Earthquakes in India – Risk and impact

Earthquake Zones of India

Seismic Zoning of India

• According to the latest seismic zone map by the National Disaster Management Authority (NDMA):
  • Nearly 59% of India’s land area is prone to moderate to severe earthquakes.
• India is divided into five seismic zones based on earthquake intensity.

👉 Zone-wise Distribution:

• Zone 5 (Highest risk):
  • Covers Northeast India, Jammu & Kashmir, Uttarakhand, and parts of Himachal Pradesh.
• Zone 4 (High risk):
  • Includes Delhi and surrounding areas.
• Zone 3 (Moderate risk):
  • Covers much of Central India.
• Zone 2 (Low risk):
  • Most of Southern India.
• Zone 1: Earlier classification, but in the latest maps, Zone 1 is largely merged with Zone 2.

Earthquakes in Delhi–NCR Region

• Delhi falls in Seismic Zone 4, but its location makes it particularly vulnerable.
• It is close to multiple active tectonic faults, such as:
  • Mahendragarh–Dehradun Fault (MDF)
  • Sohna Fault (SF)
  • Mathura Fault (MF)

👉 Seismic Gap – A Silent Danger

• In the Northwest Himalayas, there is a 500 km long Central Himalayan Seismic Gap.
• This area hasn’t experienced a very large earthquake in the past 200–500 years.
• This suggests a significant accumulation of strain/energy, which could release in a major quake.

📌 Definition:

• A Seismic Gap = A fault segment that has not experienced earthquakes for a long time, despite being in an active seismic region.
• It indicates stored strain energy and hence is a potential future epicentre of a big quake.

Earthquakes in the North-East India

• Northeast India is one of the most seismically fragile regions of the world.
• Why so?
  • Because of the complex tectonic setting:
    • East–West trending Himalayas meet the North–South trending Arakan Yoma belt.
    • Several active faults crisscross the region, e.g.:
      • Po Chu Fault
      • Kopili Fault
      • Jiali Fault

The Kopili Fault Zone

• A major fault zone in Northeast India.
• Characteristics:
  • Length: ~300 km
  • Width: ~50 km
  • Extends from Western Manipur to the tri-junction of Bhutan, Arunachal Pradesh, and Assam.
  • It is a tectonic depression, filled with alluvium from the Kopili River (a tributary of Brahmaputra).

👉 Why important?

• The Kopili Fault lies close to the Himalayan Frontal Thrust (Main Frontal Thrust – MFT).
• The Himalayan Thrust Fault marks the boundary between the Indian Plate and Eurasian Plate.
• This is a convergent boundary → Indian Plate is subducting beneath the Eurasian Plate.
• Hence, it falls under Seismic Hazard Zone V (highest risk).

Effects of Earthquakes,

1. Shaking and Ground Rupture

• The primary effect of an earthquake is ground shaking.
• This causes severe damage to rigid structures like:
  • Buildings
  • Dams
  • Bridges
  • Nuclear power stations
• Ground rupture = when the fault line literally cracks the ground surface.
• For large engineering structures (e.g., pipelines, metro lines), this is extremely dangerous.

2. Landslides and Avalanches

• Earthquakes destabilize slopes, causing landslides and snow avalanches.
• Particularly common in mountain regions like the Himalayas.
• Earthquakes act together with other hazards—storms, volcanic eruptions, or coastal erosion—to trigger mass movements.

3. Fires

• Earthquakes can rupture electrical lines, gas pipes, and fuel storage tanks.
• This often leads to uncontrollable fires in urban areas.
• Example: 1906 San Francisco Earthquake → more deaths occurred due to fire than due to shaking itself.

4. Soil Liquefaction

• Happens in water-saturated soils.
• During intense shaking, soil particles lose contact with each other → soil behaves like a liquid instead of a solid.
• Effects:
  • Buildings and bridges may tilt, sink, or collapse.
  • Ground stability is lost, making construction in such areas very risky.
• Example: Observed during the 1964 Niigata Earthquake (Japan).

5. Tsunami

• Caused by Megathrust Earthquakes at subduction zones.
• When the sea floor abruptly moves, it displaces huge volumes of water.
• Generates long-wavelength, long-period sea waves → called tsunami.
• Tsunami can travel thousands of kilometers with devastating impact.
• Example: 2004 Indian Ocean Earthquake and Tsunami.

6. Floods

• Secondary effect of earthquakes.
• Can occur in two ways:
  1. Damage to dams → sudden water release.
  2. Landslides block rivers → form temporary lakes → when these collapse, catastrophic floods occur.
• Example: In mountainous areas like the Himalayas, such flood hazards are common after seismic activity.

💡 UPSC Answer-Writing Tip:
Whenever asked about the “impact of earthquakes,” always divide into primary effects (shaking, rupture) and secondary effects (landslides, fires, liquefaction, tsunami, floods). This shows structured thinking.