What Happened
- India's Bureau of Indian Standards (BIS) released a major revision to IS 1893 (Part 1) — the national earthquake design code — in November 2025, creating a new Zone VI for the entire Himalayan arc and nearly doubling seismic hazard estimates in the region based on a decade of Probabilistic Seismic Hazard Assessment (PSHA) research.
- The revised seismic zonation map was subsequently withdrawn by the government, reportedly due to concerns that higher hazard estimates would significantly increase construction costs for housing, infrastructure, and public buildings in Himalayan and northeastern states.
- The withdrawal is considered scientifically controversial: researchers and seismologists argue the updated hazard estimates reflect real-world risk from the Himalayan collision zone, and that deferring their adoption leaves millions in seismically active areas with inadequately designed structures.
- The previous IS 1893 classification placed most of the Himalayas in Zone IV and Zone V; the withdrawn revision would have reclassified the entire Himalayan arc into a newly created highest-risk Zone VI.
Static Topic Bridges
India's Seismic Zonation and IS 1893
IS 1893 (Criteria for Earthquake Resistant Design of Structures) is the Bureau of Indian Standards' primary code governing how buildings, bridges, dams, and industrial structures must be designed to withstand earthquakes. The code classifies India into seismic zones (Zone II through Zone V under the previous revision; Zone VI proposed in 2025) based on intensity, frequency, and likely maximum earthquake magnitude for each region. Seismic zone classification directly drives the Zone Factor (Z) used in structural calculations — higher zones require stronger foundations, more reinforcement, and more expensive designs. The code is mandated for all public buildings and is referenced in building by-laws across states.
- Previous IS 1893 edition (2016): Zone II (low hazard) to Zone V (very high hazard)
- Zone V already includes: entire northeast India, J&K (parts), Uttarakhand and Himachal Pradesh Himalayan zones, Andaman and Nicobar Islands
- The proposed 7th revision (2025): introduced Zone VI (extreme hazard) covering the entire Himalayan arc; adopted Probabilistic Seismic Hazard Assessment (PSHA) replacing the older deterministic approach
- BIS IS 1893 is a mandatory reference under National Building Code of India 2016
- Himachal Pradesh was to be placed entirely in Zone VI under the 2025 revision
Connection to this news: The government's withdrawal of the Zone VI revision effectively delays compliance with an updated scientific understanding of Himalayan seismic hazard, leaving existing building stock and new construction in the region potentially under-designed.
Himalayan Seismotectonics — Why the Region is High-Risk
The Himalayas are geologically young fold mountains formed by the ongoing collision between the Indian Plate and the Eurasian Plate. This collision, ongoing at approximately 5 cm per year, creates one of the most seismically active zones on Earth. The Main Central Thrust (MCT), Main Boundary Thrust (MBT), and the Himalayan Frontal Thrust (HFT) — also called the Main Frontal Thrust — are the three principal thrust fault systems running parallel to the Himalayan arc. The HFT is considered capable of generating great earthquakes (Magnitude > 8.0) due to accumulated strain from the locked section of the Indian Plate. Historical great earthquakes along this zone include: Kangra 1905 (M 7.8), Bihar-Nepal 1934 (M 8.1), Assam 1950 (M 8.6 — one of the largest 20th-century earthquakes), and more recently Nepal 2015 (M 7.8, affecting India's Uttarakhand and Bihar).
- Indian Plate convergence rate: ~5 cm/year northward against Eurasia
- Seismic gap: the central Himalayan segment (Uttarakhand–Nepal) is identified as a seismic gap — a zone that has not ruptured in 200+ years and is accumulating strain
- Entire northeast India (Arunachal, Assam, Manipur, Meghalaya, Mizoram, Nagaland, Tripura, Sikkim) lies in Zone V or proposed Zone VI
- Indian Ocean 2004 earthquake (M 9.1, Sumatra subduction): demonstrated India's vulnerability to both inter-plate and subduction zone events
- Uttarakhand Disasters: 2013 Kedarnath flood-landslide, 2021 Chamoli rock-ice avalanche — both related to seismically weakened terrain
Connection to this news: The scientific basis for a Zone VI reclassification is precisely the seismic gap theory — the probability that the central Himalayan segment will rupture at Magnitude 8+ within decades, which the withdrawn revision was designed to account for.
National Disaster Management Framework — Institutional Roles
India's disaster management architecture is governed by the Disaster Management Act, 2005. The National Disaster Management Authority (NDMA) under the Prime Minister formulates national policies and guidelines. The National Disaster Response Force (NDRF) is the operational arm. At the state level, State Disaster Management Authorities (SDMAs) implement guidelines. For earthquake preparedness specifically, the National Earthquake Risk Mitigation Project (NERMP) under the Ministry of Housing and Urban Affairs targets seismic retrofitting of existing government buildings and updating state building by-laws. The Sendai Framework for Disaster Risk Reduction 2015–2030 (to which India is a signatory) emphasises prevention over response and explicitly calls for risk-informed building codes.
- NDMA's 2007 Earthquake Risk Mitigation Guidelines require states to adopt IS 1893 in building by-laws
- National Building Code of India (NBC 2016): the umbrella code that references IS 1893 for seismic design
- Seismically vulnerable housing stock: over 45 million rural houses in Zones IV and V are non-engineered — not designed to any code
- Retrofitting cost for a typical masonry building in Zone V: ₹50,000–₹1.5 lakh (vs. ₹5–15 lakh reconstruction cost after collapse)
- Sendai Framework Target B: Reduce the number of affected people by disasters globally by 2030
Connection to this news: The cost concerns cited for withdrawing the code revision directly contradict the Sendai Framework's principle that investment in risk prevention is more cost-effective than post-disaster response.
Probabilistic Seismic Hazard Assessment (PSHA) — The Scientific Advance
Traditional seismic zonation in India used a deterministic approach — identifying the maximum possible earthquake near a site and designing for that scenario. PSHA, the methodology adopted in the withdrawn 2025 revision, quantifies the probability that a given ground shaking intensity will be exceeded within a specific time period (typically 50 years with 10% probability of exceedance). PSHA integrates data from active fault databases, historical seismicity catalogues, ground motion prediction equations, and site-specific soil amplification. The National Seismic Hazard Map of India, developed collaboratively by multiple research institutions over a decade, formed the scientific backbone of the 2025 IS 1893 revision.
- PSHA output: Peak Ground Acceleration (PGA) maps at different return periods (475-year and 2,475-year)
- The new map would have roughly doubled the PGA values assigned to most Himalayan districts
- Countries that have adopted PSHA-based codes: USA (ASCE 7), Japan (BSL), Europe (Eurocode 8), Nepal (NBC 105)
- Bhuj 2001 earthquake (M 7.7, Gujarat): exposed large-scale non-compliance with IS 1893 in existing buildings; triggered the last major revision of the code
Connection to this news: The decade of PSHA research that underpinned the 2025 revision is not invalidated by its withdrawal — the seismic hazard remains; only the regulatory response has been deferred.
Key Facts & Data
- IS 1893 (7th revision, Nov 2025): introduced Zone VI covering entire Himalayan arc; subsequently withdrawn
- Previous IS 1893 (2016, 6th revision): Zones II–V; entire northeast already in Zone V
- Zone V currently covers: J&K (parts), Uttarakhand Himalayas, entire northeast, Andaman and Nicobar
- Nepal 2015 earthquake (M 7.8): killed ~9,000; caused damage in Uttarakhand and Bihar
- Bhuj 2001 earthquake (M 7.7): ~20,000 killed; last major trigger for IS 1893 revision
- Indian Plate convergence rate: ~5 cm/year
- Central Himalayan seismic gap: has not ruptured in 200+ years; capable of M 8.0+
- Non-engineered vulnerable houses in Zones IV–V: 45+ million
- National Building Code 2016 references IS 1893 as mandatory
- Sendai Framework (2015–2030): India is a signatory; emphasises risk-informed building standards