India’s New Seismic Map 2025: Himalayas in Zone VI, Kolkata’s Risk Status Updated
Seismic Zone Map: India has unveiled a radically updated seismic zonation map, marking a historic shift in the country’s disaster preparedness strategy. Under the revised Earthquake Design Code (IS 1893:2025) released by the Bureau of Indian Standards (BIS), a staggering 61% of India’s landmass now falls under moderate to high seismic hazard zones.
The most significant takeaway from this overhaul is the introduction of a new highest-risk category: Zone VI. Previously, India’s seismic zones were capped at Zone V.
Himalayas Under Highest Risk (Zone VI)
The entire Himalayan arc has been placed in the newly created Zone VI. Earlier, this volatile region was split between Zones IV and V. However, consistent tectonic stress and the potential for rupture propagation along the Himalayan Frontal Thrust have led scientists to unify the region under the highest danger category. This change aims to bring much-needed consistency to construction norms in hill states, removing abrupt hazard changes based solely on administrative boundaries.
Status of Kolkata and West Bengal: What You Need to Know
With the introduction of new zones, residents of West Bengal, particularly Kolkata, are concerned about their safety status. Based on the updated guidelines and geographical hazards, here is the breakdown:
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Join on Telegram| Region/City | Seismic Zone (Probable) | Risk Level |
|---|---|---|
| North Bengal (Darjeeling, Jalpaiguri, etc.) | Zone V / VI (Under new classification) | Severe to Extreme Risk |
| Sundarbans Region | Zone IV | High Damage Risk |
| Kolkata & Adjoining Areas | Zone III (Bordering Zone IV) | Moderate to High Risk |
The “Boundary Rule” & Kolkata’s Warning:
Officially, Kolkata remains largely within Zone III (Moderate Damage Risk). However, experts have long argued that due to the city’s soft alluvial soil and high groundwater table—especially in expanding areas like Salt Lake and New Town—the ground motion amplification during a quake can mimic Zone IV intensity.
Crucially, the new code introduces a “Boundary Rule”: any town located on the boundary between two zones is automatically upgraded to the higher-risk category. Given Kolkata’s proximity to the high-risk Sundarbans (Zone IV) and the Bengal Basin’s geological nature, structural engineers are strongly advised to follow Zone IV safety protocols for new high-rises.
stricter Building Codes (IS 1893:2025)
The 2025 edition of the code goes beyond just pillars and beams. It mandates strict safety requirements for non-structural elements:
- Anchoring Mandate: Heavy non-structural elements (like large water tanks, facades, and heavy false ceilings) that exceed 1% of a building’s weight must be securely anchored to prevent internal collapse and injuries.
- Critical Infrastructure: Hospitals, schools, and bridges must be designed to remain functional immediately after a major earthquake, aligning with global resilience standards.
- Soil Liquefaction: For projects near active faults or on soft soil (common in Bengal), the code mandates specific design provisions to account for pulse-like ground motions and soil liquefaction.
This update is a wake-up call for urban planners and home buyers to prioritize compliance over cost, ensuring safety in an increasingly seismically active landscape.
