That boom you felt or heard Friday night was an earthquake, according to the U.S. Geological Survey.

Philadelphia and Bensalem police received numerous calls around 10 p.m. reporting an explosion on Knights Road near the Franklin Mills Mall, but no evidence of an explosion was found.

PECO and PGW crews also found no signs of an explosion.

But the USGS has confirmed that an earthquake with magnitude 1.7 took place on Chalfont Drive near Academy Road at 9:33 p.m. The quake occurred at a depth of 2.6 miles.

The USGS website said the urban corridor (New York-Philadelphia-Wilmington) is laced with known faults but numerous smaller or deeply buried faults remain undetected.

It is difficult to determine if a fault is still active and could slip and cause an earthquake, according to the USGS.

Moderately damaging earthquakes strike somewhere in the urban corridor roughly twice a century, and smaller earthquakes are felt roughly every 2-3 years.