Why the 6.7 magnitude earthquake in Andaman and Nicobar did not trigger a tsunami

India Today

6 days ago

A 6.7-magnitude earthquake shook the Andaman and Nicobar Islands on Monday night, raising concerns of a large tsunami. However, no such warning was issued.It was triggered by intricate and powerful geological processes deep beneath the seafloor. This region is globally recognised for seismic activity because it lies atop a major tectonic boundary, where the Indian Plate is gradually moving northeast and subducting under the Burma (or Sunda) Microplate.advertisement
This convergence is neither simple nor direct: the Indian Plate's movement occurs at an angle (called oblique subduction), introducing both compressive and shearing forces along the subduction zone.EQ of M: 6.7, On: 29/07/2025 03:40:32 IST, Lat: 57.90 S, Long: 157.88 E, Depth: 10 Km, Location: Macquarie Island Region.For more information Download the BhooKamp App https://t.co/5gCOtjcVGs @DrJitendraSingh @OfficeOfDrJS @Ravi_MoES @Dr_Mishra1966 @ndmaindia pic.twitter.com/TpTyrf6wGx— National Center for Seismology (@NCS_Earthquake) July 28, 2025WHAT HAPPENED BELOW THE SURFACE?The earthquake's epicenter was relatively shallow, about 10km beneath the Earth's surface. Such shallow quakes, especially in subduction zones like this one, often result in vigorous shaking at the surface.The tectonic landscape here is anything but simple; it's a broad zone marked by numerous fault types, including thrust faults where one plate pushes beneath another, and major strike-slip faults where plates slide past each other horizontally.Oblique subduction dominates the area as the Indian Plate becomes squeezed and sheared as it slides both under and past the Burma Plate. This produces immense stress not only at the primary subduction interface but also along sliver faults, large strike-slip systems running parallel to the plate boundary.In the Andaman-Nicobar region, many sizable earthquakes are directly linked to left-lateral strike-slip movement. When tectonic stress builds up enough to overcome friction along these faults, the rock suddenly shifts, causing an earthquake.FAULT NETWORKS AND RUPTURE DYNAMICSThe Andaman and Nicobar region is crisscrossed by a complex network of faults, including large systems like the Andaman-Nicobar Fault. These accommodate both lateral (sideways) and vertical crustal movements caused by the interplay between the Indian and Burmese plates.Sometimes, this leads to not just single earthquakes but clusters or swarms, as multiple segments rupture or adjust in rapid succession.WHY NO TSUNAMI THIS TIME?Despite its strength, this earthquake didn't generate a significant tsunami.That's because the principal movement was horizontal, which displaces less water than vertical motion.In contrast, the catastrophic 2004 Indian Ocean earthquake involved much greater vertical movement along a 'megathrust' fault, leading to massive seabed displacement and a devastating tsunami.The lack of major damage can be attributed to the earthquake's remote epicentre, sparse population, primarily horizontal fault movement, and increased regional preparedness and resilient infrastructure since past disasters.advertisementThe outcome highlights the importance of both natural factors and human adaptation in reducing earthquake risks in seismically active but isolated regions- Ends