Earthquake Zonation

New Quake Map Planned

• Bureau of Indian Standards released revised Earthquake Design Code, 2025 (IS 1893), introducing new highest-risk Zone VI and placing the entire Himalayan region under it.
• The updated map places 61% of India’s landmass and 75% of the population under moderate-to-high seismic hazard risk zones. (Earlier, 59% of India’s landmass).
• The previous classification had four seismic zones: Zone II, Zone III, Zone IV, and Zone V. Zone V was earlier the most seismically active, and Zone II the least.
• The Himalayan belt, earlier divided between Zones IV and V, is now placed entirely under Zone VI. This applies from Jammu and Kashmir to Arunachal Pradesh.
• Map is updated using Probabilistic Seismic Hazard Assessment. It considers likelihood & intensity of ground shaking. Revision is based on data on faults, ground-shaking behaviour, tectonic movements, and lithology.
• The revised code lays down standards for both SE design and AEU protection. It aims to reduce damage from ground shaking. The revisions support SDG 9 and SDG 11.

Major Himalayan Fault Systems

• Main Central Thrust (MCT) lies between the Greater Himalayas and Lesser/Middle Himalayas.
• Main Boundary Thrust (MBT) lies between the Lesser Himalayas and Outer Himalayas (Shiwaliks).
• Main Frontal Thrust (MFT) or Himalayan Frontal Fault (HFF) lies between the Outer Himalayas and Northern Indian Plains. HFF is southernmost fault with densely populated foothills.
• The update considers the possibility of southward rupture propagation affecting areas like Dehradun.

Exposure Window and Risk Reduction

• The revised map introduces the concept of an “exposure window”. It considers population density, infrastructure concentration, urban expansion, and socio-economic vulnerability. This uses Probabilistic Exposure and Multi Hazard Assessment method. The approach integrates geological factors with human and economic impacts.

Earthquake Zoning Reverted

• The Centre withdrew the revised earthquake zoning framework after backlash from government departments and infrastructure authorities. BIS had issued a notification to replace IS 1893 (Part 1): 2016.
• The revised notification was withdrawn through a Gazette notification. Objections raised by MoHUA, Metro Rail corporations, and National Dam Safety Authority (NDSA).
• Concerns over increased construction costs due to revised probabilistic seismic hazard assessment (PSHA).
• Over 60% of India’s landmass would fall under moderate to high earthquake risk zones under revised classification.
• Introduction of new highest-risk Zone VI. Parts of Kashmir, North-East and Kutch (Gujarat) placed under highest seismic risk. Himalayan regions categorised under Zone V (very high seismic vulnerability).
• Revised norms would require stronger foundations and structural design changes. MoHUA flagged significant financial implications for infrastructure projects. NDSA raised scientific objections to revised hazard values.