Seismic Zonation and Regulatory Changes in India
The seismic zonation in India has undergone significant changes recently, marked by the introduction and subsequent withdrawal of a new seismic code.
Introduction of the New Seismic Code
- The Centre announced a new seismic zonation, introducing an additional Zone 6, covering the entire Himalayan arc in the highest risk zone.
- Almost 60% of Indian land mass was categorized in moderate to high-risk zones.
- The updated seismic code, IS 1893 of 2025, was aimed at enforcing stricter construction and building safety standards.
Withdrawal of the 2025 Code
- Three months after its announcement, the 2025 version of IS 1893 was withdrawn in favor of the 2016 standard.
- The Bureau of Indian Standards (BIS) confirmed the withdrawal through a March 3 gazette notification.
Reasons for Withdrawal
- Stakeholder Consultation: The Ministry of Housing and Urban Affairs (MoHUA) raised concerns about inadequate stakeholder consultation.
- Financial Impact:
- Potential 10%-15% cost hike in Zones VI and V.
- More than 20% cost increase for residential buildings and up to 50% for infrastructure projects.
- Technical Feasibility: Questions arose regarding the feasibility of implementing the mandated standards in Zone VI areas.
- Theoretical Basis: The new zonation was considered too theoretical, given current compliance with seismic construction requirements was already low.
Previous Seismic Zones
India was previously divided into four seismic zones: II, III, IV, and V. The 2025 notification added Zone VI, covering the entire Himalayan arc and upgrading several cities to higher-risk zones.
Safety Features and Implications
- The new code introduced retrofitting requirements for critical infrastructure like hospitals and schools.
- It mandated the strengthening of non-structural elements in buildings and verification of real estate projects for earthquake resistance.
