4.9 Earthquake Rattles Much of L.A. County : Geology: Aftershock from Northridge temblor causes little damage and no injuries.

A series of aftershocks from the Northridge earthquake, the strongest a magnitude 4.9, awakened large parts of Los Angeles and Ventura counties early Monday but caused only slight damage and no reported injuries.

Centered on the north side of the Santa Susana Mountains at the northernmost edge of the aftershock zone 40 miles from Downtown Los Angeles, the magnitude 4.9 jolt at 1:40 a.m. was the strongest temblor stemming from the Northridge quake since a 5.2 aftershock March 20, 1994.

Scientists at Caltech and the U.S. Geological Survey, who in January had put the chances of such a sizable aftershock this year at about 25%, said Monday that there is a 10% probability of another such quake in the next year.

One of the scientists, Lucy Jones, said it probably was the last jolt of such size in what she called the “quickly decaying” aftershock sequence after the destructive magnitude 6.7 Northridge earthquake that struck Jan. 17, 1994.

Aside from $150 worth of groceries breaking on the floor at a store in Val Verde, a garage door knocked askew near Six Flags Magic Mountain in Valencia and a few pictures and other belongings falling elsewhere in the Santa Clarita Valley, little damage was reported Monday.

But being roused from sleep by rattling windows and shifting furniture reminded some residents of the Northridge quake and sent some pajama-clad residents running outdoors.

James Cabrera, 13, said residents in his Val Verde neighborhood gathered outside for about 25 minutes following the aftershock, comparing stories and ensuring that nobody was hurt.

He said that another aftershock--measured at magnitude 3.2--that occurred while people were outside was more frightening than its stronger predecessor because residents heard it coming.

Cameron Chesebrough, a visitor from Monterey staying in a camper near the epicenter, said of the 4.9 aftershock, “It was a big shake . . . for like six seconds. I stayed up all night, [but] I felt very safe in my van.”

Alysyn Bullimore, 24, in nearby Castaic, said she went back to sleep. Her 8-month-old daughter, Kendra, slept through the aftershock and awoke only “when I grabbed her. . . . For the first hour I was scared, but then I was like, I have to go back to bed now.”

“It felt like a major tremor to me,” said Dallas Jones, 57, of Valencia, who was five miles east of the epicenter. “I got out of bed like a rocket and started grabbing things.”

Jones said pictures fell off his walls, papers were strewn about his desk and other belongings were jolted from shelves, but nothing was seriously damaged.

It was the 57th Northridge aftershock of magnitude 4 or greater, but 49 occurred in the first two weeks after the main earthquake.

Altogether, Caltech seismologist Kate Hutton said Monday, there have been about 11,500 Northridge aftershocks, the preponderance of them too small to feel and the majority occurring in the first six weeks after the quake.

The strongest jolt Monday was felt as far as Orange County to the south and San Luis Obispo to the north. Altogether, there were 16 aftershocks of varying strengths after midnight Monday.

Jones, Hutton and Caltech seismologist Egill Hauksson issued a statement Monday saying that the Northridge aftershock sequence “is dying off slightly more quickly than average but is also more active than average for California.”

They explained that the aftershock sequence was smaller in the 1971 Sylmar-San Fernando quake, but “even more energetic than Northridge” after the 1933 Long Beach earthquake.

“By fitting an equation to the aftershocks already recorded, we have made estimates of the number of Northridge aftershocks to expect in the future,” the scientists said. “Today’s magnitude 4.9 aftershock is . . . within the expected range of aftershocks, but may well be the largest of the year.”

The scientists added that eight to 10 magnitude 3 quakes may be expected in the next 12 months and one more magnitude 4.

Jones said it is more likely that there will be another magnitude 5 aftershock of the 1992 Landers quake than of Northridge, since the Landers quake, at magnitude 7.5, was far more powerful than Northridge, and its normal aftershock sequence has several more years to run.

Another unrelated earthquake Monday, measured at a mild magnitude 2.7, was centered near San Diego at 5:51 a.m.

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Diminishing Aftershocks A magnitude 4.9 aftershock from the Northridge quake jolted Los Angeles County early Monday morning; it was the strongest aftershock since March of last year. U.S. Geological Survey quake expert Lucy Jones says another aftershock of similar strength is improbable.

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Big aftershocks In the first two weeks after Jan. 17, 1994, main shock, there were 49 aftershocks of 4.0 or greater. A total of 57 of this magnitude have occurred. *

All Northridge aftershocks There hshcsherehave been more than 11,000 aftershocks of the Northridge earthquake; most were too small to be felt and occurred in the first weeks after the quake.