Earthquakes & Landslides: Tectonic and Slope Hazards
UPSC Mains PYQs
- Landslides & Himalayan Vulnerability (2016): "Landslides are a major hazard in the Himalayan region, which has been exacerbated by unscientific infrastructure development." Critically analyze the natural and anthropogenic causes of landslides in the Himalayas and compare them with the Western Ghats. Discuss the key recommendations of NDMA Guidelines for landslide risk management. (15 Marks, 250 Words)
📊 High-Yield Data & Statistical Fact Sheet
- Geological Risk Metrics:
- Seismic Share: 61% of India's landmass is vulnerable to moderate-to-severe earthquakes (Zones III, IV, and V).
- Zone V Extent: Covers Northeast India, J&K, Himachal Pradesh, Uttarakhand, Rann of Kutch, and parts of Bihar.
- Landslide Zone: 12.6% of national territory (~0.42 Million sq km) is classified as landslide-susceptible.
- Seismic Stations: NCS maintains a real-time tracking grid of 150+ stations across India.
Earthquake Vulnerability Share (%)
Loading chart...
Landslide Vulnerability Share (%)
Loading chart...
1. EARTHQUAKE RISK & SEISMIC MICROZONATION
- BIS Zonation Map: Bureau of Indian Standards divides India into four seismic zones: Zone II (Low), Zone III (Moderate), Zone IV (High), and Zone V (Very High). (Zone I is merged into Zone II).
- Seismic Microzonation: Subdividing a municipal territory into micro-zones based on local soil density and rock characteristics to identify soil liquefaction and amplification factors. Helps customize building bye-laws for high-density metropolitan areas.
- National Center for Seismology (NCS): The nodal body under the Ministry of Earth Sciences responsible for monitoring seismic activity and deploying early warning systems.
2. LANDSLIDE DYNAMICS: HIMALAYAS VS. WESTERN GHATS
Landslide hazards diverge significantly in geological origin and trigger mechanisms:
| Parameter | Himalayan Region | Western Ghats Region |
|---|---|---|
| Geological Age | Geologically young, active fold mountains. | Geologically ancient, stable block mountains. |
| Tectonic Activity | Highly active; frequent tectonic shocks. | Relatively stable; low tectonic activity. |
| Trigger Factors | Triggered by both intense rainfall and seismic shocks. | Triggered almost exclusively by extreme monsoonal rainfall. |
| Slope & Relief | High vertical relief, steep slopes, loose shale. | Escarpments with soil cover, debris flow along valleys. |
| Human Stressors | Road cuts (Char Dham widening), tunnel blasting, dams. | Tea/coffee plantations, resort construction, quarrying. |
3. NDMA GUIDELINES FOR GEOLOGICAL RISK MITIGATION
- Structural Interventions:
- Slope Stabilization: Construction of retaining walls, rock bolting, and soil nailing.
- Bio-Engineering: Sowing soil-binding species (e.g., Vetiver grass) to anchor loose slopes.
- Building Code Enforcement: Mandating earthquake-resistant construction for all public assets (schools, hospitals).
- Non-Structural Interventions:
- NLSM Program: Geological Survey of India's (GSI) National Landslide Susceptibility Mapping to restrict slope constructions.
- LEWS (Early Warning): Integrating real-time satellite rainfall sensors to predict landslide events 24–48 hours in advance.
QUICK REVISION BOX
- Earthquake Nodal Monitor: National Center for Seismology (NCS).
- Landslide Nodal Agency: Geological Survey of India (GSI).
- Standard Seismic Zoning Authority: Bureau of Indian Standards (BIS).
- Active Indian Seismic Zones: Zone II, III, IV, V (four zones).
- Micro-Soil Risk Analysis: Seismic Microzonation.
- National Landslide Mapping Database: NLSM (GSI-run).
- Himalayan Trigger Doublet: Rainfall & Seismicity.
Notes updated up to March 2026. Sources: GSI Bulletins, NCS Reports, NDMA Guidelines.