The Caribbean is riddled with a complex network of tectonic fault lines resulting from the movement of the Caribbean plate.
It is slipping eastwards at a rate of about 2cm a year, relative to the vast North American plate to the north.
The boundary of these two tectonic plates lies off the north coast of Haiti, but there are several fault-line systems to the south that cut across the country from east to west.
It was the sudden strike-slip movement of one of these fault lines -- the Enriquillo-Plantain Garden fault zone -- that led to the disaster.
Scientists calculate that the epicentre of the earthquake, which measured seven on the Richter scale, was approximately nine miles south-west of Haiti's capital, Port-au-Prince.
The point beneath the Earth's surface where the rupture began -- its hypocentre -- was just six miles away, making it a relatively shallow shock.
"Closeness to the surface is a major factor contributing to the severity of ground shaking" said planetary scientist David Rothery.
Experts warned that earthquakes of this size always have aftershocks that can last for many weeks.