By Mohammed Shafeeq| IANS| December 26, 2014| 8.00 pm ISTThe energy released by the Indian Ocean tsunami of 2004 equalled 40,000 Hiroshima-sized atomic bombs, according to eminent earth scientist Harsh Gupta.The massive undersea earthquake measuring 9.1 on Richter Scale, which triggered the worst-ever tsunami, caused 1,500 km long, 300 km wide and 20 meter vertical rupture.He revealed this while addressing a national workshop organised by the Indian Tsunami Early Warning Centre (ITEWC) here to mark the 10th anniversary of the disaster.The tsunami claimed 2.38 lakh lives in 14 countries. As many as 10,749 people were killed in India and 5,640 went missing. More than 1.5 million people were displaced in the affected countries. Gupta, former secretary of ministry of earth sciences, said it was a rare event which occurs once or twice a century.The experts at the workshop recalled that the disaster was a rude shock as most people had not even heard of tsunami."We all watched on TV how the tragic events unfolded that Sunday," said another former secretary. P.S. Goel. They said everyone including institutes which monitor earthquakes were caught off guard.Gupta, who later played a key role in developing the tsunami early warning system, recalled the efforts taken in the aftermath of the horror.He pointed out that not every earthquake triggers tsunami. "Whenever an earthquake occurs through the ocean bottom and the rupture occurs in the sea bed creating a vertical displacement of the ocean bed and the entire column of water above gets displaced; this column gets oscillate and moves out and it is called tsunami wave," he said.Gupta, an authority in seismology, said unlike the Pacific Ocean which is covered with geological features capable of generating tsunamis, there were just two such zones in the Indian Ocean One of them was the Andaman-Nicobar-Sumatra island arc. The scientist said the world had seen three great tsunamis: in 1755, 2004 and 2011.The first major tsunami occurred on Nov 1, 1755, caused by the Lisbon earthquake. The most damaging tsunami ever in the Atlantic ocean claimed 90,000 lives. As no major tsunami occurred till 2004, there was no awareness among people.He pointed out that those walking on the beach in Chennai on the morning of Dec 26, 2004 rushed to pick up pebbles and shells when water receded in the ocean. In no time high waves lashed the coast, washing them away.Gupta said the destruction was massive as the rule which prohibits any commercial activity in the 500 meter area along the coast was flouted.He pointed out that 2011 earthquake and the resultant tsunami in Japan were a surprise to the seismologists around the world as the height of the tsunami far exceeded the estimated heights. The disaster claimed about 20,000 human lives and also caused nuclear accidents.IANS