A magnitude 5.3 earthquake has struck under the ocean off Southern California and was felt widely along the mainland coast.
There were no immediate reports of damage on Thursday except to a chimney on one of the Channel Islands.
The US Geological Survey said the quake occurred at 12:29pm in the Channel Islands region, about 38 miles southwest of the California city of Ventura.
Some bricks fell from a chimney at an 1860s ranch on Santa Cruz Island but no one was hurt, Yvonne Menard said, spokeswoman for Channel Islands National Park.
The quake's epicentre was 17 miles from Santa Cruz Island, which is largely unpopulated but does have some staff and is visited by campers.
Authorities in Los Angeles and Ventura counties did not report any immediate damage.
The Los Angeles Fire Department said it went into "earthquake mode" and firefighters from all 106 of its firehouses began surveys of their territories, including bridges, dams, large buildings and power lines.
"We currently have no reports of damage or injuries," fire department spokeswoman Margaret Stewart said.
Scientists at the California Institute of Technology's seismology laboratory in Pasadena, northeast of Los Angeles, said the earthquake warning system under development for the West Coast gave about 10 seconds of warning before shaking arrived.
Earthquakes of such size occur about once a year in Southern California, according to veteran seismologist Lucy Jones, recently retired from the USGS.
The 96-square-mile Santa Cruz Island is the largest in the chain of eight Channel Islands, five of which are in the national park.
Most of Santa Cruz, including the historic ranch, is owned by The Nature Conservancy, which cooperatively manages the island with the Park Service.
- Press Association and Digital Desk