Model Answer
0 min readIntroduction
Seismic zonation is the process of dividing an area into zones with different levels of potential seismic hazard, based on the probability of experiencing earthquakes of a certain magnitude. It is a crucial component of disaster risk reduction, informing building codes, land-use planning, and emergency preparedness. India, being situated in a highly seismic zone, has been actively involved in seismic zonation since the 1960s. The most recent modification to the seismic zonation map of India was released in 2020 by the National Disaster Management Authority (NDMA), updating the previous map from 2002, and incorporating new data and advancements in seismological understanding. This revised map aims to provide a more accurate assessment of earthquake vulnerability across the country.
Evolution of Seismic Zonation in India
The initial seismic map of India was prepared in 1966-67 by the Geological Survey of India (GSI). This was followed by revisions in 1970, 1980, 1993, and 2002. The 2002 map, based on the Bureau of Indian Standards (BIS) code IS 1893:2002, divided India into five seismic zones – II, III, IV, and V, with Zone V being the most seismically active. The 2020 modification, however, brought significant changes.
Methodology and Changes in the 2020 Map
The 2020 map was developed by a committee constituted by the NDMA, incorporating data from the National Geophysical Data Centre (NGDC), GSI, and other research institutions. The key changes include:
- Increased Granularity: The map provides a more detailed and granular assessment of seismic hazard, considering local site conditions and microzonation.
- Probabilistic Seismic Hazard Assessment (PSHA): The map utilizes PSHA, a more sophisticated method than the deterministic approach used previously, to estimate the probability of exceeding certain ground motion levels.
- Incorporation of New Data: The map incorporates data from recent earthquakes, including the 2015 Nepal earthquake, and improved geological and geophysical data.
- Zone Reclassification: Some areas were reclassified based on the updated hazard assessment. For example, parts of North-East India were upgraded to Zone V.
Seismic Zones in India (2020)
The 2020 map identifies the following seismic zones:
| Zone | Intensity | Area Coverage |
|---|---|---|
| Zone V | Very High | North-Eastern India, parts of Gujarat, Bihar, Delhi, and Andaman & Nicobar Islands |
| Zone IV | High | Parts of Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Sikkim, West Bengal, Rajasthan, and Maharashtra |
| Zone III | Moderate | Coastal regions of India, including Kerala, Goa, and parts of Tamil Nadu |
| Zone II | Low | Remaining parts of India |
Implications for Disaster Management
The modified seismic zonation map has significant implications for disaster management:
- Building Codes: The map informs the revision of building codes (IS 1893) to ensure structures are designed to withstand the expected ground motion in different zones.
- Land-Use Planning: It guides land-use planning, discouraging construction of critical infrastructure in high-hazard zones.
- Emergency Preparedness: It helps in developing targeted emergency preparedness plans and resource allocation.
- Risk Assessment: It provides a basis for conducting detailed risk assessments at the local level.
Limitations
Despite its advancements, the 2020 map has limitations:
- Microzonation: The map provides macro-level zonation and lacks detailed microzonation, which is crucial for site-specific hazard assessment.
- Data Gaps: Data gaps in some regions, particularly in remote areas, can affect the accuracy of the map.
- Dynamic Nature: Seismic hazard is dynamic, and the map needs to be updated periodically to reflect new data and understanding.
Conclusion
The modified seismic zonation map of India (2020) represents a significant step forward in understanding and mitigating earthquake risk. By incorporating updated data and advanced methodologies, it provides a more accurate assessment of seismic hazard across the country. However, continued efforts are needed to address the limitations of the map, particularly in terms of microzonation and data collection, to ensure effective disaster preparedness and resilience. Regular updates and integration with local-level risk assessments are crucial for maximizing the map’s utility in safeguarding lives and infrastructure.
Answer Length
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