In California, an small earthquake quickly gets people wondering whether it was a precursor to "The Big One."
But experts say there's little chance Friday morning's 3.6-magnitude temblor centered in Rockville was a foreshock to a larger shaker -- although it was followed quickly by a 2.0-magnitude aftershock.
"Most likely this is all we're going to see," said John Bellini, a geophysicist with the U.S. Geological Survey.
Quake safetyD.C.-area residents rarely have to think about what to do during an earthquake. Here are a few tips — just in case.If you are indoors » Take cover under a desk or table. Plan B should be an inside wall or doorway.» Stay away from windows and outside walls, anything that could shatter or fall on you.» If you’re sleeping, stay in bed and cover your head with a pillow.» Stay inside until the shaking stops.If you are outdoors » Stay outside and move away from buildings and streetlights.If you are in a vehicle » Stop quickly and stay in the vehicle. Avoid stopping near trees, buildings or overpasses.» Proceed cautiously after the earthquake has ended. Watch for road and bridge damage.Information from D.C. Emergency Management Agency
Maryland is considered small potatoes for seismologists.
"The eastern U.S. is not considered to be seismically active at all," Bellini said.
Even so, numerous fault lines crisscross the region, and when they build up enough tension, the earth under the Washington area feels it.
And unlike disturbances in California, scientists say they can't pin down which faults cause which earthquakes in Maryland, nor can they for most of the land east of the Rocky Mountains. That's because eastern faults are too deeply buried and have too few earthquakes for scientists to pin down their exact locations.
But scientists say that's not a cause for concern.
"What does it matter which fault it's on? [Knowing so] makes us feel better because we feel like we have some control over it. But it doesn't really matter," said Lucy Jones, a seismology expert from the California Institute of Technology.
Scientists say earthquakes in Maryland are rare, but not unprecedented.
"Every three or four years, there is some very small earthquake happening," said University of Maryland geology professor Laurent Montesi.
Before Friday's 5:04 a.m. wake-up call, the last time Washington area had felt an earthquake was Dec. 9, 2003, when a 4.3-magnitude quake struck west of Richmond.
Since 1980, 14 earthquakes have been felt within 50 miles of Friday's quake in Rockville, according to U.S. Geological Survey data.