01.12.2025

India Revises Earthquake Design Code, 2025 (IS 1893:2025)

Context

India released an updated Seismic Zonation Map in November 2025 under the revised Earthquake Design Code (IS 1893:2025). The major highlight is the creation of a new highest-risk Zone VI, covering the entire Himalayan arc. This brings a significant shift in the country’s seismic preparedness and structural safety framework.

About the Code

The revised earthquake design code issued by the Bureau of Indian Standards (BIS) marks a transition from earlier, damage-based assessments to modern, scientific, data-driven seismic modelling.

Seismic Zonation Map: The New Zones

Purpose

• Categorises India into zones based on earthquake hazard potential.
   
• Guides mandatory structural design standards to enhance seismic resilience.
   

Methodology

The new map is based on Probabilistic Seismic Hazard Assessment (PSHA), which includes:

• Detailed fault modelling and rupture potential
   
• Ground-shaking behaviour
   
• Tectonic regime analysis
   
• Statistical estimates of ground-motion likelihood
   

New Zones

• Zone VI is introduced as the highest hazard category (earlier the top zone was Zone V).
   
• India is now divided into five zones: II, III, IV, V, VI.
   

Key Features of the Revised Zonation

1. New Zone VI Classification

• The entire Himalayan arc from Jammu & Kashmir – Ladakh to Arunachal Pradesh is uniformly placed in Zone VI.
   
• Corrects earlier inconsistencies where some segments were classified under Zone IV or V despite equal tectonic stress.
   
• Reflects the extreme strain at the Indian–Eurasian plate boundary.
   

2. Increased High-Hazard Coverage

• 61% of India’s land area is now mapped under moderate to high seismic hazard zones (previously ~59%).
   
• This reflects improved scientific modelling of active fault systems.
   

3. Boundary Town Rule

• Any town/city located on the boundary between two zones is automatically placed in the higher-risk zone.
   
• Ensures safety planning based on geological risk rather than administrative borders.
   

4. Rupture Extension Considered

• The code accounts for the possibility that major Himalayan faults may rupture southwards, impacting densely populated foothill regions (e.g., near Dehradun).
   
• Incorporates long-distance ground-shaking effects.
   

5. Non-Structural Safety Mandate

• Requires anchoring of non-structural components such as:
   
  • Parapets
     
  • Water tanks
     
  • False ceilings
     
  • HVAC units
     
• Mandatory if their weight exceeds 1% of total building load, addressing a major cause of injuries during earthquakes.
   

6. Advanced Geotechnical Checks

The revised code mandates:

• Detailed soil liquefaction assessment
   
• Site-specific response spectra
   
• Provisions for structures near active faults
   
• Design measures for pulse-like ground motions commonly occurring close to epicentres
   

Significance of the Revised Code

1. Enhanced Preparedness

• The adoption of PSHA and Zone VI aligns India’s building regulations with actual tectonic stress, especially in the Himalayan region.
   

2. Uniform Risk Assessment

• Uniform classification of the Himalayan belt removes earlier underestimations linked to long-dormant or “locked” fault segments.
   

3. Improved Infrastructure Resilience

• Mandates retrofitting of critical facilities—schools, hospitals, bridges—and ensures newly designed structures must remain operational after a major earthquake.
   

4. Focus on Impact (PEMA Method)

• The updated zoning also incorporates population density and socioeconomic vulnerability.
   
• Ensures that seismic risk assessment reflects not just the hazard, but the potential human and economic impact.