"Low" number of Va. earthquake aftershocks felt

RICHMOND, Va. - The 5.8-magnitude earthquake Tuesday that shook people from Georgia to Canada has produced at least four aftershocks and more are likely to occur.

The U.S. Geological Survey said the aftershocks around the central Virginia epicenter ranged in magnitude from 4.2 to as little as 2.2 since the strongest earthquake to strike the East Coast since World War II.

There's a chance there were even more aftershocks, but the USGS hasn't received more detailed data from a network it relies on for larger number of local seismographs that record ground movements caused by earthquakes.

"For the size earthquake that occurred, I think the number of aftershocks so far has been remarkably low," said Amy Vaughan, a geophysicist with the USGS Earthquake Information Center in Colorado. "I don't know if that's an indication of things to come or not. ... There's likely there will be some more, but I don't know for how long and how large."

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Aftershocks could be expected "for days, if not weeks," Vaughan said. "A size like this probably wouldn't go into months, but it very well could."

Experts have earlier said that aftershocks were likely in the coming days. Seismologist Jim Gaherty, Lamont research professor at Columbia University, told CBS News: "Generally the aftershocks will be smaller than the main shock and they'll over time become less frequent and they'll become ... smaller and smaller, so every day the risk of a large aftershock goes down."

Typically, the larger the quake, the longer and the greater extent of aftershocks. Shallow earthquakes like the one in Virginia also tend to generate numerous aftershocks, said Don Blakeman, another geophysicist at the Earthquake Information Center. But it's rare to have an aftershock of comparable size to the initial event.

It's also possible that people closest to the epicenter could feel much smaller aftershocks that the agency wouldn't necessarily be able to confirm immediately, aftershocks that don't register at all, or ones that people just think are happening, Blakeman said.

"When these things occur, we have a certain number of people who are going to be a little jumpy and they start feeling things," he said.

In the epicenter of the earthquake in Mineral, Va., CBS News reported an aftershock Tuesday night in the parking lot of supermarket Miller's Market while working on a story. As of Wednesday morning, kids from the area will not report to class until after Labor Day because of damage to school buildings