Seismic Activity and Geological Context of the Nicobar Islands Region

The Nicobar Islands form part of India's Andaman and Nicobar archipelago, situated along a tectonically active boundary where the Indian Plate subducts beneath the Burma Plate. This subduction zone drives frequent seismic events, with the islands positioned near the trench axis. The regional geology features a mix of volcanic arcs, accretionary wedges, and sedimentary basins shaped by ongoing convergence at rates of approximately 5–6 cm per year. A magnitude 7.2 earthquake struck the Nicobar Islands region on 24 July 2005 at 15:42 UTC, with a focal depth of 16 km. The event occurred within a zone of elevated seismicity that has produced multiple strong shocks since 2000. Another magnitude 7.5 earthquake took place on 12 June 2010, located 28 km from the 2005 epicenter. These events highlight the persistent strain accumulation and release along the plate interface. Historical records indicate that the Nicobar Islands have experienced significant earthquakes tied to the same subduction dynamics. The 2004 Sumatra–Andaman earthquake, though centered farther south, triggered widespread aftershocks throughout the Nicobar segment. Post-2004 observations show accelerated slip and increased background seismicity in the region, consistent with viscoelastic relaxation and afterslip processes. Geological mapping reveals that the islands rest on a complex assemblage of ophiolitic rocks, Eocene to Miocene limestones, and Quaternary coral reefs uplifted by repeated coseismic deformation. Paleoseismic studies document prehistoric megathrust ruptures, underscoring a long-term cycle of great earthquakes interspersed with moderate-to-large events such as those recorded in 2005 and 2010. Current monitoring by regional seismic networks continues to track microseismicity and deformation, providing data essential for refining hazard assessments. The combination of shallow focal depths and proximity to populated islands elevates the potential for strong ground shaking and associated hazards such as landslides and tsunamis.

References

USGS Earthquake Catalog (events 2005-07-24 and 2010-06-12)
India Meteorological Department Seismic Bulletins
Geological Survey of India, Andaman-Nicobar Tectonic Reports