Environment Impact Study for Nicobar Project Downplays Earthquake Risks, Pg14

Context:

• The Environment Impact Assessment (EIA) for the ₹72,000-crore Great Nicobar Infrastructure Project (GNIP) has come under scrutiny for downplaying the region's earthquake and tsunami risks, despite warnings from geoscientists and previous studies highlighting seismic vulnerabilities.

Key Highlights

• EIA report claims low probability of a mega earthquake like the 2004 tsunami event.
• Relies on a 2019 IIT-Kanpur study, which mentions a return period of 420–750 years for magnitude 9+ earthquakes.
• Key uncertainty flagged by IIT-Kanpur study was not included in the EIA.
• Experts urge site-specific seismic assessments due to the region’s complex fault systems.
• Geologists warn of undocumented parallel rupture lines and non-linear recurrence patterns.
• GNIP includes a transshipment port, international airport, township, and 450 MVA power plant.
• Despite approvals, National Green Tribunal (NGT) has ordered a review due to ecological and tribal concerns.

Detailed Insights

• The Andaman-Sumatra subduction zone is geodynamically active, with a history of massive earthquakes and tsunamis.
• The 2004 tsunami was triggered by a 9.2 magnitude earthquake, the risk of which is considered “low” in the EIA despite historical precedent.
• The IIT-Kanpur study identified at least seven tsunami events in the past 8,000 years and noted a 2,000-year gap in sediment records, raising uncertainty.
• The study warned that the Nicobar segment still holds significant strain energy, making it vulnerable to future tsunamis.
• Scientists note that earthquake recurrence is not linear, and local fault ruptures or land-level changes can amplify risks.
• No site-specific seismic hazard study was commissioned for the GNIP, which increases the project’s vulnerability.
• Experts recommend avoiding large infrastructure projects in highly dynamic seismic zones like Great Nicobar Island.
• Government officials admit that decisions are made on calculated risks due to unpredictability but plan to include design safeguards.
• The region’s ecological sensitivity and presence of indigenous tribes add layers of social and environmental complexity to the project.

Scientific/Technical Concepts Involved

• Return Period: Estimated average time between events of a certain magnitude, used in seismic risk analysis.
• Tsunamigenic Earthquake: An undersea earthquake capable of generating a tsunami.
• Subduction Zone: A tectonic boundary where one plate moves under another, often causing major seismic activity.
• Seismic Hazard Assessment: Evaluation of the probability of occurrence of different levels of earthquake shaking at a site.