India Earthquake Zoning Reform: BIS PSHA Framework and Seismic Risk Debate

The Union government rolled back the revised earthquake zoning framework proposed by the Bureau of Indian Standards (BIS), amid concerns about the methodology and the cost implications for construction and infrastructure projects.

Limitations of India’s Existing Earthquake Zoning Framework

• Outdated Zoning System: India’s earthquake zoning system, established 30–40 years ago, is considered outdated because it was developed when technology and urbanisation levels were significantly lower.
• Extent of Seismically Active Areas: Under the existing model, about 59% of India’s land area is classified as seismically active.
• Seismic Zoning of India (Earthquake Risk Classification):
  • Zone II (Lowest earthquake risk): largely covering the Deccan Plateau and most of South India.
  • Zone III (Moderate earthquake risk): includes Madhya Pradesh and parts of Maharashtra.
  • Zone IV (High earthquake risk): covers Delhi, parts of Uttar Pradesh, and Mumbai.
  • Zone V (Highest earthquake risk):  includes Kashmir, North-East India, and the Kutch region.
• Lack of Site-specific Assessment: The framework does not incorporate local geological conditions, treating areas with hard rock and soft alluvial soil alike, even though softer soils amplify seismic waves and increase earthquake damage.
• Absence of Probabilistic Assessment: The system treats seismic risk as static rather than incorporating probability and evolving hazard patterns.
• Rigid Classification: Once an area was zoned, it remained fixed with no dynamic recalculation of seismic risk.

Proposed Shift to a Probabilistic Seismic Hazard Assessment (PSHA) Framework

• Adoption of PSHA Model: The Bureau of Indian Standards (BIS) proposed replacing the traditional fixed zoning system with Probabilistic Seismic Hazard Assessment (PSHA), a method widely used in countries such as the U.S. and Japan to estimate earthquake risk more scientifically.
• Use of Historical Seismic Data: The framework analyses earthquake frequency and intensity over the past 500 years to understand long-term seismic patterns.
• Mapping of Tectonic Faults: It incorporates detailed mapping of tectonic plates and underground fault lines to identify regions with higher seismic vulnerability.
• Probability-based Risk Estimation: The model calculates the probability that earthquakes of specific intensities will occur within a future time frame (e.g., the next 50 years).
• Introduction of a New Category: The proposal introduced Zone VI, an “extremely high risk” seismic zone. The areas proposed to be placed in Seismic Zone VI were:
  • Kashmir Valley: Located in the Himalayan collision zone, experiencing frequent tremors.
  • Uttarakhand and Himachal Pradesh: Part of the active Himalayan seismic belt.
  • Kutch Region (Gujarat): Site of the devastating Bhuj earthquake (2001) that caused over 20,000 deaths.
  • Entire North-East India: Falls within an extremely active seismic zone due to complex tectonic interactions.

Reasons for the Rollback of the Probabilistic Seismic Hazard Assessment (PSHA) Framework

• Higher Construction Costs: Upgrading seismic risk zones would mandate stricter structural standards, increasing construction costs by about 20% for one zone upgrade and nearly 33% for two zones.
• Major Infrastructure Retrofitting Burden: Reclassification would require costly strengthening of over 5,700 large dams, metro systems, highways, and other critical infrastructure, potentially costing thousands of crores per project.
• Challenges for the Informal Housing Sector: Since nearly 80% of Indian homes are built informally without professional supervision, higher compliance costs may push households to bypass safety norms altogether.
• Environmental Conflict: Stricter norms require more steel and cement, leading to higher carbon emissions. 
  • This creates a paradox of disaster resilience versus climate mitigation.
• Concerns over Methodological Consistency: Some ministries and experts argued that PSHA outputs did not always align with site-specific ground assessments, raising questions about its reliability for regulatory use.

Way Forward

• Phased Implementation: Government buildings and critical public infrastructure should first adopt stricter seismic safety norms, with standards later extended to private construction.
• Subsidies: Poor and vulnerable households should receive financial support through schemes such as the Pradhan Mantri Awas Yojana (PMAY) to enable the construction of earthquake-resilient housing.
• Hybrid Testing: Bodies such as BIS and engineering institutions should adopt a hybrid approach that combines PSHA with site-specific ground testing to improve the accuracy of risk assessment.
• Construction sector and industry: Builders and material producers should promote low-carbon materials such as fly ash cement and bamboo to align earthquake resilience with climate mitigation.
• Local masons and grassroots builders: Training programmes and earthquake-safe manuals in local languages should be provided to local masons and construction workers to improve compliance with safety standards.

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Conclusion

India’s seismic zoning reform must balance scientific risk assessment with affordability and practical implementation to build a disaster-resilient built environment.

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