Source: TOI
Context:
- India released a radically updated seismic zonation map under the revised Earthquake Design Code (IS 1893:2025).
- Entire Himalayan arc (J&K–Ladakh to Arunachal Pradesh) placed in a newly created highest-risk Zone VI, reflecting extreme tectonic stress for the first time.
Publishing Authority:
- Bureau of Indian Standards (BIS)
- Methodology: Probabilistic Seismic Hazard Assessment (PSHA) based on international standards
Key Features of the Revised Seismic Zonation Map
- Zone VI – Highest Risk:
- Entire Himalayan arc classified as Zone VI, recognizing consistent tectonic stress along the Indian–Eurasian plate boundary.
- Wider Hazard Coverage:
- 61% of India now falls under moderate to high seismic hazard zones, reflecting scientific modelling rather than just past earthquake epicentres.
- Boundary Towns Upgrade:
- Cities on the boundary of two zones automatically assigned the higher-risk zone, emphasizing geological realities over administrative boundaries.
- Rupture Propagation Southwards:
- Himalayan Frontal Thrust ruptures may extend south to foothill regions like Dehradun, influencing design codes there.
- Mandatory Structural & Non-Structural Safety:
- Anchoring of parapets, ceilings, tanks, façades, HVAC units if weight exceeds 1% of total load.
- Buildings near active faults must resist pulse-like ground motions typical of near-fault earthquakes.
- Soil & Ground Response Requirements:
- Detailed provisions for liquefaction, soil flexibility, site-specific shaking spectra.
- Encourages geotechnical investigations before major construction.
- Exposure Mapping – PEMA Method:
- Integrates population density, infrastructure concentration, and socioeconomic vulnerability.
- Focus on impact-based hazard assessment, linking geological hazard with societal exposure.
