A moderate earthquake, strongest since 1999, hit Southern California, swaying buildings and rattling nerves but doing little damage.
The tremor measured 5.4 on the Richter scale and was followed by some 50 after shocks - the strongest with a magnitude of 3.2.
People ran out of buildings as the tremor shook the area just before lunch time on tuesday and several schools and offices were temporarily evacuated.
Inspection teams were immediately dispatched to check for possible structural damage to bridges and other structure but found only one water main break.
However, cell phone lines were jammed as people tried to contact their loved ones and at one stage officials asked people to reduce the usage.
The epicenter was about 45 km from the second largest city of Los Angeles and was felt as far away as Las Vegas.
Patrons at the Disneyland resort were taken off the rides which were inspected for any damage. But reports said there was no damage.
Many residents experienced an eerie, dizzying sensation of having rolled from side to side on rollers that are common in high-rise buildings retrofitted to withstand earthquakes, which leave buildings swaying for several seconds after a quake, the New York Times said.
The US Geological Survey said the quake was shallow, about 13km deep.