FROM THE human point of view, a magnitude 7.0 earthquake could hardly have struck in a worse place: close to the surface, beneath a poor and densely populated country where buildings are not designed to withstand severe tremors.
While industrialised and earthquake- prone countries have construction codes to protect vulnerable buildings – for example, by incorporating mechanical damping systems – Haiti has neither the funds nor the expertise to do so. Though it has not been hit by such a strong quake since the 19th century, the northern Caribbean is an active seismic zone.
“The island of Hispaniola, which is shared by Haiti and the Dominican Republic, lies between the North American and Caribbean tectonic plates, which are shearing, crushing, grinding the island,” said Mike Blanpeid of the US Geological Survey. “As that happens, earthquakes pop off.”
Tuesday’s was caused by a slip in the Enriquillo-Plantain Garden fault, which marks the boundary between the two plates. “This fault has been locked for the past 250 years, gradually accumulating stress which has now been released in a single large earthquake,” said Roger Musson of the British Geological Survey. The energy released was equivalent to a half-megaton nuclear bomb.
The US Geological Survey says there were 17 earthquakes of magnitude 7.0 or greater during 2009. But few have such terrible consequences. “The earthquake that struck Haiti was so devastating because . . . its source was at a shallow depth of about 10km,” said David Rothery, planetary scientist at Britain’s Open University.
“Closeness to the surface is a major factor contributing to the severity of ground-shaking caused by an earthquake of any given magnitude. Furthermore, shaking tends to be greatest directly above the source,” Dr Rothery added.
“In this case the epicentre was only 15km from the centre of Port-au-Prince, which therefore suffered very heavily.”
Experts fear the worst is still to come. There will be aftershocks for weeks and, said David Kerridge, head of earth hazards at the British Geological Survey, “there is a strong possibility of landslides”.
“Due to disruptions in communications, the full extent of the disaster might not be clear for a few days,” he said.
David Gordon, of the Townsend Centre for International Poverty Research, said half of all Haitian children were living in squalid and unsafe conditions. “It is this kind of poorly built housing that suffers great damage in earthquakes and results in many poor adults and children being killed or injured.” – (Copyright The Financial Times Limited 2010)