The earthquake that devastated Haiti's capital and killed as many as 300,000 people in January may have been caused by an unseen fault and pressure could be building for another quake, seismic experts said on Sunday.
Two papers, published in the journal Nature Geoscience, take different approaches but both conclude the fault originally blamed for the quake was not the real source, and that it remains a threat.
"As the Enriquillo-Plantain Garden fault did not release any significant accumulated elastic strain, it remains a significant seismic threat for Haiti and for Port-au-Prince in particular," Eric Calais of Purdue University in Indiana and colleagues wrote.
"Much work remains to be done to identify and quantify potential earthquake sources in and around Hispaniola, an island where vulnerability to earthquake shaking will probably remain high in the near future," they said.
Haitians are still digging out after the magnitude 7 quake that shattered large parts of Port-au-Prince on January 12, making more than 1 million people homeless. Now cholera has broken out amid the devastation.
Calais' team said an analysis of slight shifts of ground motion picked up by global positioning system and radar devices suggest an as-yet undescribed fault near the town of Leogan may have been the source of the January quake.
At first, scientists focused on the Enriquillo-Plantain Garden fault on Haiti's southern peninsula -- one of two main faults in the region.
But the team said measurements of ground motion suggest the movement caused the surface to bulge, but not to rupture. Calais' measurements led them to conclude a previously unknown fault must have caused the January quake.
A separate study led by Carol Prentice of the U.S. Geological Survey in Menlo Park, California, also said the 2010 quake may not have relieved any pressure on the Enriquillo-Plantain Garden fault system.
Prentice's team used remote sensors and field studies to map changes in the land surface caused by the January quake or an earlier event.
They found nine streams whose beds had been offset by one of two large earthquakes that occurred on the Enriquillo-Plantain Garden fault system in 1751 and 1770. But the 2010 quake did not leave a surface trace and Prentice worries that may mean the strain accumulated since the earlier large quakes was not released.
"The lack of surface rupture is unusual," Prentice's team wrote.
"The Enriquillo-Plantain Garden fault zone remains a serious seismic hazard for Haiti, particularly for the Port-au-Prince area."
Calais was part of a group of experts who warned Haitian officials in 2008 that there could be a 7.2 magnitude quake on the horizon and he said in February the island was risk for another big temblor.