Earthquakes, Landslides & Urban Disasters

Earthquakes

An earthquake is the shaking of the Earth's surface caused by a sudden release of energy in the lithosphere, producing seismic waves. India is highly vulnerable — approximately 59% of India's landmass is prone to moderate to severe earthquakes (Zones III-V).

Seismic Waves: P-Waves vs S-Waves

Shadow zone: S-waves cannot pass through Earth's liquid outer core, creating a shadow zone between 104-140 degrees from the epicentre. P-waves are refracted by the core, creating a shadow zone between 104-140 degrees as well (though they re-emerge beyond 140 degrees).

Measuring Earthquakes: Richter vs Mercalli Scale

Note: The Richter scale has been largely superseded by the Moment Magnitude Scale (Mw) for scientific use, which better measures large earthquakes. Media still commonly refers to "Richter scale" readings.

Seismic Zones of India (BIS Classification)

The Bureau of Indian Standards (BIS) classifies India into four seismic zones (II to V) under IS 1893. Zone I was merged with Zone II in the 2002 revision.

• ~11% of India falls in Zone V, ~18% in Zone IV, ~30% in Zone III, and the rest in Zone II.
• Over 60% of India's landmass faces moderate to high earthquake hazard.

2025 Update: BIS revised the Earthquake Design Code (IS 1893:2025) introducing a new Zone VI (Super-Critical Zone), placing the entire Himalayan belt from Jammu & Kashmir to Arunachal Pradesh under the highest risk category. India now has five seismic zones (II to VI).

Major Earthquakes Affecting India

Tsunamis

A tsunami is a series of ocean waves generated by large-scale disturbances — usually undersea earthquakes, but also submarine landslides and volcanic eruptions. The word comes from Japanese: "tsu" (harbour) + "nami" (wave).

Indian Ocean Tsunami (26 December 2004)

The deadliest tsunami in recorded history was triggered by a magnitude 9.1 undersea earthquake off the coast of Sumatra, Indonesia.

Indian Tsunami Early Warning System

Post-2004, India established a robust early warning network.

Landslides

A landslide is the movement of rock, debris, or earth down a slope under gravity. India is among the top five landslide-prone countries globally.

Causes of Landslides

Landslide-Vulnerable Zones in India

Recent Landslide Disasters

Wayanad Landslides (30 July 2024):

• Location: Mundakkai, Chooralmala, and Vellarimala villages in Meppadi panchayat, Wayanad district, Kerala
• Deaths: Over 250 confirmed deaths, 200+ missing; Kerala government later declared all missing persons dead (February 2025)
• Cause: Intense rainfall triggering massive debris flow (~6 million cubic metres)
• Victims: Predominantly tea and cardamom estate workers, struck while asleep in early hours
• Significance: One of India's deadliest landslide events in modern history

Joshimath Subsidence Crisis (January 2023 onward):

• Location: Joshimath town, Chamoli district, Uttarakhand
• Crisis: Land subsidence — parts of the town sank by over 30 cm between December 2022 and December 2024
• Cause: Town built on ancient landslide deposits (sand and stone, not bedrock); uncontrolled construction, poor drainage, internal erosion from water infiltration
• Impact: ~900 houses developed cracks; ~1,000 people evacuated; continuing slow subsidence
• Significance: Raised alarm about unplanned development in fragile Himalayan ecology

NDMA Guidelines on Landslides

• Landslide Hazard Zonation (LHZ) mapping on 1:50,000 and 1:25,000 scales
• Land-use regulations restricting construction in high-risk zones
• Bio-engineering measures — afforestation, grass planting on slopes
• Structural measures — retaining walls, check dams, proper drainage
• Early warning systems using rain gauges, inclinometers, and satellite monitoring

Urban Disasters

Rapid urbanisation, poor planning, and crumbling infrastructure make Indian cities increasingly vulnerable to a range of disasters.

Urban Flooding

Root causes of urban flooding: Encroachment on flood plains and wetlands, concretisation reducing percolation, inadequate storm-water drainage, unregulated construction, and climate change intensifying extreme rainfall events.

Fire and Building Collapse

Urban India faces frequent fire incidents in factories, high-rises, slums, and commercial establishments. Key issues include:

• Non-compliance with fire safety norms and National Building Code
• Narrow lanes impeding fire-tender access (especially in old city areas)
• Illegal constructions, poor structural audits
• Lack of fire NOC (No Objection Certificate) enforcement

Heatwaves in Cities

Urban Heat Island (UHI) effect makes cities 2-5 degrees Celsius hotter than surrounding rural areas. India recorded over 2,000 heatwave-related deaths in 2015 (Andhra Pradesh and Telangana worst hit). NDMA's Heat Action Plans (first introduced by Ahmedabad in 2013) are now implemented in many cities.

National Disaster Response Force (NDRF)

The NDRF is India's specialised disaster response force, constituted under Section 44 of the Disaster Management Act, 2005.

Parent Forces (Composition)

Note: The total above sums to 13 battalions from the originally listed forces. The remaining battalions were added through subsequent expansions approved by the Union Cabinet to strengthen coverage.

NDRF Deployment

• Present at 68 locations including 28 Regional Response Centres (RRCs) and 24 Tactical Pre-positioning Locations (TPLs)
• Pre-positioned before cyclones, floods, and other anticipated disasters
• Specialised in CBRN (Chemical, Biological, Radiological, Nuclear) emergencies
• Conducts community awareness programmes, mock drills, and school safety initiatives
• Aapda Mitra scheme trains community volunteers in disaster-prone districts

Community-Based Disaster Management (CBDM)

CBDM is a bottom-up approach that recognises local communities as the first responders in any disaster. NDMA released comprehensive guidelines on Community Based Disaster Risk Reduction (CBDRR) in 2014, updated in October 2024.

Core Principles

• People-centred: Communities identify their own risks, vulnerabilities, and capacities
• Participatory: Involvement of all sections — women, elderly, disabled, marginalised groups
• Decentralised: PRIs (Panchayati Raj Institutions) and ULBs (Urban Local Bodies) as institutional anchors
• Knowledge-based: Combines scientific knowledge with indigenous/traditional knowledge

Institutional Mechanism

Key CBDM Components

• Village/Ward Disaster Management Plans: Community-prepared plans identifying hazards, safe areas, evacuation routes, resource inventory, and vulnerable populations
• Task Forces: Trained teams for search and rescue, first aid, early warning dissemination, shelter management
• Mock Drills: Regular community-level drills to test preparedness — NDMA conducts annual national mock drills
• Indigenous Knowledge: Traditional practices like flood-resistant housing in Assam (chang ghar / houses on stilts), cyclone-resistant construction in Odisha
• Aapda Mitra Scheme: Government programme to train 1,00,000 community volunteers across 350 disaster-prone districts in flood, landslide, cyclone, and earthquake response

Man-Made Disasters

Man-made (anthropogenic) disasters result from human action, negligence, or technological failure.

Classification

Bhopal Gas Tragedy (2-3 December 1984)

The world's worst industrial disaster — a benchmark case for industrial safety regulation globally.

Key Regulatory Responses to Man-Made Disasters

UPSC Relevance

Prelims Focus Areas

• Seismic zones of India — BIS classification (Zone II to V, new Zone VI from 2025), zone factors, MSK intensity
• P-waves vs S-waves — properties, shadow zones
• Richter vs Mercalli vs Moment Magnitude scales
• Indian Ocean Tsunami 2004 — date, magnitude, death toll
• INCOIS and Indian Tsunami Early Warning Centre — location (Hyderabad), DART buoys
• NDRF — number of battalions (16), parent forces, Section 44 of DM Act 2005
• Bhopal Gas Tragedy — year (1984), gas (MIC), company (Union Carbide)
• Landslide-vulnerable zones — Himalayas, Western Ghats, NE India
• Environment Protection Act 1986 — connection to Bhopal tragedy

Mains Focus Areas

• Earthquake preparedness in India — gaps in building codes, retrofitting challenges
• Urban flooding — why Indian cities flood repeatedly; systemic solutions
• Joshimath crisis — development vs ecological fragility in the Himalayas
• CBDM — why a bottom-up approach is essential; role of PRIs and community volunteers
• Man-made disasters — regulatory gaps, compliance deficit, need for stricter enforcement
• Technology in disaster management — EWS, satellite monitoring, AI for disaster prediction
• Sendai Framework alignment — how India is implementing DRR commitments
• NDRF capacity and reach — is 16 battalions enough for a country of India's size?
• Climate change amplifying disaster frequency and intensity — adaptation strategies

Vocabulary

Seismic

• Pronunciation: /ˈsaɪz.mɪk/
• Definition: Relating to or caused by earthquakes or other vibrations of the Earth's crust, or more broadly, having a significant or far-reaching effect.
• Origin: From Ancient Greek seismós (σεισμός, "shaking, earthquake"), from seíein ("to shake") + the suffix -ic; first used in English in the 1850s.

Liquefaction

• Pronunciation: /ˌlɪk.wɪˈfæk.ʃən/
• Definition: A phenomenon in which saturated, loosely packed soil or sediment loses its strength and stiffness during earthquake shaking, behaving temporarily as a liquid rather than a solid, causing buildings to sink and infrastructure to collapse.
• Origin: From French liquéfaction, from Late Latin liquefactiōnem, from Latin liquefacere ("to make liquid"), from liquēre ("to be fluid") + facere ("to make"); used in English from the 17th century, with the geological sense developing in the 20th century.

Epicentre

• Pronunciation: /ˈɛp.ɪˌsɛn.tər/
• Definition: The point on the Earth's surface directly above the focus (hypocentre) of an earthquake, where seismic shaking is usually most intense and damage most severe.
• Origin: From Modern Latin epicentrum (1879), from Greek epí (ἐπί, "upon, over") + kéntron (κέντρον, "centre"); first used in seismology in 1885.

Key Terms

Richter Scale

• Pronunciation: /ˈɹɪx.tər skeɪl/
• Definition: A logarithmic scale devised in 1935 by American seismologists Charles F. Richter and Beno Gutenberg at the California Institute of Technology to measure earthquake magnitude based on the logarithm of the maximum trace amplitude of seismic waves recorded by a seismograph at a distance of 100 km. Each whole-number increase represents a tenfold increase in wave amplitude and approximately 31.6 times more energy released. The scale was replaced in the 1970s by the Moment Magnitude Scale (Mw), developed by Hiroo Kanamori and Thomas C. Hanks, which better measures large earthquakes (above magnitude 7); for adequately measured earthquakes, numerical values are approximately the same on both scales.
• Context: Named after Charles Francis Richter (1900-1985); originally called simply a "magnitude" scale at the suggestion of Harry Wood. The scale was first presented in Richter's 1935 paper. While media still commonly refers to "Richter scale" readings, scientists now use the Moment Magnitude Scale (Mw) as the global standard because the original Richter scale saturates (cannot distinguish) earthquakes above about magnitude 6.5. The 2001 Bhuj earthquake measured 7.7 Mw, and the 2004 Indian Ocean earthquake measured 9.1 Mw.
• UPSC Relevance: GS1 Physical Geography and GS3 Disaster Management. Prelims tests the logarithmic nature (10x amplitude, ~31.6x energy per unit), the distinction between Richter and Moment Magnitude (Mw) scales, and the difference between magnitude (energy released, single value per earthquake) and intensity (damage felt, varies by location, measured on Modified Mercalli Intensity scale, I to XII). Mains connects to earthquake preparedness, building codes (BIS IS 1893), and why accurate magnitude measurement matters for early warning, emergency response planning, and seismic zone classification.

Seismic Zones of India

• Pronunciation: /ˈsaɪz.mɪk zəʊnz əv ˈɪn.di.ə/
• Definition: The classification of India's landmass into earthquake risk zones by the Bureau of Indian Standards (BIS) under IS 1893, based on seismic intensity, historical earthquake data, and probabilistic seismic hazard assessment. Originally comprising four zones (II to V), updated in 2025 (IS 1893:2025) to include a new Zone VI (Super-Critical Zone) covering the entire Himalayan belt from J&K to Arunachal Pradesh, the Andaman & Nicobar Islands, and parts of North Bihar and Gujarat, making five zones in total. Zone factors range from 0.10 (Zone II, low risk) to 0.36 (Zone V) with Zone VI representing the highest hazard.
• Context: The BIS seismic zonation framework was first established in 1962; the four-zone system (merging Zone I into Zone II) was adopted in the 2002 revision. The 2025 revision introduced Zone VI based on modern Probabilistic Seismic Hazard Assessment (PSHA) and stress accumulation data, recognising that the earlier maps underestimated hazard from long-locked sections of the Himalayan megathrust fault that have not produced a major rupture for nearly two centuries but continue to accumulate stress. Approximately 61% of India's landmass now lies in moderate to high hazard zones (III to VI). Key zone allocations: Zone VI (Himalayan belt, NE India, A&N), Zone IV (Delhi-NCR, parts of J&K, HP, Bihar), Zone III (Mumbai, Kolkata, Chennai), Zone II (most of peninsular India).
• UPSC Relevance: GS3 Disaster Management. Prelims tests which zones cover which major cities -- Delhi (Zone IV, not V), Guwahati/Srinagar (Zone V/VI), Mumbai/Chennai (Zone III) -- and the 2025 introduction of Zone VI (Super-Critical). Mains asks about earthquake preparedness in India, poor enforcement of building codes in seismic zones (especially urban areas), why ~61% of India is vulnerable, and the policy implications of Zone VI for construction standards in the Himalayan belt. The IS 1893:2025 revision is a significant current affairs development frequently tested alongside the Joshimath subsidence crisis.