On Edge: The Great Nicobar project faces a great engineering question
Engineering assessments for the Great Nicobar Island Development Project are examining how to build major infrastructure — a transshipment port, greenfield airport, township, and power plant — on ground classified in Seismic Zone V, India's highest earthquake-risk category.
Great Nicobar's geology is marked by cyclical tectonic movement: slow uplift punctuated by sudden subsidence during major earthquakes, as seen when the island's southern tip dropped by several metres during the 2004 Sumatra-Andaman earthquake.
Proposed engineering responses include designing structures to Bureau of Indian Standards (BIS) and National Building Code earthquake-resistant specifications, dedicated tsunami shelters, and integration with existing early-warning and evacuation systems under the Andaman and Nicobar Islands Disaster Management Plan, 2016.
The discussion highlights a broader tension between the project's strategic and economic rationale and the engineering feasibility of permanent infrastructure on a seismically volatile landmass.
Seismic Zoning of India (BIS Seismic Zone Map)
India is classified into four seismic zones (II, III, IV, V) under the Bureau of Indian Standards code IS 1893, based on the maximum earthquake intensity a region has historically experienced or could experience. Zone V is the most seismically active, denoting areas that can experience earthquakes of intensity IX or higher on the MSK scale.
Key Details
- Zone V includes the Andaman and Nicobar Islands, Kashmir Valley, Himachal Pradesh, the Northeastern states, parts of Gujarat's Kutch region, and the Indo-Gangetic plain's northern fringe (near the Himalayan front).
- Zone classification determines mandatory earthquake-resistant design factors in building codes for that region.
- The Andaman-Nicobar arc lies along the boundary of the Indian and Burma microplates, part of the same subduction zone that produced the 2004 Sumatra-Andaman earthquake (magnitude 9.1-9.3), one of the largest recorded earthquakes.
Great Nicobar Island's Zone V status is the geological basis for the seismic-design debate — any structure built there under Indian law must meet the most stringent BIS earthquake-resistant construction standards applicable in the country.
Subduction Zones, Tsunamis, and the 2004 Sumatra-Andaman Earthquake
The Andaman-Nicobar Islands lie above a convergent plate boundary where the Indian/Australian Plate subducts beneath the Burma microplate — the same subduction system responsible for the December 2004 Sumatra-Andaman earthquake and the Indian Ocean tsunami that followed.
Key Details
- The 2004 earthquake (moment magnitude ~9.1-9.3) caused sections of Great Nicobar's southern coastline to subside by several metres within seconds, permanently altering the coastline.
- Historical seismic records for the region include the 1881 Nicobar Islands earthquake (magnitude ~7.9) and the 1861 and 2007 Sumatra earthquakes, indicating recurring mega-earthquake risk.
- Studies estimate a return period of roughly 420-750 years for mega-earthquakes (magnitude 9+) and 80-120 years for large earthquakes (magnitude >7.5) in this subduction zone.
- A subduction zone differs from a strike-slip or transform boundary (e.g., along the Himalayan front, which is a collision zone) — subduction zones generate both intense shaking and tsunami risk due to vertical seafloor displacement.
The project's central engineering problem — designing permanent, heavy infrastructure like a deep-water port and airport runway on ground proven to subside abruptly — stems directly from this subduction-zone geology, distinguishing Great Nicobar's risk profile from purely shaking-based seismic risk elsewhere in India.
Coastal Regulation and Environmental Clearance Framework (ICRZ/CRZ)
Large coastal infrastructure projects in India require clearance under the Environment Impact Assessment (EIA) Notification, 2006, and the Island Coastal Regulation Zone (ICRZ) Notification, 2019 (the island-specific counterpart to the mainland Coastal Regulation Zone Notification, 2011/2019).
Key Details
- The Great Nicobar project received clearance involving 42 compliance conditions, including provisions for compensatory afforestation and forest-cover diversion limits.
- ICRZ 2019 classifies island coastal areas into zones (analogous to CRZ-I to CRZ-IV on the mainland) governing permissible construction distances from the high-tide line.
- Disaster management planning for the project falls under the Andaman and Nicobar Islands Disaster Management Plan, 2016, framed under the Disaster Management Act, 2005.
Even where environmental and coastal clearances have been granted, the underlying seismic engineering question — whether structures can be safely engineered against sudden multi-metre subsidence — remains a live technical debate independent of the regulatory clearance process.
- Andaman & Nicobar Islands: classified in Seismic Zone V (highest risk category under BIS IS 1893).
- 2004 Sumatra-Andaman earthquake: magnitude ~9.1-9.3; caused several-metre subsidence at Great Nicobar's southern tip.
- Estimated return period: mega-earthquakes (M9+) every 420-750 years; large earthquakes (M>7.5) every 80-120 years.
- Great Nicobar project scale: proposed over roughly 166 sq km (about part of the island's total ~910 sq km area), including an International Container Transshipment Terminal at Galathea Bay, a greenfield airport, a township, and a power plant.
- Governing framework: EIA Notification 2006, ICRZ Notification 2019, Andaman and Nicobar Islands Disaster Management Plan 2016.