Seismic Activity in the Nicobar Islands, India Region

The Nicobar Islands form part of the Andaman and Nicobar archipelago in the eastern Indian Ocean, situated along a tectonically active convergent margin. This region experiences frequent seismicity due to the ongoing subduction of the Indian Plate beneath the Burma Plate at the Sunda Trench. The islands rest on the overriding Burma Plate, where oblique convergence produces both thrust and strike-slip faulting. Historical records document major events, including the devastating magnitude 9.1–9.3 Sumatra-Andaman earthquake of 26 December 2004, which originated nearby and generated a transoceanic tsunami. Instrumental monitoring since 2000 has recorded two notable strong earthquakes in the immediate vicinity. On 24 July 2005, a magnitude 7.2 event occurred approximately 28 km from the reference location at a shallow depth. This quake reflected interplate thrusting typical of the subduction zone. Five years later, on 12 June 2010 at 19:26 UTC, a magnitude 7.5 earthquake struck directly at the reference site. The event originated at a focal depth of 35 km, consistent with rupture along the plate interface or within the downgoing slab. Both shocks occurred within the same segment of the trench, highlighting persistent strain accumulation and release along this portion of the margin. Geological studies indicate that the Nicobar Islands overlie a complex forearc system influenced by the collision of the Ninetyeast Ridge with the subduction zone. This interaction contributes to localized variations in seismicity and occasional volcanic activity on nearby islands. Updated assessments from regional seismic networks confirm that post-2010 activity has remained moderate, with no larger events recorded in the immediate area through the present. The 35 km depth of the 2010 mainshock placed it within the seismogenic zone capable of generating strong ground shaking across the islands, though the remote location limited widespread damage. Continued monitoring underscores the potential for future large earthquakes in this setting. The combination of rapid plate convergence rates exceeding 50 mm per year and the presence of locked patches along the megathrust supports long-term hazard evaluation for the Nicobar region. References: USGS Earthquake Catalog (events 2010-06-12 and 2005-07-24) Global CMT Project moment tensor solutions Indian Meteorological Department seismic bulletins