Seismic Preparedness Leap: Decoding India’s Revised Earthquake Design Code, 2025 (IS 1893:2025)
Seismic Preparedness Leap: Decoding India’s Revised Earthquake Design Code, 2025 (IS 1893:2025)
India’s seismic safety framework underwent a decisive transformation in November 2025 with the release of the revised Earthquake Design Code, IS 1893:2025, by the Bureau of Indian Standards (BIS). This update is not merely a refinement of engineering guidelines, it represents a strategic shift toward a scientifically robust and nationally uniform approach to earthquake risk. The introduction of Zone VI, the new highest-risk category applied across the entire Himalayan arc, fundamentally alters how the country perceives and plans for seismic hazards. The revision aims to realign construction practices, infrastructure policy, and disaster-risk management with the actual tectonic and geotechnical realities of one of the world’s most seismically active regions.
1. Evolution of India’s Seismic Risk Understanding
The journey toward IS 1893:2025 reflects a shift from traditional, reactive hazard assessment to modern predictive modelling. Earlier editions depended heavily on Deterministic Seismic Hazard Assessment (DSHA), which relied on historical earthquake occurrences and maximum-credible earthquake assumptions for a region. While DSHA provided a basic understanding, it could not fully capture the complex and evolving nature of seismicity in a country intersected by multiple active faults.
In contrast, Probabilistic Seismic Hazard Assessment (PSHA), the cornerstone of the revised code which integrates a much wider spectrum of data. PSHA considers fault geometry, rupture behaviour, recurrence intervals, tectonic plate movements, ground-motion predictions, and the statistical probability of shaking intensities across different time frames. This allows engineers to design structures for specific return periods, such as a 2,500-year event, ensuring a quantifiable margin of safety. The adoption of PSHA also harmonises India’s seismic standards with global practices, strengthening both safety and scientific credibility.
2. Redefining Zonation: The New Hierarchy of Seismic Risk
A major outcome of PSHA is the revised Seismic Zonation Map, which reorganises India into five zones: II, III, IV, V, and VI. Unlike previous versions where Zone V represented the highest hazard, the new framework places the most vulnerable areas under Zone VI, a category designed to reflect extreme and persistent tectonic stress.
This change is not cosmetic; it significantly influences the design forces considered during structural analysis. Higher zoning factors translate directly into increased lateral load requirements, stronger foundations, and more advanced engineering interventions. The introduction of Zone VI corrects earlier underestimations and mandates that buildings in these areas adhere to the highest seismic safety thresholds. By establishing a clear hierarchy of risk, the code provides uniform guidance to engineers, policymakers, and urban planners across the country.
3. Himalayan Arc Under Zone VI: A Uniform Recognition of Hazard
One of the most significant features of IS 1893:2025 is the uniform classification of the entire Himalayan arc under Zone VI. The Himalayas, formed by the collision of the Indian and Eurasian plates, are characterised by enormous tectonic strain and complex fault systems, particularly the Main Himalayan Thrust (MHT). Earlier classifications divided this region between Zones IV and V, despite geological evidence showing consistent seismic potential along the entire arc.
The new uniform zoning eliminates these inconsistencies and enforces the strictest design standards from Jammu & Kashmir–Ladakh to Arunachal Pradesh. This ensures that structural safety does not depend on administrative boundaries but on actual geophysical conditions. It also compels state governments and local bodies to upgrade building by-laws and construction practices in line with the highest risk category, reducing the likelihood of catastrophic failures in future earthquakes.
4. Expanded High-Hazard Areas and Boundary Rules
The advanced modelling incorporated in PSHA has led to a more realistic representation of seismic hazard across India. As a result, the proportion of land classified under moderate-to-high hazard categories has increased to 61%, up from around 59%. This shift reflects a more accurate understanding of active fault lines, particularly in regions previously assumed to be relatively stable, such as parts of the Deccan Plateau.
Another notable reform is the introduction of the Boundary Town Rule, which mandates that settlements situated on the edge of two zones must be placed in the higher-risk zone. This eliminates ambiguity and prevents misclassification that could compromise public safety. The rule ensures that construction guidelines err on the side of caution, especially in towns expanding across geological transition zones.
5. Addressing Near-Fault Hazards and Non-Structural Vulnerabilities
The revised code gives unprecedented attention to near-fault effects and non-structural components, which have historically contributed heavily to earthquake-related damage and casualties. Near-fault areas, those located close to active faults, can experience pulse-like ground motions, which are short-duration, high-energy movements capable of placing extraordinary stress on buildings, bridges, and lifelines. Recognising this, the code requires engineers to incorporate design measures such as increased damping, enhanced flexibility, and, where feasible, base isolation systems.
Equally important is the mandatory anchoring of non-structural elements. Items such as parapets, water tanks, false ceilings, and HVAC systems have often collapsed in past earthquakes, causing injuries and complicating rescue operations. Under IS 1893:2025, any non-structural elements exceeding 1% of the building’s total weight must be secured using approved seismic anchorage methods. This requirement directly addresses a major source of casualty risk and enhances overall building performance during ground shaking.
6. Advanced Geotechnical Requirements and Site-Specific Design
IS 1893:2025 goes beyond zonation and mandates site-specific geotechnical investigations, recognising that soil behaviour greatly influences earthquake damage. The code includes detailed provisions for:
- Liquefaction assessment, identifying areas where water-saturated soils may lose strength during shaking.
- Site-specific response spectra, ensuring that structural design reflects local soil profiles rather than generic assumptions.
- Design for pulse-type motions, especially near active faults, demanding specialized analysis for tall buildings, long-span bridges, and critical infrastructure.
These requirements ensure that buildings are designed not only according to general hazard categories but also to the unique ground conditions of their locations.
7. Implications for Infrastructure, Governance, and Community Safety
The impact of IS 1893:2025 extends far beyond engineering calculations. The updated code signals a national commitment to resilient infrastructure and proactive disaster management. Its emphasis on PSHA aligns India’s seismic preparedness with its actual tectonic context, reducing long-term vulnerability and economic losses.
A major policy implication is the requirement to retrofit critical infrastructure, including hospitals, schools, emergency facilities, and bridges. These structures must remain functional immediately after a major earthquake to facilitate rescue, medical care, and public sheltering. Furthermore, by integrating aspects of population density and socioeconomic vulnerability similar to multi-hazard assessment frameworks, the code ensures that seismic risk evaluation reflects not only the physical hazard but also the potential human impact.
The revision also encourages better urban planning, stricter enforcement of building by-laws, and widespread adoption of earthquake-resilient construction techniques. Ultimately, IS 1893:2025 marks a decisive leap toward a safer built environment, strengthening India’s long-term resilience and setting a new standard in national disaster-risk reduction efforts.