BharatNotes What is Seismic Zonation?
Seismic zonation is the process of dividing a territory into zones of differing earthquake hazard, each assigned a design value that quantifies the strongest ground shaking structures must be built to withstand. In India it is governed by the Bureau of Indian Standards (BIS) code IS 1893 (Part 1):2016, which classifies the country into four zones — II, III, IV and V — in ascending order of risk. (Zones 0 and I from older maps were merged into Zone II.) Each zone carries a "zone factor" (Z) used in the design formula for the horizontal seismic coefficient.
Key Features (IS 1893:2016)
| Zone | Hazard level | Zone factor (Z) | Approx. area of India | Indicative regions |
|---|---|---|---|---|
| V | Very severe | 0.36 | ~11% | NE India, Kashmir Valley, Himachal, Uttarakhand, Rann of Kutch, Andaman & Nicobar |
| IV | Severe | 0.24 | ~18% | Delhi-NCR, parts of Bihar, J&K, Sikkim, Konkan |
| III | Moderate | 0.16 | ~30% | Much of peninsular coast, Kerala, parts of Maharashtra |
| II | Low | 0.10 | Remainder | Stable peninsular/Deccan interior |
The zones broadly correspond to MSK (Medvedev-Sponheuer-Karnik) intensities of VI or less, VII, VIII and IX-and-above for Zones II to V respectively. Together, roughly 59-60% of India's land area lies under moderate-to-high seismic hazard.
Evolution of the Map
- 1935: Geological Survey of India publishes the first hazard map (three zones).
- 1962 onward: BIS issues seismic maps under IS 1893; versions over the years used six, seven and then five/four-zone schemes.
- 2002: The four-zone (II-V) scheme is consolidated.
- 2016: IS 1893 (Part 1):2016 becomes the prevailing standard.
Current Status: The 2025 Revision and Rollback
In November 2025, BIS notified a seventh revision, IS 1893 (Part 1):2025, which added a new highest-risk Zone VI spanning the entire Himalayan arc from Jammu & Kashmir to Arunachal Pradesh and upgraded several cities. However, the Ministry of Housing and Urban Affairs flagged inadequate stakeholder consultation and steep cost escalation (an estimated 10-15% for buildings in Zones V-VI and up to ~50% for some infrastructure). Through a gazette notification dated 3 March 2026, BIS withdrew the 2025 code and reinstated IS 1893 (Part 1):2016 as the applicable standard. So, as of June 2026, India officially has four seismic zones, not six.
UPSC Angle
For Prelims, remember: four zones (II-V), Zone V is the most active, and BIS (under the Department of Consumer Affairs) — not NDMA — frames the zonation. For Mains GS3, the topic anchors discussions on disaster risk reduction, weak enforcement of earthquake-resistant building bye-laws by States, and the 2025-26 revision episode as a study in evidence-based regulation versus stakeholder and cost pressures.
