Four zones
Zone II (low) to Zone V (very high), set by the Bureau of Indian Standards.
Zone V share
About 11% of India’s land, including the Himalayan belt and Northeast India.
The real cause
The Indian Plate pushing into the Eurasian Plate, roughly 5 cm every year.
2025-2026 update
A proposed Zone VI was announced, then withdrawn within months.
The Basics
The Four-Zone System
- Set by BIS: India’s seismic zoning, under code IS 1893, sorts the whole country into earthquake-risk zones. The Bureau of Indian Standards (BIS) sets this code.
- Four zones: Zone II is low risk. Zone III is moderate. Zone IV is high. Zone V is very high. This four-tier system covers the entire country.
- Where Zone V sits: it covers the Himalayan belt and all of Northeast India. It also covers parts of Jammu & Kashmir, Uttarakhand, and the Rann of Kutch.
- How the land splits up: about 11% of India’s land falls in Zone V. Another 18% is Zone IV, and 30% is Zone III. The rest is Zone II.
- What decides a zone: BIS looks at each area’s expected peak ground acceleration, how hard and fast the ground is likely to shake in a strong quake, based on nearby fault history. A higher expected shake means a higher zone number.
True or False: India’s seismic zoning system, set by the Bureau of Indian Standards, sorts the country into four risk zones.
The Deeper Cause
Why India Shakes
- A slow collision: the Indian Plate keeps pushing north into the Eurasian Plate, at roughly 5 cm a year. This same collision built the Himalayas, and keeps pushing them higher still.
- Where the stress goes: the two plates don’t slide past each other smoothly. Rock along the boundary bends and locks up, storing the push as stress, like a bent stick that hasn’t snapped yet.
- A very active belt: this ongoing collision makes the Himalayan belt one of the most seismically active places on Earth. It sees around 200 recorded earthquakes every year.
- Seismic gaps: in places, the two plates lock together and slowly build up stress for decades. Scientists call this quiet build-up, before it suddenly releases, a “seismic gap.” When the locked rock finally slips, all that stored stress releases at once, as an earthquake.
Plates Collide
The Indian Plate pushes into the Eurasian Plate, roughly 5 cm a year.
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Rock Locks Up
The boundary doesn’t slide smoothly. Rock bends and stores the push as stress.
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Stress Builds
Over decades, the locked stretch, a “seismic gap,” quietly stores more and more stress.
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Sudden Release
The rock finally slips. Stored stress releases at once, as an earthquake.
Not Just the Himalayas
Cities That Surprise People
- Delhi: falls in Zone IV, despite sitting far from the Himalayan plate boundary. Active fault lines running under the city are the real reason.
- Mumbai: its Konkan coast also falls partly in Zone IV. Another major coastal city carries more risk than its distance from the Himalayas would suggest.
- The lesson: zone assignment tracks actual fault geology, not simple distance from the Himalayan collision. A city can sit far from that boundary and still carry real risk.
True or False: Delhi falls in a low-risk seismic zone because it sits far from the Himalayan plate boundary.
Four Quakes, Four Lessons
Earthquakes That Rewrote the Map
- 1934, Bihar-Nepal: a magnitude-8.0 quake killed over 15,700 people, one of the deadliest in Indian history. It showed just how serious the Himalayan front’s risk really was.
- 1950, Assam: at magnitude 8.6, this was among the largest earthquakes ever recorded on land. Shaking lasted 5 to 6 minutes, with strong aftershocks for months.
- 2001, Bhuj: a magnitude-7.7 quake struck the supposedly stable edge of the Deccan Plateau. It killed over 19,000 people, destroyed more than 400,000 homes, and forced Gujarat’s zoning to be revised upward.
- 2005, Kashmir: a magnitude-7.6 quake near Muzaffarabad killed over 1,360 people on the Indian side. Losses were heavy region-wide. Some school buildings collapsed during class hours.
Think it through. Why did the 2001 Bhuj earthquake, striking a region once considered geologically “stable,” end up reshaping India’s whole zoning approach?
Show the explanation
Before Bhuj, zoning leaned heavily on distance from the active Himalayan plate boundary, since that’s where most well-known quakes struck. Bhuj sits on the Deccan Plateau, far from that boundary. Yet it produced a devastating magnitude-7.7 quake, from a hidden, older fault deep inside the plate. That forced planners to admit one thing: distance from the boundary alone wasn’t a reliable safety signal. Zoning had to follow actual fault geology instead, wherever it’s found.
Preparing for the Next One
Getting Ready for the Next One
- Risk isn’t just Zone V: roughly 59% of India’s land counts as earthquake-prone to some degree. Building-code compliance matters well beyond Zone V alone.
- Retrofitting older buildings: NDMA’s National Retrofitting Programme, launched in 2014, targets older buildings, schools, and hospitals built before today’s earthquake codes.
- Better monitoring: India’s seismic observatory network more than doubled, from 80 stations in 2014 to 168 by 2025. Quakes now get detected faster, and more precisely.
- The nodal agency: the National Center for Seismology (NCS) sits under the Ministry of Earth Sciences. It’s India’s official body for tracking earthquakes nationwide. Its BhooKamp app draws on 152 seismic stations to send real-time alerts.
- Phone-based alerts: Google’s Android Earthquake Alerts System was built with NDMA and NCS. It warns phones automatically for quakes of magnitude 4.5 or above, using phone accelerometers as sensors.
The Real Exam Trap on This Topic
- The trap: options sometimes call the Richter scale an “intensity” scale. It’s actually a magnitude scale, measuring energy released at the source.
- The fix: intensity, how strongly shaking is felt at a place, is measured separately, by the Modified Mercalli scale. Magnitude and intensity are not the same thing.
- CDS-II 2025 Asked whether the Richter scale is an intensity scale (no), and whether it indicates energy released (yes). Each whole-number jump on the Richter scale means roughly 31.6 times more energy released. View CDS-II 2025 Paper, Q91 →
The Reasoning Behind Zoning
Why Zones Exist at All
- The purpose: zoning exists to match building codes to actual local risk, not one national standard everywhere. A Zone II building needs far less earthquake-resistant design than a Zone V one.
- What changes with the zone: a higher zone means stricter rules on materials, structural bracing, and how tall a building can safely go without extra reinforcement. Building in Zone V simply costs more, because the design has to survive stronger shaking.
- It responds to events: zoning revisions after Latur (1993) and Bhuj (2001) show the system reacting to real disasters. It never stays frozen at its original boundaries.
- A wrong assumption, corrected: the 1993 Latur earthquake struck the supposedly stable Deccan Plateau. That forced planners to rethink which “safe” regions truly deserved that label.
Two Kinds of Earthquake
Two Kinds of Earthquake
- Interplate: most Himalayan-belt quakes are interplate. They strike right at the active boundary, where the Indian and Eurasian Plates grind against each other.
- Intraplate: Latur and Bhuj were both intraplate quakes. They struck away from any plate boundary, along older, hidden faults buried inside one continuous plate.
- Why intraplate is tricky: these quakes are harder to predict. The fault causing them isn’t marked by an obvious, well-mapped plate edge. That’s exactly why Latur and Bhuj caught seismologists off guard.
True or False: The Latur and Bhuj earthquakes were interplate quakes, striking right at an active plate boundary.
2025-2026 Update
Zone VI: Proposed and Withdrawn
- The proposal: in November 2025, BIS released IS 1893:2025. It added a new, higher-risk Zone VI across the entire Himalayan arc, with a safety margin above Zone V.
- The cost concern: a Zone VI classification meant stronger, and more expensive, building codes across the Himalayan belt.
- The reversal: in March 2026, BIS withdrew the 2025 code after the Ministry of Housing and Urban Affairs raised construction-cost concerns. The older IS 1893:2016 code came back into force.
- Why it matters: a rollback within months, not years, shows science and construction-cost politics pulling in opposite directions. Expect this episode on current-affairs questions.
Quick Q&A
Q: What causes India’s earthquakes at the deepest level?
A: The Indian Plate pushing into the Eurasian Plate at roughly 5 cm a year, the same collision that built the Himalayas.
Q: Why does Delhi fall in Zone IV, despite being far from the Himalayas?
A: Active fault lines run directly under the city. Zoning tracks real fault geology, not simple distance from the Himalayan boundary.
Q: What’s the difference between the Richter scale and the Modified Mercalli scale?
A: Richter measures magnitude, the energy released at the source. Mercalli measures intensity, how strongly shaking is felt at a place.
Q: What happened to the proposed Zone VI?
A: BIS proposed it in November 2025, then withdrew it in March 2026 over construction-cost concerns, reverting to the older code.
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