Quake Swarm Provides a Jolting Surprise

It was another one of those patented early morning Southern California wake-up calls that startled both residents and scientists.

A spasm of Northridge earthquake aftershocks Saturday, the strongest a potent 5.0, awoke much of Los Angeles and Ventura counties and was felt as far away from its epicenter above the Simi Valley as Orange County and the Inland Empire.

Although it caused only very minor damage and no injuries, it brought back troubling memories and a little of the psychological trauma of the devastating Northridge quake that rocked Southern California three years ago.

“It was a very heavy, heavy shaking,” said Simi Valley resident David LaTourette, whose mobile home sustained $20,000 in damage in the Jan. 17, 1994, quake.

“It started out slowly, then all of a sudden it got stronger, and I just thought, ‘Oh God, not another one of these things.’ You never get used to it.”

Three minutes after the initial 5.0, which occurred at 3:37 a.m, a magnitude 4.0 struck.

Law enforcement officials in Los Angeles and Ventura counties said their calls were mainly from people anxious to know about the strength of the aftershocks.

“All that adrenaline and all those fears come back for those people who went through [Northridge],” said Annie Ironside, a dispatcher for the Ventura County Fire Department.

Scientists were somewhat shocked too because they had been saying as long ago as 1995, at the time of the last magnitude 5.0 aftershock, that nothing so strong would be seen again in the Northridge series.

A slightly chastened Jim Mori, scientist in charge of the U.S. Geological Survey’s Pasadena office, said Saturday:

“These predictions we make have to be taken with uncertainty.”

It was only in January that Lucy Jones of the Geological Survey and Caltech seismologist Kate Hutton had said in a written report that “we should expect” only four magnitude 3.0 or larger Northridge aftershocks over the entire next year.

Instead, on Saturday, there were eight such quakes in one day, including six between 3.0 and 3.8, plus the 4.0 and the 5.0. Hutton called herself “mildly surprised,” and Jones confined her comments to a definition of aftershocks.

The magnitude 6.7 Northridge quake killed 72 people, injured more than 11,000 and did more than $40 billion in damage, making it the costliest disaster in U.S. history.

Early morning quakes are nothing new in the Southland.

The Tehachapi quake of 1952 struck at 4:52 a.m.; San Fernando, in 1971, came at 6:01; Landers, in 1992, at 4:58, and Northridge, in 1994, at 4:31.

Saturday’s magnitude 5.0 aftershock arrived even earlier.

It was smaller than the historic quakes, but it woke people up over much of the area, just as the earlier and bigger quakes had.

Saturday’s aftershocks also included a 3.8, a 3.4, three 3.2s and a 3.0., plus two dozen smaller temblors. It was the strongest aftershock series since June 26, 1995.

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Because of their location, centered in a sparsely populated part of the Santa Susanas on the Los Angeles-Ventura County line, seven miles northeast of Simi Valley, there was little appreciable damage.

But seismographic instruments showed that the shaking was quite intense, reaching 14% of the force of gravity near the intersection of Interstate 5 and the Antelope Valley Freeway.

There have now been 13,750 Northridge aftershocks, and, as Jones said Saturday, they will be considered aftershocks as long as the temblors occur within the original rupture zone at a frequency higher than before the original quake.

Saturday’s aftershocks served as an unsettling reminder that California remains “earthquake country.”

Some are used to it. Northridge resident Carol Lackey, 50, knew the quake was not too severe when she glanced at her bedside alarm clock and the digital numbers were still visible.

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“I could see it, so I knew that we at least had power,” she said. “The pitch black in ’94 was the scary thing.”

But unnerved by the moderate temblor was Manisha Hunter, 22, of Van Nuys, who huddled in bed with her two daughters, Jamiesha, 5, and Danisha, 4, and was unable to get back to sleep after a crystal bowl shattered in the shaking.

“The kids got up and came running into my bed,” Hunter said. “It scared me a little because I thought that it was going to be another Northridge earthquake.”

Hunter stroked the girls’ heads until they fell asleep, then carefully took all the belongings off her shelves.

“I went out and moved my car out of the garage just in case,” she added.

Checks by fire personnel, patrol cars and hospital attendants, routine after every significant quake, turned up little damage.

Wendell Mobley, spokesman at Northridge Hospital Medical Center, said the hospital received only minor damage. The facility suffered $18 million in damage in 1994 when it was at the epicenter of the Northridge quake.

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“We had some swing and some creaking and cracking, but nothing serious,” Mobley said of Saturday’s aftershocks.

The Simi Valley’s Lucky supermarket “had maybe three broken bottles, but no other significant damage,” said spokeswoman Judy Decker.

At Magic Mountain in the Santa Clarita Valley, several miles east of the epicenter, mechanics set out at 4 a.m. to test all the rides and found no signs of damage.

“The forces generated each time a roller coaster runs exceed that of most earthquakes,” said Palmer Moody, a park spokesman.

Universal Studios also ran checks on its rides and found no damage.

Both parks opened on their regular schedule.

Contributing to this report were Times staff writers Carlos Lozano, James Ricci and Julie Tamaki, and correspondents Chris Chi, Karima A. Haynes and Coll Metcalfe.