TRI-STATE -- An aftershock could follow the 3.6-magnitude earthquake that struck the Washington, D.C., area Friday morning, but the strength likely would be weaker than the original, according to a federal official.
Paul Caruso, a geophysicist with the U.S. Geological Survey, said the magnitude of aftershocks typically averages about one point less than the earthquake.
The mid-Atlantic doesn't get hit with large earthquakes because it's too far away from major fault lines, Caruso said. The nearest major fault line is about 1,500 miles away in the middle of the Atlantic Ocean.
"We can still have earthquakes, but we don't see large ones," Caruso said.
The solid rock structure along the East Coast also helps to minimize the severity of earthquakes, he said.
Caruso said earthquakes typically don't cause damages and casualties unless the magnitude reaches at least 5.5.
Thursday's quake hit at 5:04 a.m. with a magnitude of 3.6, The Associated Press reported. The quake was centered near Rockville, Md., according to Randy Baldwin, a physicist with U.S. Geological Survey's National Earthquake Information Center.