main earthquake. They can continue for hours, days, or even months after the initial event.
  • Tsunamis: Underwater earthquakes or those near coastal regions can trigger tsunamis, which are large ocean waves capable of causing widespread devastation.

Earthquake Preparedness and Mitigation:

  • Seismic Zoning: Governments use seismic zoning to identify areas prone to earthquakes and enforce building codes accordingly.
  • Retrofitting: Strengthening existing structures to withstand seismic forces can significantly reduce the damage caused by earthquakes.
  • Early Warning Systems: Implementing early warning systems can provide valuable seconds to minutes of advance notice, allowing people to seek shelter and take necessary precautions.
  • Public Awareness and Education: Educating communities about earthquake preparedness, response strategies, and evacuation procedures is crucial in minimizing casualties.

Notable Earthquakes in India:

  • 2001 Gujarat earthquake: Magnitude 7.7 earthquake in Gujarat, causing extensive damage and loss of life.
  • 2004 Indian Ocean earthquake and tsunami: Magnitude 9.1 earthquake off the coast of Sumatra, triggering a devastating tsunami that affected multiple countries, including India.

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