The tsunami was triggered by one of the most powerful (9.3 on the Richter scale) and longest (almost 10 minutes) earthquakes ever recorded, with a force 1,500 times the atom bomb at Hiroshima. Its epicentre was off the west coast of Sumatra and the rupture along a tectonic plate subduction zone was 600 miles (966 km) long, raising the sea-floor several yards and shifting it horizontally around 33 ft. (10 m). This displaced massive volumes of seawater. The resultant tsunami first struck the neighbouring coast of Aceh in Sumatra, attaining heights of 98 ft (30 m), and the greatest number of casualties occurred here. An hour later it reached the coasts of Thailand, followed just 30 minutes later by eastern India and Sri Lanka. In each case, the populations were taken by surprise, as no warning systems were in place. The tsunami still had sufficient power to cause destruction and casualties on the opposite side of the Indian Ocean when it hit the east African coast 4,400 miles (7,082 km) some seven hours after the earthquake. The total death toll has been estimated at c. 230,000, possibly the worst natural disaster of the industrial era.
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