January 23, 2010

Aftershocks In Haiti Possible For Next 30 Days

A preliminary U.S. Geological Survey assessment has found that the sequence of aftershocks following the magnitude 7 earthquake that struck near Port-au-Prince, Haiti on Jan. 12 is likely to continue for months, possibly years.

The capital was hit by two fresh aftershocks on Friday, 10 days after the initial 7.0-magnitude quake killed at least 75,000 people and left half a million others homeless.

A team of USGS scientists predict that for the next 30 days there is a 3 percent chance of a magnitude 7 or greater quake, a 25 percent chance of a magnitude 6 or greater quake and a 90 percent chance of a magnitude 5 or greater quake.

"The frequency of events will diminish with time, but damaging earthquakes will remain a threat," the scientists warn.

The forecast is based on the aftershocks Haiti has already experienced and general statistics on aftershocks.

The scientists are also concerned because it's unclear how much of the Enriquillo-Plantain Garden fault, which bounds the North American and Caribbean plates, ruptured in the earthquake. Analysis of ground deformation at the surface using satellite and aerial photos and preliminary radar data suggests that the segment of the fault directly east of the rupture and directly under Port-au-Prince did not slip. This means it could rupture in the future.

At least four times in the past, earthquakes as big or bigger than the recent quake have struck Haiti. Two major quakes struck the capital city in 1751 and 1770. For this reason, the USGS cautions that as Port-au-Prince is rebuilt, future seismic risk must be taken into account.

Nearly 50 aftershocks have rocked Haiti since the initial earthquake, the strongest being a 5.9-magnitude tremor on Wednesday.


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