Earthquake & Seismic Zones
Disaster Management · भूकंप और भूकंपीय क्षेत्र
📋Quick Overview
India lies in a seismically active zone because the Indian tectonic plate is actively colliding with the Eurasian plate, creating the Himalayas and causing frequent earthquakes. The Bureau of Indian Standards (BIS) divides India into four seismic zones (II to V) based on earthquake intensity. About 54% of India's land area is prone to earthquakes, with Zone V being the most vulnerable.
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India has 4 seismic zones (II, III, IV, V) — Zone V is the highest risk. The entire northeastern India, J&K, Himachal Pradesh, Uttarakhand, parts of Gujarat (Kutch), and Andaman & Nicobar fall under Zone V.
📖India's Four Seismic Zones (BIS IS-1893)
| Zone | Risk Level | Intensity (MSK Scale) | Key States/Regions |
|---|---|---|---|
| Zone II | Low Risk | VI or less | Most of South India, Rajasthan interior, MP, Gujarat coast |
| Zone III | Moderate Risk | VII | Kerala, Goa, Lakshadweep, parts of Maharashtra, MP, UP, Punjab, Haryana |
| Zone IV | High Risk | VIII | Delhi, North Bihar, Uttarakhand plains, J&K hills, HP hills, parts of Maharashtra (Koyna) |
| Zone V | Very High Risk (Most Prone) | IX or more | Entire NE India, J&K (Kashmir valley), HP, Uttarakhand, Kutch (Gujarat), Andaman & Nicobar |
📖Seismic Waves & Measurement
| Wave Type | Full Name | Speed | Medium | Effect |
|---|---|---|---|---|
| P-waves | Primary/Compressional waves | Fastest (6-8 km/s in crust) | Solids + liquids + gases | Push-pull motion; least damage |
| S-waves | Secondary/Shear waves | Slower than P (3-4 km/s) | Only solids | Side-to-side motion; moderate damage |
| L-waves (Love) | Surface/Love waves | Slowest | Earth's surface | Horizontal shaking; maximum damage |
| R-waves (Rayleigh) | Surface/Rayleigh waves | Slowest | Earth's surface | Rolling motion; creates most destruction |
- •Hypocenter (Focus): Point inside the Earth where earthquake energy is released; Epicenter: Point on Earth's surface directly above the focus — experiences maximum damage
- •Richter Scale: Developed by Charles Richter (1935); measures magnitude (0-10); logarithmic — each step = 10× more energy; magnitude 7+ = major earthquake
- •Modified Mercalli Scale (MMI): Measures intensity (I-XII) based on effects observed; I = not felt; XII = total damage; subjective scale unlike Richter
📝Major Earthquake-Prone Fault Lines in India
- •Himalayan Frontal Thrust (HFT): Main thrust fault along Himalayas — causes most earthquakes in northern India
- •Andaman-Nicobar arc: Subduction zone where Indian plate dives under Burma plate — high seismicity including 2004 tsunami event
- •Kutch Fault Zone (Gujarat): Intra-plate seismicity; caused 2001 Bhuj earthquake (7.6 magnitude)
- •Shillong Plateau: High risk zone; 1897 Assam earthquake (8.7 magnitude) was one of the largest recorded in India