Sumatra – Andaman Earthquake and Tsunami 26 December 2004

The Sumatra-Andaman subduction zone has been a known potential tectonic candidate for earthquakes. Tsunamis are rate but not totally absent. Yet there was insufficient knowledge on its capability for developing such an incomprehensible tsunami. The impression that tsunami is largely a Pacific Ocean phenomenon has been drastically confuted by the Indian Ocean earthquake and tsunami of 26 December 2004. This was one of the largest interpolate shallow-thrust earthquakes that occurred at the interface of the subducting Indian lithosphere and the overriding Burma plate. The event happened to be the second largest earthquake in the recorded history after the Chile Earthquake of 1960 (Mw 9.5). The mainstock of the great earthquake of 26 December measured Ms 8.6 (IMD), MS 8.8 (GSI, Nagpur), Ms 8.6 (GSI, Jabalpur), Mw 9.0 (USGS), (revised MW 9.3) and occurred off the west coast of northern Sumatra (Indonesia) at 00:58:53 hrs (UTC). [06:28:51.1hrs IST (IMD)]. This undersea earthquake triggered giant tsunamis that devastated the coastal regions of the countries rimming the Indian Ocean traveling as far as the coast of east Africa. In India, damage from the tremor of the earthquake itself was moderate to high in the Anadman and Nicobar Islands. Above and beyond, the high tsunami waves unleashed by the earthquake wreaked havoc on life and property in the coastal regions of Andhra Pradesh, Tamil Nadu, Kerala and Andaman & Nicobar island. Besides death of 10,479 people, a total of 2,39,024 dwelling units were affected, 35,605 cattle lost, 22,750 hectares of cropped area and 83,788 boats damaged in the calamity in India alone. This estimate may change with time but the frightening memory and potential threat will haunt the nation and the earthscientists in particular for years to come. GSI made a conscientious attempt to study and analyze the event for immediate planning and for posterity. The collation of data on earthquake and tsunami survey of one of the largest recorded seismic event is indeed an assignment for the sake of better understanding of a lesser-known phenomenon in this part of the world. The attempt will be rewarding if new frontiers of science open up for the safety and existence of all living milieu in this fragile tectonic regime.