Wave of Quakes Continues; More May Hit

Another wave of Northridge earthquake aftershocks, the strongest measuring 4.9, struck early Sunday, centered west of the Santa Clarita Valley, and seismologists said the activity may continue--but not exceed the weekend quakes in size--in the days ahead.

Sunday’s 4.9 quake was felt as far away as San Bernardino and Santa Catalina. No injuries were reported, and apart from minor breakage in stores and homes near the epicenter, there was little damage.

At Caltech, scientists said they will examine two active faults, the San Cayetano and the Santa Susana, both in the vicinity of the weekend epicenters, to determine whether the main 1994 Northridge quake has put strain on them that is spawning new ruptures along the fault.

Post-Northridge studies by the Jet Propulsion Laboratory indicate that movement along the San Cayetano fault, which runs from Los Angeles to Santa Barbara County, is compressing the Ventura Basin at a rate that could result in a big quake in Ventura County west of the Northridge rupture zone, said seismologist Egill Hauksson.

But Hauksson cautioned that such an event might not take place “for decades, or even centuries.”

As for the immediate future, Jim Mori, the scientist in charge of the U.S. Geological Survey’s Pasadena office, said there are prospects for a number of “smaller” temblors in the next several days. But he said the chance is only about 5% that one as big as the largest of the weekend quakes will recur.

Of the current spasm of sizable aftershocks that quake scientists had not expected, Hauksson said: “It is complex. One question is, what fault plane, or what fault, is involved?

“The issue is, did the Northridge earthquake leave behind small patches of [the original, subterranean] fault surface that are now breaking? Or have these bigger faults, the San Cayetano and Santa Susana, been loaded by Northridge and begun to break?”

The prospects, he cautioned, are uncertain. “This is at the limits of what quake science understands,” he explained.

A number of scientists are also fearful that the eight significant damaging temblors along the San Gabriel and Santa Susana mountains since 1970--including the Sylmar-San Fernando quake in 1971 and Northridge in 1994--may presage a really big quake along the San Andreas fault, 40 miles northeast of Los Angeles.

They make the comparison to the quakes on the Hayward and other faults in the Bay Area in the decades preceding the great San Francisco quake of 1906. The current scenario too is usually projected in terms of decades, not the next few weeks or months.

Meanwhile Sunday, the director of the Caltech Seismological Laboratory, Hiroo Kanamori, questioned projections by two scientists--one from the U.S. Geological Survey and the other from his own Caltech lab--that only four Northridge aftershocks of 3.0 or larger were expected throughout 1997.

There have been 12 such quakes in just the last two days, including a 5.0, a 4.9, a 4.0 and a 3.0 Sunday evening, and Kanamori said Sunday:

“You can make all sorts of models with many different parameters, but it’s hard to make a definite statement,” like the ones made in January.

One of those scientists, Caltech seismologist Kate Hutton, said Sunday that even though the odds of something happening at broad variance with projections may be small, it does happen sometimes.

“I think the people of California need to be prepared at any time,” Hutton said. “This is a good reminder that the Northridge sequence is not over yet, and it’s a credit to the building codes in California that we can have a 5 magnitude quake without much damage.”

The 4:09 a.m. temblor Sunday was centered a mile northeast of Saturday’s spasm of aftershocks, in the Santa Susana mountains several miles west of the Santa Clarita Valley. It was followed by 3.6, 3.4 and 3.3 quakes in the next four hours.

Altogether, there have been about 60 quakes in the two-day period in the mountains between the Simi and Santa Clarita valleys, most too small to be felt.

Sunday’s quakes, a little closer to populated areas than Saturday’s, may also have done a little more damage. A number of grocery, liquor and convenience stores reported some breakage, as did some homeowners. No injuries were reported.

Sherrie Lander, a manager at Longs Drugs in Valencia, said that when she arrived at the store early Sunday, broken ceiling tiles, glass and merchandise covered the floors.

“Anything liquid--liquor, shampoo--was all over,” she said. “It was a mess.”

At the Hughes Family Market in Stevenson Ranch, an employee said the quake knocked bottles and other merchandise off shelves.

“We couldn’t even walk down the aisles,” he said. However, the 24-hour market never closed, and the cleanup was completed in several hours.

The Ralphs and Vons grocery stores in Newhall also reported falling ceiling tiles and some breakage.

Residents’ reactions to the weekend quakes were mixed.

“With all of the information we have, I think people are mentally prepared for the Big One,” said Jose Haro of North Hollywood. “We just don’t know when it’s going to come, whether it’s today or tomorrow.”

Gene Smith of Northridge, who is finally finishing the repairs to his home from the 6.7 Northridge quake, said the new quakes had given him pause.

“I’m beginning to wonder whether or not it’s worth it to have earthquake insurance on my home, because the deductible is so high,” he said. “Pretty soon, it’s going to be out of reach for most people. Only the very affluent will be able to afford it.”

But some took a brighter view.

Gail Elmore said she had recently moved to Stevenson Ranch from Oklahoma and had been looking forward to her first significant earthquake. Feeling several tremors in the same weekend was a sort of bonus, she said.

“It was kind of neat to see how it felt. It makes you wonder when the next one is coming,” Elmore said. “I’m almost hoping for another one, when I’m more awake.”

The quakes Elmore felt, however, were far less violent than the Northridge quake.

Quake velocity maps released Sunday by the Geological Survey showed the maximum ground movement per second in Saturday’s 5.0 jolt was about three inches. In the Northridge quake, the maximum movement was six feet per second.

Times correspondent Karima A. Haynes contributed to this story.

* QUAKE VICTIMS: Insurance commissioner takes up cause of those who are suing over insurance claims. B1

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Southern California Shaking

This map produced by the U.S. Geological Survey shows the amount of ground acceleration, in centimeters per second, in Sunday morning’s 4.9 quake, centered four miles southwest of Castaic Junction. The contours show more acceleration toward the epicenter. Top acceleration was 100 centimeters, or about 25 inches, per second. Triangles are locations of seismographic instruments.