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The preliminary reports suggested that the earthquake that devastated Haiti occurred at the Enriquillo fault that runs right through Haiti and is situated along the boundary between the Caribbean and North American plates. This was based on preliminary observations and previous studies suggesting this fault was primed for a rupture.

The research team found, however, that some of the faults in the area where moving in unexpected directions. The Enriquillo fault is what's known as a vertical fault, but the new data suggests that the earthquake did not happen on a vertical fault, Calais said.

"Most of the slip, if not all, was on the unmapped fault, not the Enriquillo," Calais said.

The Enriquillo-Plantain Garden fault system (EPGFZ) has not produced a major earthquake in recent decades. The EPGFZ is the likely source of historical large earthquakes in 1860, 1770 and 1751, though none of these has been confirmed in the field as associated with this fault.

• Haiti quake caused by previously unknown fault