Topic 6: Vulcanicity & Earthquakes in India
India sits astride one of Earth's most active collision zones — the Indian plate driving north into Eurasia — making earthquakes a first-order hazard for the Himalaya, the plains and even parts of the "stable" peninsula. This chapter builds the physics first (vulcanicity, earthquake mechanics, focus & epicentre, seismic waves, magnitude vs intensity), then applies it to India: the Deccan-Trap volcanic record, the live volcanoes of the Andaman arc (Barren & Narcondam), the BIS seismic-zone map (Zones II–V), the great Indian earthquakes (Bhuj, Latur, Kashmir, Sikkim), reservoir-induced & intraplate seismicity, the 2004 tsunami, and disaster mitigation. With labelled diagrams, tables and PYQs + full model answers.
On this page
- 1.India's Seismotectonic Setting — Overview
- 2.Vulcanicity & India's Volcanic Record
- 3.Present Volcanoes: Barren & Narcondam
- 4.Earthquake Mechanics: Focus, Waves, Magnitude
- 5.Why India is Earthquake-Prone
- 6.Seismic Zoning of India (Zones II–V)
- 7.Major Indian Earthquakes
- 8.Intraplate & Reservoir-Induced Seismicity
- 9.Tsunami & the 2004 Indian Ocean Event
- 10.Impacts, Mitigation & GS-III Synthesis
- 11.Current Affairs Link
- 12.Prelims PYQs
- 13.Mains PYQs + Model Answers
- ★15-Minute Revision Box
Conceptual Clarity — Why this Chapter Matters
This is a cross-over chapter — Prelims tests the definitions, Mains (GS-III) tests disaster management. Sort your prep three ways:
- Definitional / static: focus (hypocentre) vs epicentre; body waves (P, S) vs surface waves (L); P = fastest & through solid+liquid, S = only through solids (reveals the liquid outer core); magnitude (Richter/moment, energy) vs intensity (Mercalli, damage); Barren = only active volcano.
- Statement-elimination: seismic Zones II–V (V = highest risk: NE, Kashmir, Kutch, Andaman), Bhuj 2001 (intraplate, Kutch), Latur 1993 & Koyna 1967 (peninsular/reservoir-induced), 2004 tsunami source (Sumatra subduction).
- Applied / synthesis (Mains GS-III): why the Himalaya & Kutch are so seismic (plate convergence), why "stable" peninsula still quakes, building-code & early-warning gaps, NDMA & the tsunami-warning system. Needs cause + example + policy.
Territorial note: the seismic zones described cover the entire sovereign territory of India, including Jammu & Kashmir, Ladakh and the Andaman & Nicobar Islands. The LoC and LAC are not settled international borders.
1. India's Seismotectonic Setting — Overview
Earthquakes and volcanoes are endogenic (internal-force) phenomena driven by plate tectonics. India's hazard profile flows from one master fact: the Indian plate is moving north-north-east at ~5 cm/yr and colliding with the Eurasian plate, building the Himalaya and storing vast crustal strain.
- Convergent margin: the Indian plate underthrusts the Eurasian plate along the Himalaya — a continent–continent collision generating shallow, damaging quakes.
- Subduction margin: off the Andaman–Sumatra arc the Indian plate subducts, producing volcanoes (Barren, Narcondam) and great tsunamigenic quakes (2004).
- Intraplate stress: even the rigid peninsula carries ancient rift faults (Narmada–Son, Godavari) that occasionally rupture (Latur, Koyna).
2. Vulcanicity & India's Volcanic Record
Vulcanicity is the movement of molten rock (magma) into or onto the crust. India today has very little active volcanism on the mainland — but its geological past holds one of Earth's greatest volcanic events.
2.1 Types (quick recap)
- Intrusive (plutonic): magma cools within the crust → batholiths, dykes, sills, laccoliths.
- Extrusive (volcanic): lava reaches the surface → central-vent cones or, as in India, vast fissure flows.
2.2 India's volcanic record
- Deccan Traps: around 66 Ma, enormous fissure eruptions of basaltic lava covered ~5 lakh km² of west-central India — one of the largest volcanic provinces on Earth; source of black regur soil and step ("trap") topography.
- Rajmahal Traps: older (Jurassic–Cretaceous) basalt flows in the east (Jharkhand–Bengal).
- Present-day: active volcanism is confined to the Andaman arc (Barren, Narcondam) — not the mainland.
3. Present Volcanoes: Barren & Narcondam
India's only volcanoes are in the Andaman Sea, on the Indian–Burmese subduction arc — an extension of the Indonesian volcanic belt.
| Volcano | Status | Note |
|---|---|---|
| Barren Island | Active (India's only active volcano) | Andaman Sea; erupted repeatedly (incl. recent decades); uninhabited |
| Narcondam | Dormant | Andaman Sea; forested; Narcondam hornbill endemic |
4. Earthquake Mechanics: Focus, Waves & Magnitude
An earthquake is the shaking of the ground from a sudden release of accumulated crustal strain (elastic-rebound theory) — usually along a fault.
4.1 Focus & epicentre
- Focus (hypocentre): the point inside the Earth where rupture begins; shallow-focus quakes are the most damaging.
- Epicentre: the point on the surface directly above the focus; shaking is strongest here.
4.2 Seismic waves
| Wave | Type | Key property |
|---|---|---|
| P-wave (Primary) | Body, longitudinal | Fastest; travels through solids, liquids & gases |
| S-wave (Secondary) | Body, transverse | Slower; travels only through solids (reveals the liquid outer core — S-wave shadow zone) |
| L-wave (Surface) | Surface (Love/Rayleigh) | Slowest but most destructive; confined to the surface |
4.3 Magnitude vs intensity
- Magnitude = energy released; measured on the Richter / moment-magnitude scale (logarithmic) — a single value per quake.
- Intensity = degree of shaking/damage felt; measured on the Modified Mercalli scale — varies with distance & ground.
5. Why India is Earthquake-Prone
About 59% of India's land is prone to moderate-to-severe earthquakes — a consequence of active tectonics on three fronts.
- Himalayan collision belt: continuous strain from the plate collision → frequent shallow quakes (Uttarkashi 1991, Kashmir 2005, Nepal 2015 felt across N. India).
- Kutch & western margin: ancient rift & the Kutch fault system → great intraplate quakes (Bhuj 2001).
- Andaman–Nicobar subduction: plate subduction → volcanoes & tsunamigenic mega-quakes (2004).
- Peninsular rift faults: Narmada–Son, Godavari, Koyna → occasional damaging intraplate/reservoir-induced quakes (Latur 1993, Koyna 1967).
- Soft-soil amplification: the thick alluvium of the plains amplifies shaking, raising damage far from the epicentre.
6. Seismic Zoning of India (Zones II–V)
The Bureau of Indian Standards (BIS) divides India into four seismic zones — II, III, IV and V (an older map had five; Zone I was merged into II) — in rising order of expected intensity. There is no Zone I today.
| Zone | Risk | Representative areas |
|---|---|---|
| Zone V | Very high (highest) | NE India, Kashmir–Himalaya, Kutch (Gujarat), N. Bihar, Andaman & Nicobar |
| Zone IV | High | Delhi-NCR, remaining Himalayan foothills, parts of Indo-Gangetic plain, Sikkim |
| Zone III | Moderate | Much of the peninsula fringe, central India, coastal belts |
| Zone II | Low | Most of the stable peninsular interior |
- Zone V (most dangerous): the entire NE, Kashmir Himalaya, the Kutch (Rann) region, parts of north Bihar and the Andaman & Nicobar Islands.
- Delhi lies in Zone IV — a high-risk mega-city on soft Yamuna alluvium.
- The zoning is based on past seismicity, tectonics and expected ground motion — it drives the earthquake-resistant building codes (IS 1893).
7. Major Indian Earthquakes
A handful of quakes recur in exams — learn the year, place, tectonic type and one lesson for each.
| Earthquake | Year | Type / setting | Lesson |
|---|---|---|---|
| Assam–Tibet | 1950 | Himalayan collision (great quake, M~8.6) | Brahmaputra course changes; NE hazard |
| Koyna | 1967 | Peninsular — reservoir-induced | Dams can trigger quakes (RIS) |
| Uttarkashi | 1991 | Himalayan (Uttarakhand) | Hill building vulnerability |
| Latur (Killari) | 1993 | Peninsular intraplate (Maharashtra) | "Stable" shield can rupture; heavy toll |
| Bhuj | 2001 | Intraplate, Kutch fault (Gujarat) | Great intraplate quake; building codes overhauled |
| Kashmir (Muzaffarabad) | 2005 | Himalayan collision | Cross-border relief; landslides |
| Sikkim | 2011 | Himalayan | NE Zone-V risk to hydropower |
| Nepal (Gorkha) | 2015 | Himalayan collision | Felt across N. India; regional exposure |
8. Intraplate & Reservoir-Induced Seismicity
Most quakes occur at plate boundaries, but India also suffers intraplate quakes deep inside the "stable" peninsula, and human-triggered reservoir-induced seismicity.
- Intraplate seismicity: reactivation of ancient rift faults (Narmada–Son, Godavari) — e.g. Latur 1993 — rare but shallow and destructive because they strike unprepared regions.
- Reservoir-induced seismicity (RIS): the weight of a large reservoir + water seepage lubricating faults can trigger quakes — the classic case is Koyna 1967 (Maharashtra), one of the world's best-documented RIS events.
9. Tsunami & the 2004 Indian Ocean Event
A tsunami is a series of long-wavelength sea waves generated by the sudden vertical displacement of the sea floor — usually by a submarine subduction earthquake (also by undersea landslides or volcanic collapse).
- 2004 Indian Ocean tsunami: triggered by a great (M~9.1) subduction quake off Sumatra; devastated the Andaman & Nicobar Islands and the Tamil Nadu–Andhra–Kerala coasts.
- Why coasts are exposed: low, flat, densely-settled east coast (Coromandel) and the near-source A&N islands took the worst impact.
- Response: India set up the Indian Tsunami Early Warning Centre (ITEWC) at INCOIS, Hyderabad, plus coastal bio-shields (mangroves) and preparedness drills.
10. Impacts, Mitigation & GS-III Synthesis
Earthquakes cannot be predicted or prevented — so the entire strategy is risk reduction: know the hazard, build for it, and prepare communities.
- Structural mitigation: earthquake-resistant design (IS 1893, IS 13920), retrofitting, ductile detailing, enforcing building bye-laws — especially in Zones IV–V.
- Non-structural: microzonation of cities (Delhi, Guwahati), land-use control on soft soils, insurance, and public awareness/mock drills.
- Institutional: the Disaster Management Act, 2005 and NDMA (with SDMAs/DDMAs); NDRF for response; early-warning for tsunamis (INCOIS).
- Ecological: mangrove/coral "bio-shields" reduce tsunami & surge energy on the coast.
11. Current Affairs & Contemporary Relevance (2024–2026)
Seismic risk stays "current" through Himalayan quakes, dam-safety debates, microzonation and warning-system upgrades — verify the latest status. check for latest update or data
11.1 Himalayan & regional seismicity
11.2 Dam safety & RIS
11.3 Warning & preparedness
11.4 Why it matters
| Development | Why it matters for UPSC |
|---|---|
| Joshimath subsidence / hill hazards | Himalayan fragility & disaster link (GS-I & GS-III). |
| Dam Safety Act, 2021 | Reservoir-induced seismicity & ageing dams. |
| City microzonation | Urban earthquake risk (Delhi Zone IV). |
| INCOIS tsunami warning | Coastal preparedness after 2004. |
Recurring exam hooks:
- Focus/epicentre · P/S/L waves · magnitude vs intensity (evergreen Prelims).
- Seismic zones · Barren volcano · Bhuj/Latur/Koyna (favourite factual sets).
- Disaster mitigation, NDMA, building codes, tsunami warning (evergreen Mains GS-III).
12. Prelims PYQs (exam-style, high-frequency themes)
Objective questions anchored to genuinely tested UPSC themes on vulcanicity, earthquakes and seismic zoning in India. Each carries a worked rationale.
Q: The point on the Earth's surface directly above the focus of an earthquake is called the:
Answer: (a) Epicentre. The focus (hypocentre) is the underground rupture point; the epicentre is directly above it on the surface, where shaking is strongest.
Q: Which seismic waves cannot pass through the liquid outer core, thereby proving its liquid state?
Answer: (b) S-waves (transverse) cannot travel through liquids — the resulting S-wave shadow zone proves the outer core is liquid. P-waves (fastest) pass through solids and liquids.
Q: India's only active volcano is:
Answer: (b) Barren Island (Andaman Sea) is India's only active volcano. Narcondam is dormant; Baratang has mud volcanoes (not true lava volcanoes).
Q: How many seismic zones does the current BIS map divide India into?
Answer: (b) Four zones (II–V); the erstwhile Zone I was merged into Zone II, so there is no Zone I. Zone V is the highest risk.
Q: Consider the following statements about seismic Zone V:
1. It is the highest-risk zone.
2. The Kutch region of Gujarat lies in it.
3. Most of the peninsular interior falls in it.
Which are correct?
Answer: (a) 1 and 2 only. Zone V is highest-risk and includes Kutch, NE India, Kashmir Himalaya, N. Bihar & A&N. The stable peninsular interior is mostly Zone II (low), not V.
Q: The Koyna earthquake (1967) is a classic example of:
Answer: (b) Koyna is one of the world's best-documented cases of reservoir-induced seismicity — the reservoir's load and water seepage triggered fault movement in the peninsula.
Q: The 2004 Indian Ocean tsunami was generated by a great earthquake off the coast of:
Answer: (b) The M~9.1 subduction quake off Sumatra triggered the tsunami that struck the A&N Islands and India's east coast. Tsunamis need vertical sea-floor displacement, typical of subduction quakes.
Q: Which pair is correctly matched (earthquake — setting)?
Answer: (b) Bhuj 2001 was a great intraplate quake on the Kutch fault. Latur = peninsular intraplate; Koyna = reservoir-induced; Kashmir 2005 = Himalayan collision.
Likely: focus vs epicentre · P/S/L waves & shadow zones · magnitude (Richter) vs intensity (Mercalli) · four seismic zones & Zone-V areas · Barren active volcano · Deccan/Rajmahal traps · Bhuj/Latur/Koyna settings · RIS · 2004 tsunami source & INCOIS · ~59% of India seismic. check for latest update or data
13. Mains PYQs + Model Answers
Genuine UPSC GS-I/GS-III themes on India's seismicity, vulcanicity and disaster management. Each carries a full answer skeleton — Introduction → body → Conclusion.
Q: Explain why India is highly prone to earthquakes and how the seismic-zone map reflects this.
Model Answer
- Introduction: nearly 59% of India is quake-prone — a direct result of the Indian plate's northward collision with Eurasia.
- Causes: the Himalayan collision belt (shallow quakes), the Kutch rift (Bhuj), Andaman subduction (tsunamigenic quakes), peninsular rift faults (Latur, Koyna) and soft-soil amplification in the plains.
- Zone map: BIS Zones II–V grade this risk — Zone V (NE, Kashmir, Kutch, N. Bihar, A&N) is highest, Zone II the peninsular interior; the map drives building codes.
- Implication: high-risk zones coincide with dense settlement (Himalayan towns, Delhi, Kutch), so exposure is severe.
- Conclusion: the zone map translates tectonics into planning — making enforcement of zone-based codes the key to cutting risk.
Q: "Earthquakes cannot be predicted, but disasters can be prevented." Discuss with reference to India's mitigation framework.
Model Answer
- Introduction: seismic prediction remains scientifically elusive, so India's strategy centres on risk reduction, not forecasting.
- Structural mitigation: earthquake-resistant design (IS 1893/13920), retrofitting of schools/hospitals, and enforcement of building bye-laws in Zones IV–V.
- Non-structural: city microzonation, land-use control on soft soils, insurance and community mock-drills.
- Institutional: the Disaster Management Act 2005, NDMA/SDMA/DDMA, NDRF for response, and INCOIS tsunami early-warning — much of it catalysed by Bhuj 2001 and the 2004 tsunami.
- Conclusion: the hazard is fixed by nature but the disaster is shaped by preparedness — enforcement and awareness, not prediction, save lives.
Q: Although the Peninsular Plateau is considered stable, it is not free from seismic activity. Examine.
Model Answer
- Introduction: the peninsula is an ancient rigid shield, generally aseismic — yet it has produced damaging quakes, showing "stable" is relative.
- Intraplate faults: ancient rift zones (Narmada–Son, Godavari) can reactivate — Latur 1993 struck an unprepared shield region with heavy casualties.
- Reservoir-induced: large dams add load and pore-pressure that can trigger quakes — Koyna 1967 is a global reference case.
- Consequence: because these areas assumed safety, buildings were unprepared, magnifying damage — a lesson for peninsular cities & dams.
- Conclusion: intraplate and reservoir-induced seismicity mean the whole country, not just the Himalaya, needs seismic-safe construction.
Q: Discuss the causes and consequences of tsunamis in the Indian context, with reference to the 2004 event.
Model Answer
- Introduction: tsunamis are long sea waves from sudden vertical sea-floor displacement, usually by great subduction earthquakes.
- 2004 causes: an M~9.1 subduction quake off Sumatra uplifted the sea floor, sending waves across the Indian Ocean.
- Consequences for India: the near-source A&N Islands and the low, densely-settled Tamil Nadu–Andhra coasts suffered massive loss of life and property.
- Response & lessons: India built the INCOIS/ITEWC warning centre, promoted mangrove bio-shields, coastal zoning and preparedness drills.
- Conclusion: tsunami risk is concentrated on subduction-facing coasts — early warning, ecological buffers and coastal planning are the core defences.
Q: Bring out the significance of the Deccan Trap volcanism in India's physical geography.
Model Answer
- Introduction: around 66 Ma, vast fissure eruptions built the Deccan Trap, one of Earth's largest volcanic provinces.
- Soils: weathered basalt yields fertile, moisture-retentive black regur — the base of the cotton belt.
- Relief: horizontal lava sheets created the flat-topped, step-like ("trap") plateaus and Ghat escarpments.
- Conclusion: a single volcanic episode still shapes India's soils, relief and agriculture across a sixth of the country.
Likely: why India is quake-prone & the zone map · prediction vs mitigation (NDMA) · peninsular/intraplate & RIS seismicity · tsunami causes & 2004 · Deccan Trap significance · Himalayan hill-hazard & hydropower risk. check for latest update or data
15-Minute Revision Box
Must-Remember Facts — Vulcanicity & Earthquakes
- Focus = underground rupture; Epicentre = surface point above
- P-wave = fastest, through solid+liquid; S-wave = solids only (liquid-core proof)
- L-wave = surface, most destructive
- Magnitude (Richter) = energy; Intensity (Mercalli) = damage
- Deccan Trap ~66 Ma fissure basalt → regur soil
- Rajmahal Traps (older, east)
- Barren = only active volcano; Narcondam dormant
- Four zones II–V (no Zone I); V = highest
- Zone V = NE, Kashmir, Kutch, N. Bihar, A&N
- Delhi = Zone IV; ~59% of India seismic
- Bhuj 2001 = intraplate (Kutch) → DM Act 2005/NDMA
- Latur 1993 = peninsular intraplate
- Koyna 1967 = reservoir-induced (RIS)
- 2004 tsunami = Sumatra subduction; INCOIS warning