Seismologists studying swarm of earthquakes in Southern California

Experts said the cluster of earthquakes that began Tuesday night are far from out of the ordinary for Southern California, but that the region has not seen this type of sequence in a few years.

At a news conference Wednesday morning, Kate Hutton of the U.S. Geological Survey at Caltech said there had been at least 30 quakes since Tuesday night, but only three could be felt by residents. She said officials are studying the quakes to understand whether it was a swarm or some other type of pattern.

"This is all part of the same earthquake sequence; they're all in the same area,'' Hutton told reporters at the briefing. "We haven't had anything in the L.A. Basin in the last few years, but that doesn't mean we're totally quiet, and we certainly have been active in the southern part of the state,'' she added.

The quakes jolted residents but caused no major damage.

"It shook us pretty good. We’ve felt earthquakes before, so it came as no surprise,” said Chris Nordyke, director of marketing at the Richard Nixon Library and Birthplace in Yorba Linda. “It shook open the door but nothing fell off the shelves.”

He said an inspection of the facility is underway.

Law enforcement officials in Orange County said there were no immediate reports of damage from the earthquake that hit near Yorba Linda about 9:30 a.m. (The Wednesday morning quake was initially downgraded to 4.1 but then upgraded back to 4.5.)

Lt. Santo Porto of the Brea Police Department, which serves that city and Yorba Linda, said police had evacuated the department to check the structure but found no problems. “There’s no damage in either city that we’ve heard so far,” he said.

Orange County sheriff’s officials said they had received no initial damage reports, either.

The series of quakes — including the 4.5 quake Wednesday morning and 4.4 quake Tuesday night — has rattled residents in the area.

“No one really freaked but everyone sure felt it,” said Roxann Reeves, supervisor at a Starbucks on Yorba Linda Boulevard, where about 20 customers were in line when the aftershock hit. “We’d all just been talking about the one last night.” 

The first earthquake hit near Yorba Linda at 11:23 p.m. Tuesday; the second — upgraded from an initial magnitude of 2.2 — followed about a minute later, according to data from the U.S. Geological Survey. About a dozen aftershocks ranging from magnitudes of 1.2 to 2.2 rumbled the same area until about 3 a.m. Wednesday.

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— Rebecca Trounson, David Zahniser, Richard Winton and Kimi Yoshino