Earthquakes – UPSC Rapid Revision 

🔹 Basics

1. Definition – Sudden release of energy in Earth’s lithosphere causing seismic waves.

2. Focus/Hypocenter – Point inside Earth where quake originates.
   Epicenter – Point on surface above focus.

🔹 Causes

3. Tectonic (plate movement – majority).

4. Volcanic (magma movement).

5. Collapse (caves, mines).

6. Explosion (man-made, e.g., nuclear).

🔹 Measurement

7. Magnitude – Richter Scale / Moment Magnitude Scale (Mw).

8. Intensity – Mercalli Scale (I–XII, damage-based).

🔹 Distribution

9. Seismic Belts –

   • Circum-Pacific ("Ring of Fire").

   • Mid-Atlantic Ridge.

   • Himalayan belt (Alpine-Himalayan).

🔹 India’s Seismicity

10. Seismic Zones – Zone II (least) to Zone V (highest).

• Zone V: NE India, Kashmir, Himachal, Uttarakhand, Rann of Kutch, Andamans.

11. Major Past Quakes –

• 1897 Shillong (M 8.1)

• 1934 Bihar-Nepal (M 8.4)

• 2001 Bhuj (M 7.7)

• 2015 Nepal (M 7.8).

🔹 Impacts

12. Primary – Ground shaking, surface rupture, landslides.

13. Secondary – Tsunami, fires, liquefaction, dam failures.

🔹 Preparedness & Mitigation

14. Institutional Framework (India) –

• National Disaster Management Authority (NDMA).

• IMD (monitoring).

• NCS (National Center for Seismology).

15. Way Forward –

• Earthquake-resistant construction.

• Early-warning systems.

• Community drills + zoning laws.