Crustal Deformation and Seismic History Associated with the 2004 Indian Ocean Earthquake: A Perspective from the Andaman-Nicobar Islands

Abstract

The Indian Ocean earthquake of 26 December 2004 led to significant ground deformation in the Andaman and Nicobar region, accounting for ϳ800 km of the rupture. Part of this article deals with coseismic changes along these islands, observable from coastal morphology, biological indicators, and Global Positioning System (GPS) data. Our studies indicate that the islands south of 10Њ N latitude coseismically subsided by 1-1.5 m, both on their eastern and western margins, whereas those to the north showed a mixed response. The western margin of the Middle Andaman emerged by Ͼ1 m, and the eastern margin submerged by the same amount. In the North Andaman, both western and eastern margins emerged by Ͼ1 m. We also assess the pattern of long-term deformation (uplift/subsidence) and attempt to reconstruct earthquake/tsunami history, with the available data. Geological evidence for past submergence includes dead mangrove vegetation dating to 740 ‫ע‬ 100 yr B.P., near Port Blair and peat layers at 2-4 m and 10-15 m depths observed in core samples from nearby locations. Preliminary paleoseismological/tsunami evidence from the Andaman and Nicobar region and from the east coast of India, suggest at least one predecessor for the 2004 earthquake 900-1000 years ago. The history of earthquakes, although incomplete at this stage, seems to imply that the 2004-type earthquakes are infrequent and follow variable intervals.

Geohazards and myths: ancient memories of rapid coastal change in the Asia-Pacific region and their value to future adaptation

“…Survivors of all these events are known in the myths, so it is likely that some inhabitants of the affected islands had enough time to escape, suggesting that coseismic subsidence may have been followed by slower aseismic subsidence before the entire island became submerged. Although it is impossible to calculate the contributions of coseismic and aseismic subsidence to the particular instances of island disappearance, it is likely that the latter was greater, given that maximum magnitudes of observed coseismic subsidence in most such geotectonic situations are only around 1 m [73,74].…”

Introduction to the Special Issue on the 2004 Sumatra–Andaman Earthquake and the Indian Ocean Tsunami

“…The preliminary paleoseismic and paleotsunami work of Rajendran et al (2007) suggests otherwise. They report preliminary results from a variety of promising paleoseismic and paleotsunami sites on the Andaman islands and on the coast of India that suggest such events are, in fact, quite rare; sand layers intercalated with archeological ruins on the Indian coast imply that the previous devastating tsunami there may have occurred about a thousand years ago.…”

“…In addition, the model of postseismic deformation suggests that slip continued on the interface beyond the 500-sec seismic slip, with ϳ2.5 ‫ן‬ 10 22 N m of postseismic geodetic moment release. Rajendran et al (2007) provide the most comprehensive evidence to date from the field for uplift and subsidence on the Nicobar and Andaman islands. They use mangrove forests, corals, and anthropogenic features to document subsidence at all visited locations on the Nicobar islands and a complex pattern of subsidence and emergence on the coasts of the Andaman islands.…”

Geoarchaeological evidence of a Chola‐period tsunami from an ancient port at Kaveripattinam on the southeastern coast of India

“…The former is known to have generated a few large earthquakes during recent and historic times. Among the earlier earthquakes, only those in 1881 (M w 7.9) and 1941 (M w 7.7) are significant (Bilham et al, 2005;Rajendran et al, 2007). The 1881 earthquake caused a tsunami surge that reports say did not exceed 0.75 cm at Car Nicobar (Rogers, 1883; Table I).…”