Very minor earthquake causes boom heard in Philly

The U.S. Geological Survey says a very minor earthquake caused a mysterious boom heard in Northeast Philadelphia.

USGS geophysicist John Bellini says Friday night's earthquake was centered near Cornwells Heights and Eddington, Pa., just northeast of Philadelphia and west-northwest of Beverly, N.J.

Bellini says the magnitude-1.7 quake was so small it was unable to do any damage. He says to residents it might have sounded like "a big truck going by."

Earthquakes are fairly common but usually are so small people don't feel them. A quake generally would have to be at least magnitude 2 or 3 to be felt. A quake of magnitude 4 can cause moderate damage.

The U.S. Geological Survey said Saturday it had no reports of anyone feeling Friday's quake. But local police and firefighters say some residents felt their houses shake.