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Note: The Richter scale has been largely superseded by the Moment Magnitude Scale (Mw) for scientific use, which better measures large earthquakes.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
• Tibet earthquake: 7 January 2025; Mw 7.1 (USGS); Shigatse/Tingri; 126+ deaths; normal faulting
• Myanmar earthquake: 28 March 2025; Mw 7.7; Sagaing Fault (right-lateral strike-slip); Mandalay; 3,645+ deaths; supershear rupture

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

Cross-paper relevance

• GS3 — Disaster Management (primary) — Earthquakes, landslides, urban disasters: Wayanad landslides (400+ deaths, July 2024), Joshimath land subsidence, seismic zone mapping, NBC 2016
• GS3 — Environment — Climate dimension: climate change increasing landslide frequency, Himalayan instability due to glacier retreat, permafrost thaw
• GS2 — Governance/urban dimension: DM Act Amendment (UDMAs), urban planning failures, illegal construction, building regulation enforcement gaps
• Essay — Recurring theme: "Urban disasters: man-made as much as natural" (2022); "Himalayan fragility: development vs. conservation" (2021)

Recent Developments (2024–2026)

Wayanad Landslides — India's Deadliest Recent Disaster (July 2024)

The Wayanad landslides of 30 July 2024 — striking the Mundakkai and Chooralmala areas of Kerala's Wayanad district — killed over 400 people (death toll reached 408 confirmed, with many missing) and displaced 10,000+. The landslide was triggered by a geological cascade: intense rainfall (272 mm in 24 hours) on saturated slopes in a region with high coffee and tea plantation cover (replacing dense forests that provided slope stability).

A total of 1,531 rescuers were mobilised including NDRF, Indian Army (582 personnel), Air Force, Navy, and Kerala Police. The disaster exposed: lack of early warning for localised landslides (unlike cyclones, no community-level landslide warning system existed); gap between geological vulnerability mapping and land-use regulation; and the specific vulnerability of plantation workers (predominantly ST communities) who lived in the slide zone.

Kerala's Rebuild Wayanad project — a ₹900 crore (requested from Centre) rehabilitation programme — includes relocating 3,000 families from the highest-risk zones to new cluster settlements with community facilities.

UPSC angle: Prelims — Wayanad landslide: 30 July 2024; Mundakkai/Chooralmala; 400+ deaths; 1,531 rescuers. Mains (GS3) — landslide vulnerability and land-use change; plantation ecology and slope stability; early warning gap for localised slope failures.

Tibetan Plateau Earthquake — Mw 7.1 (7 January 2025)

A Mw 7.1 earthquake struck Tingri County, Shigatse prefecture, Tibet Autonomous Region, on 7 January 2025 at 09:05 CST (USGS; Al Jazeera, January 2025). The epicentre is approximately 235 km north-northwest of Kathmandu. The death toll was at least 126 (initial confirmed) rising to an estimated 400+ across subsequent reports; 338 were injured. Shaking was felt across Nepal, Bhutan, and northeast India; minor injuries reported in Nepal. China's National Earthquake Networks Center put the magnitude at 6.8; USGS assessed it at Mw 7.1 — a common divergence reflecting different methodology.

The earthquake was caused by normal faulting — extensional tectonics on the Tibetan Plateau, where the plateau is stretching east-west — distinct from the compressive thrust-fault earthquakes typical of the Himalayan front. This distinction is UPSC-significant: the Tibetan Plateau generates extensional earthquakes; the Main Himalayan Thrust generates compressional thrust earthquakes.

While the epicentre was distant from major Indian urban centres, the event reinforced awareness of the Himalayan seismic gap risk — particularly in Uttarakhand and Nepal, which have not experienced a major release event since the 2015 Gorkha earthquake (Mw 7.8).

UPSC angle: Prelims — Tibet earthquake 7 January 2025; Mw 7.1 (USGS)/6.8 (China); Shigatse/Tingri; 126+ deaths; normal faulting (not thrust). Mains (GS3) — Himalayan seismic gap; extensional vs compressional tectonics on the plateau; India's earthquake preparedness.

Myanmar Earthquake — Mw 7.7 (28 March 2025) and the Sagaing Fault

A catastrophic Mw 7.7 earthquake struck near Mandalay, Myanmar, on 28 March 2025, followed 12 minutes later by a Mw 6.4 aftershock (USGS; Wikipedia 2025 Myanmar earthquake). The earthquake was the deadliest seismic event in Asia since the 2023 Turkey-Syria earthquake. Death toll: 3,645+ confirmed as of 8 April 2025, with over 4,817 injured and at least 148 missing (AHA Centre, April 2025); some estimates exceed 5,000 deaths. The worst-affected areas were Mandalay, Sagaing, and Naypyidaw.

The earthquake was caused by right-lateral strike-slip faulting along the Sagaing Fault — a ~1,400 km transform fault running north-south through central Myanmar, resulting from the oblique collision of the Indian Plate with the Eurasian/Sunda plate system. The rupture extended over approximately 400 km (north Mandalay to Pyu) and is classified as a "supershear" event — the rupture velocity exceeded the shear-wave speed, producing exceptionally intense ground shaking (PNAS, 2025; Nature npj Natural Hazards, 2025). At least 415,000 people in Mandalay, Bago, Naypyidaw, and Sagaing regions were exposed to MMI intensity X (USGS PAGER).

The earthquake triggered widespread landslides and liquefaction in unconsolidated sediments along the rupture zone, and caused structural collapse of key landmarks including the historic Mandalay Palace and Innwa (Ava) fort. Three hospitals were destroyed, severely impeding emergency response.

India dimension: India dispatched NDRF teams and relief material under its "Neighbourhood First" humanitarian policy — one of the fastest international responses to the disaster.

UPSC angle: Prelims — Myanmar earthquake: 28 March 2025; Mw 7.7; Sagaing Fault (right-lateral strike-slip); Mandalay; 3,645+ deaths; supershear rupture; 400 km rupture zone. Mains (GS3) — Sagaing Fault tectonics (Indo-Myanmar Arc); strike-slip vs thrust earthquake mechanics; India's humanitarian response; landslide/liquefaction as secondary hazards; relevance to India's northeast seismic risk.

India's New Seismic Map — Updated BIS Hazard Zonation (2024)

The Bureau of Indian Standards (BIS) issued a revised seismic hazard map for India in 2024 — the first major revision since 2002. The updated map uses probabilistic seismic hazard analysis (PSHA), replacing the deterministic approach of earlier versions. Key changes: several areas in Kutch (Gujarat) have been upgraded to higher hazard zones following the 2001 Bhuj aftermath; parts of peninsular India (Deccan plateau) previously considered low-risk have been reclassified to moderate-risk; northeast India's zone V designation reaffirmed with additional granularity.

The updated seismic map is significant for UPSC because it feeds directly into building code requirements (IS 1893), infrastructure planning, and NDMA disaster risk guidelines. States are expected to incorporate the new zonation into their disaster management plans and urban development bylaws.

UPSC angle: Prelims — BIS revised seismic map 2024; PSHA methodology; IS 1893; 5 seismic zones in India. Mains (GS3) — science-policy linkage in disaster risk management; building code enforcement as disaster prevention; peninsular seismicity concerns.

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.
• Root: Ancient Greek seismós (σεισμός) = shaking, earthquake; from seíein = to shake; -ic = adjectival suffix
• Origin: From Ancient Greek seismós (σεισμός, "shaking, earthquake"), from seíein ("to shake") + the suffix -ic; first used in English in the 1850s.
• Part of Speech: adjective
• Word Family: seismology (n), seismologist (n), seismograph (n), seismometer (n), seismicity (n)
• Usage: The simultaneous repeal of three contentious farm laws marked a seismic recalibration of the government's relationship with India's agrarian electorate, reshaping the contours of Centre-State political bargaining for the rest of the term.
• Synonyms: earthquake-related, tectonic, ground-shaking, earth-shaking, momentous, far-reaching
• Antonyms: trivial, negligible, inconsequential, insignificant
• Mnemonic: A SEISMOgraph records earthquakes — so anything SEISMIC literally or figuratively makes the ground shake. Picture a "seismic" headline so big it rattles the room.

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.
• Root: Latin liquēre = to be fluid + facere = to make → liquefacere; Late Latin liquefactiōnem
• 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.
• Part of Speech: noun
• Word Family: liquefy (v), liquefied (adj), liquefying (v pres.p), liquefactive (adj)
• Usage: The 2001 Bhuj earthquake demonstrated that soil liquefaction can transform stable alluvial ground into a treacherous slurry within seconds, underscoring why earthquake-resistant building codes and rigorous geotechnical mapping must anchor India's disaster-management framework in seismically vulnerable zones.
• Synonyms: melting, fusion, liquidisation, dissolution, fluidisation, thawing
• Antonyms: solidification, freezing, congealment, crystallisation
• Mnemonic: "LIQUE-FACT-ion" = Latin liqu(ere) "to be fluid" + fac(ere) "to make" — literally the act of making something fluid; picture solid ground liquefying into a flowing slush in a quake.

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.
• Root: Modern Latin epicentrum (1879); Greek epí = upon, over; kéntron = centre
• Origin: From Modern Latin epicentrum (1879), from Greek epí (ἐπί, "upon, over") + kéntron (κέντρον, "centre"); first used in seismology in 1885.

• Part of Speech: noun
• Word Family: epicentral (adj), epicenters (n pl), hypocentre (n)
• Usage: The national capital became the epicentre of the anti-corruption agitation, with civil-society networks radiating mobilisation outward to district headquarters across the country.
• Synonyms: focal point, nerve centre, focus, heart, hub, core
• Antonyms: periphery, margin, fringe, outskirts
• Mnemonic: "epi-" (upon) + "centre" — the spot upon the surface right over an earthquake's centre; by extension, the centre of any upheaval.

Key Terms

Seismic Zonation

• Definition: Seismic zonation is the division of a country or region into zones of differing earthquake hazard, so that each zone is assigned a design parameter (a seismic "zone factor") reflecting the maximum ground shaking likely there; in India it is mandated by the Bureau of Indian Standards code IS 1893 (Part 1):2016, which classifies the country into four zones, II to V, in increasing order of hazard.
• Context: Seismic zonation is the engineering foundation of earthquake-resistant construction: it translates geological and historical earthquake data into a numeric "zone factor" (Z) that designers feed into building codes. India's first national seismic map was prepared by the Geological Survey of India (1935); the Bureau of Indian Standards (BIS) issued successive maps from 1962 onward, settling on the present four-zone scheme. The current legally applicable map is that of IS 1893 (Part 1):2016. A seventh revision (IS 1893:2025) had added a new highest-risk Zone VI over the Himalayan arc, but it was withdrawn in early 2026 and the 2016 code reinstated.
• UPSC Relevance: This is a foundational concept that underpins UPSC questions on disaster management (GS3), the geography of earthquakes, and institutional bodies like BIS and NDMA. For Prelims, examiners can test the number of zones (four: II-V), which states fall in Zone V, and the agency responsible (BIS, not NDMA). For Mains GS3, it supports answers on earthquake risk reduction, the gap between zoning and enforcement of building codes, and the 2025-26 IS 1893 code revision-and-rollback as a live governance and federalism case study. No verified PYQ exists for this exact term, but it connects directly to the recurring disaster-management and physical-geography question families.

Seismic Microzonation

• Definition: Seismic microzonation is the process of subdividing a region (typically a city) into smaller zones of relatively uniform earthquake hazard, by mapping how local soil, geology and groundwater conditions modify ground shaking, surface peak ground acceleration, soil amplification and liquefaction potential. It produces GIS-based, site-specific hazard maps (in India usually at 1:50,000 regional and 1:10,000 urban scales) that guide earthquake-resilient land-use planning and construction.
• Context: Conventional seismic zoning (macrozonation) under the BIS code IS 1893 divides India into four broad zones (II–V) based on expected intensity — too coarse for city-level planning, since two adjacent sites in the same zone can shake very differently depending on the soil beneath them. Microzonation refines this by adding local site-effect data. In India it is carried out by the National Centre for Seismology (NCS) under the Ministry of Earth Sciences (MoES), which was established in August 2014. Nearly 59% of India's land area lies in moderate-to-high hazard Zones III, IV and V (as per NDMA), making such fine-grained mapping critical for dense urban centres.
• UPSC Relevance: This is a foundational disaster-management concept that underpins GS3 questions on earthquake vulnerability, disaster risk reduction and resilient infrastructure, and links to GS1 physical geography (seismic zones, plate tectonics). Prelims can test factual recall — the nodal body (NCS under MoES), the IS 1893 four-zone framework and the distinction between macrozonation and microzonation. Mains answers on earthquake preparedness, urban planning and the Sendai Framework can use microzonation as a concrete mitigation tool. No verified PYQ exists for this exact term, so treat it as an enrichment concept supporting the broader earthquakes/DRR theme.

Landslide Hazard Zonation

• Definition: Landslide Hazard Zonation (LHZ) is the process of dividing a terrain into zones ranked by their relative susceptibility to landslides, based on causative factors such as lithology, slope, structure, land use and rainfall, so that hazard-prone areas can be identified for planning and mitigation.
• Context: In India, LHZ is governed by Bureau of Indian Standards code IS 14496, with Part 2 (1998) covering macro-zonation and Part 1 (2020) covering meso-zonation, using the Landslide Hazard Evaluation Factor (LHEF) rating scheme. The Geological Survey of India (GSI) is the nodal agency for landslide studies and ran the National Landslide Susceptibility Mapping (NLSM) programme on a 1:50,000 scale. LHZ underpins disaster risk reduction in the Himalayas, the North-eastern hills and the Western Ghats, where landslides cause recurrent loss of life and infrastructure damage.
• UPSC Relevance: This is a foundational GS3 disaster-management concept that underpins questions on landslides, mountain hazards and disaster mitigation. Prelims may test the nodal agency (GSI under the Ministry of Mines), the relevant BIS code, mapping scales, and portals like Bhukosh/Bhusanket. In Mains GS3, it features in answers on disaster vulnerability mapping, early warning systems, and why the Himalayas and Western Ghats are landslide-prone, often linked to climate change and unplanned hill development. No verified PYQ exists for this exact term, so treat it as supporting content for the broader landslides and disaster-preparedness theme.

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.