SAN JUAN, Puerto Rico _ Puerto Rico is slightly more likely to be hit with an earthquake of magnitude 6.0 or higher over the next week, the U.S. Geological Survey said, after an intense aftershock Saturday led the agency to tweak its statistical models.
In an "Aftershock Forecast" updated Sunday, the USGS said the chance of a magnitude 6.0 earthquake or higher was 11% _ up from 7% a week ago. However, the chance of a magnitude 7.0 earthquake remained at just 1%.
"Such an earthquake is possible but with low probability," the USGS said.
Puerto Rico's southern coast has been rattled by a series of quakes since Dec. 28 and was hit by the "mainshock," a magnitude 6.4, on Tuesday. Since then aftershocks, most of them barely perceptible, have been part of daily life on the island. On Saturday, however, a 5.9 magnitude quake caused fresh damage and renewed panic.
"No one can predict the exact time or place of an earthquake, including aftershocks," the USGS cautioned. "Our forecast changes as time passes due to decline in frequency of aftershocks, larger aftershocks that may trigger further earthquakes, and changes in forecast modeling based on data collected for this earthquake sequence."
The USGS also produces 30-day "scenarios," that also suggest that a larger earthquake is unlikely. That month-long prediction remains unchanged.
The government estimates that the earthquakes have damaged more than 559 structures and caused $110 million in damage. On Saturday, Gov. Wanda Vazquez signed a major disaster declaration and said she was sending $12 million dollars to hard-hit municipalities. That will allow them to start the recovery process ahead of federal funds that the island is expecting.
Puerto Rico _ a U.S. territory _ is squeezed between the North America and Caribbean tectonic plates and low-level seismic activity is common. But the island's southern coast (where the North America plate slips beneath Puerto Rico at an area known as Muertos Trough) began to reactivate shortly after Christmas.
On Dec. 28, the USGS recorded two quakes of magnitude 4.7 and 5.0. Since then more than 400 earthquakes have occurred in the region, 11 of which were greater than magnitude 4.0.
"The proximity of these events to Puerto Rico, and their shallow depth, mean that dozens of these events have likely been felt on land," the USGS said.
