October 25, 2010

More Earthquakes For Haiti?

The deadly Haiti earthquake that killed upwards of 300,000 people in January may have been caused by a previously unknown fault and pressure could be building for another seismic catastrophe, Reuters reported on Sunday.

Two reports were published in the journal Nature Geoscience that follow different paths but ultimately conclude the fault that was originally blamed for the earthquake was not the real source, and it is still a real 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.

The Caribbean country is still feeling the aftereffects of the magnitude 7.0 quake that destroyed large areas of Port-au-Prince on January 12, causing more than 1 million people to become homeless. And now, to make matters worse, the country is also dealing with an outbreak of cholera.

Calais' team said they found slight shifts of ground motion picked up by GPS and radar devices that suggest an undescribed fault near the town of Leogan may have been the actual source of the devastating January quake.

Scientists were first focused on the Enriquillo-Plantain Garden fault on Haiti's southern peninsula.

The team, however, said measurements of ground motion suggest the movement caused the surface to bulge, but not to rupture. The measurements led the team to conclude a previously unknown fault must have caused the quake.

Another study, led by Carol Prentice of the US Geological Survey (USGS) in Menlo Park, California, has also suggested the quake may have not released any pressure on the Enriquillo-Plantain Garden fault system.

Prentice and his team used remote sensors and field studies to map changes in the land surface caused by the earthquake, or perhaps an earlier event. They found nine streams whose beds had been offset by one of two massive quakes that occurred on the Enriquillo-Plantain Garden fault system in 1751 and 1770. But the 2010 seismic event did not leave a surface trace and Prentice is concerned that may mean the strain built up since the earlier quakes was not released.

"The lack of surface rupture is unusual," Prentice and colleagues wrote. "The Enriquillo-Plantain Garden fault zone remains a serious seismic hazard for Haiti, particularly for the Port-au-Prince area," they added.

A group of experts had warned Haiti officials in 2008 that the country could be at risk of a 7.2 magnitude quake in the near future, and Calais, who was among that group, said in February the island was at risk for another big one.


Image Caption: Damaged buildings in Port-au-Prince. Credit: Marco Dormino/United Nations Development Program/Wikipedia


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