Mysterious Jolts Shake Residents Near Coast : Post-quake jitters: Experts detect no ground movement, and police and military officials are at a loss to explain Saturday’s two blast-like concussions.

Car alarms wailed and at least five storefront windows shattered--but the concussive jolts that many along Orange County’s coast experienced shortly after noon on Saturday were not another earthquake.

“There’s absolutely, positively, no earthquake,” said Doug Smith, a spokesman for the California Institute of Technology in Pasadena. “There’s been no ground motion. You’re free to speculate what it was.”

Military, police and other officials could offer no explanations as to the cause of the two blast-like vibrations, felt about 12:30 p.m., most acutely in Corona del Mar, Newport Beach, Costa Mesa and Huntington Beach.

With sensitivities heightened by Friday’s deadly, 6.0-magnitude Sierra Madre earthquake, many suspected that Saturday’s events were aftershocks. But Caltech’s Smith said Saturday that the last recorded aftershock occurred at 12:53 p.m. Friday.

“Everybody’s been real jittery,” Smith said, referring to the stream of calls to Caltech’s seismology lab after Saturday’s unexplained events.

Although no injuries were reported on Saturday, the events were no joking matter to Orange County residents and merchants.

“They have been hearing booms and feeling tremors,” said Costa Mesa Police spokeswoman Jeanette Chervony. “The boards lit up. We’re telling them we don’t know what happened.”

The jolt was especially felt at Great Lengths for Hair, a Corona del Mar salon on Coast Highway.

“We were just working away cutting hair,” said salon owner Bill Cacache.

”. . . the plate-glass window in front of our shop just shattered and fell down.” Cacache said that it would cost $1,100 to replace the 10-by-8-foot window.

On the Balboa Peninsula, surf-wear shop owner Brian Boyle said three of his large storefront windows, worth $1,500, were shattered.

“It was kind of like a whiplash,” said Boyle, whose Main Street Emporium is on the ground floor of the Balboa Inn, at 105 Main St. “It seemed like the whole building rose up off the ground and slammed back down. It was amazing. Everybody just scattered from the store. The people in the dressing rooms were the ones most freaked out.”

In Huntington Beach, another window shattered at a Lucky supermarket on Atlanta Avenue, a store representative said.

In Newport Beach, the midday shake prompted a flood of calls to police.

“We had a number of (car) burglar alarms go off, all at the same time,” said Police Sgt. Kent Stoddard. “The whole (police switchboard) lit up for about five minutes. . . . We felt something here. I don’t know what it was. It felt like our interior windows rattled more than the floor rattled.”

If not an earthquake, was it a sonic boom?

“We haven’t heard anything,” said Lance Cpl. Richard Jacques, the only official who could be reached for comment at El Toro Marine Corps Air Station.

The event also puzzled U.S. Coast Guard radioman Mike Walters, who said the “real bad” window-rattling at his station in San Pedro could not be attributed to any military exercises that he was aware of.

“We’re all wondering the same question,” Walters said. “Was it an earthquake or what?”

At the Newport Beach lifeguard headquarters, safety officer Eric Bauer said he, too, was jolted to attention.

“We heard a couple of booms--they sounded like sonic booms,” said Bauer, whose offices are at the Newport Pier. “Is the space shuttle flying around today?”