Haiti quake was caused by previously unknown fault

By Victoria Gill
Science reporter, BBC News

Image caption,
The cause of the quake was more complex than first thought

This year's devastating earthquake in Haiti was caused by a previously unknown fault, according to scientists.

This discovery, the researchers say, could be the first sign of a larger system of seismic faults in the area.

The Enriquillo fault, which runs through Port au Prince, was originally blamed. But new evidence has shown that it was not linked to the event.

Eric Calais from Purdue University in Indiana, presented the findings at an scientific meeting in Brazil.

At the American Geophysical Union's Meeting of the Americas in Foz do Iguacu, he explained that the earthquake was more complicated than previously thought.

He said that the first "give-away" was the fact that there was no surface break along the known Enriquillo fault. This led to a search for other faults or fractures in the Earth's crust, which may have slipped and caused the event.

The earthquake in January 2010 killed more than 200,000 people and left 1.5 million homeless. Amid the devastation, it took scientists several months to gather data about what really shifted the ground.

Using techniques including GPS and radar, Dr Calais and his colleagues were able to show that the "pattern of motion was incompatible with slippage on a vertical fault such as the Enriquillo".

Further calculations showed that the only way to fit the observations was by mapping the slip to a fault that was slightly oblique to the Enriquillo and dipped 60 degrees to the north.

This previously unmapped fault was only brought to scientists' attention by the earthquake itself - it may be one part of a larger system of seismic faults.

Dr Calais told BBC News that searching for and studying this system was crucial in order to define "the long-term hazard level in Haiti".

"Fault slippage during an earthquake alters the hazard level in the region in a way that depends on the fault location, geometry, and slippage," he said.

"In some areas hazard will be slightly increased, in others it will be decreased. There is ongoing research on what the specific consequences might be for southern Haiti."

Image caption,
The quake was originally "blamed" on the Enriquillo fault

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