‘Strike-slip’ movement of fault lines caused the disaster
THE CARIBBEAN is riddled with a complex network of tectonic fault lines resulting from the movement of the Caribbean plate, which is slipping eastwards at a rate of about 2cm a year, relative to the North American plate further to the north.
The boundary of these two tectonic plates lies off the north coast of Haiti, but there are several faultline systems to the south that cut across the country from east to west. It was the sudden “strike-slip” movement of one of these faultlines that led to the disaster.
Scientists calculate that the epicentre of the earthquake, which measured 7 on the Richter scale, was about 15km south-west of Haiti’s capital, Port-au-Prince. The point beneath the Earth’s surface where the rupture began – its hypocentre – was just 11km away, making it a relatively shallow shock.
“Closeness to the surface is a major factor contributing to the severity of ground shaking caused by an earthquake of any given magnitude,” said David Rothery, a planetary scientist at the Open University. “In this case, the epicentre was only 15km from the centre of Portau-Prince, which therefore suffered very heavily.”
Scientists said this week it was the largest earthquake to affect this area of the Caribbean for more than two centuries.
Haiti suffered a number of earthquakes in the 18th century: in 1701, 1751 and 1770. The 1751 earthquake, which was probably about 10 times bigger than the current one, destroyed the recently founded Portau-Prince.
Professor Roger Searle, an earth scientist at Durham University, said the earthquake released the energy equivalent of half a million tons of TNT but its impact would have been much greater than in developed countries because of poor building standards. – The Independent