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.

Though the frequency of aftershocks will decrease over time, there is still potential for quakes large enough to cause more damage in the coming months, and a small possibility of an event larger than the main shock, according to a team of USGS scientists.

Their initial probability estimates for the next 30 days are that 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.

"Any aftershock above magnitude 5.0 will be widely felt and has the potential to cause additional damage, particularly to vulnerable, already damaged structures," according to the USGS statement released Thursday evening.

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

Haiti experienced a magnitude 5.9 aftershock on Wednesday. The USGS expects two or three more of at least magnitude 5 in the nest 30 days.

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.

USGS webpage for the January 12 Haiti earthquake and aftershocks

Images: 1) NASA/USGS. 2) NASA

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