An earthquake with a magnitude of 5.3 struck off the coast of Southern California yesterday, officials at the U.S. Geological Survey (USGS) say. The quake originated near the Channel Islands. It happened about 38 miles southwest of the mainland city of Ventura

“A 5.3 is a good jolt,” Dr. Susan Hough of the USGS said at a press conference with Dr. Jennifer Andrews of Caltech, and that it was no surprise people in Los Angeles felt the quake.

“We would expect aftershocks, and there is the potential for some triggered seismicity,” Andrews said.

The quake’s strength was revised upward from initial estimates of magnitude 5.0. It struck about 10.5 miles underground, the USGS said.

Asked was it likely to follow typical aftershock patterns, Hough said “We can never count on earthquakes to obey the averages,” but said they did expect an aftershock pattern, most likely peaking in the magnitude 4 range.

“Earthquakes are not at all predictable. We can say what’s happened in the past, we cannot say what’s going to happen,” Hough said, adding, “There’s always a 1-in-20 chance that an event like this will trigger something bigger.”

An early-warning system did alert residents in Los Angeles before the shaking was felt, Caltech confirms.

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.

Ventura County officials announced they are “in a heightened response posture to assist our citizens,” in the wake of yesterday’s temblor.

Officials took this opportunity to urge residents to make a communications plan if they don’t have one already and to ensure they have emergency supplies on hand.