India Revised Earthquake Design Code, 2025

Context: India has released a radically updated map under the revised Earthquake Design Code (2025), placing the entire Himalayan arc in a newly created highest-risk Zone VI for the first time.

About India Revised Earthquake Design Code, 2025:

What is the Seismic Zonation Map?

• A seismic zonation map classifies different regions of India based on their earthquake hazard potential, helping determine how strong structures must be to withstand earthquakes.

Published by:

• The updated map is issued by the Bureau of Indian Standards (BIS) as part of the revised Earthquake Design Code, 2025 (IS 1893).
• It uses internationally accepted Probabilistic Seismic Hazard Assessment (PSHA)

Key Features of the Revised Zonation Map:

1. Introduction of Highest-Risk Zone VI:

1. • Entire Himalayan arc (J&K–Ladakh to Arunachal) placed in Zone VI, the most hazardous zone, for the first time.
   • Recognises consistent, extreme tectonic stress along the Indian–Eurasian plate boundary.

2. 61% of India Now in Moderate to High Hazard Zones:

1. • A major jump from older estimates relying mainly on past epicentres.
   • Reflects scientific modelling of fault segments, locked sections, and rupture potential.

3. Boundary Towns Auto-Upgraded to Higher-Risk Zone:

1. • If a city lies on the border of two zones, it defaults to the higher-risk one.
   • Moves away from administrative lines to geological realities.

4. Inclusion of Rupture Propagation Southward:

1. • Acknowledges that Himalayan Frontal Thrust ruptures may extend south to populated foothill regions like Dehradun (near Mohand).

5. Mandatory Structural & Non-Structural Safety:

1. • New norms for anchoring parapets, ceilings, tanks, façades, HVAC units, etc., if their weight exceeds 1% of total load.
   • Buildings near active faults must withstand pulse-like ground motions typical of near-fault quakes.

6. New Soil & Ground-Response Requirements:

1. • Detailed provisions for liquefaction, soil flexibility, site-specific shaking spectra.
   • Encourages geotechnical investigations before major construction.

7. Exposure Mapping (PEMA Method):

1. • Incorporates population density, infrastructure concentration and socioeconomic vulnerability.
   • Integrates impact-based assessment with geological hazard.

Significance:

• Improved Earthquake Preparedness: Accurate hazard modelling ensures stronger building codes for at-risk regions, especially the Himalayas.
• Retrofitting Imperative: Old structures, especially in Himalayan towns, must be retrofitted, including schools, hospitals, and bridges.
• Uniformity Across the Himalayan arc Fixes decades of underestimation due to inconsistent older maps (Zones IV & V), despite identical tectonics.