A magnitude 2.6 earthquake that hit Brentwood at 8:45 a.m. Tuesday was 11th aftershock since a magnitude 4.4 temblor struck in nearby Encino a day earlier, seismologists say.
No major damage or injuries were reported immediately following Monday's jolt -- the most significant temblor in Southern California since a magnitude 5.5 earthquake rocked Chino Hills in 2008.
Immediately after Monday's quake, seismologists warned the public to expect aftershocks, with some registering above magnitude 2.0.
Don Drysdale, a spokesman for the California Geological Survey, said "some of them are real little guys," a small group of the aftershocks have been above magnitude 2.0.
The largest so far have been magnitude 2.6, one of which was downgraded from an earlier measurement of 2.7, Caltech spokeswoman Deborah Williams-Hedges said.
Susan Garcia of the U.S. Geological Survey said there were at least four aftershocks in the first 90 minutes after the magnitude 4.4 temblor.
A 5% chance that Monday's earthquake was a prelude to a larger event along the little-noticed fault deep under the Santa Monica Mountains had diminished greatly by Tuesday morning to just 1%.
"As the day goes on, the chances get smaller and smaller," Drysdale said.
Monday's quake surprised seismologists because it was the strongest to hit directly under the Santa Monica Mountains in the 80 years "since we started recording earthquakes in Southern California," Caltech seismologist Egill Hauksson said. Until now, experts recorded only magnitude 1 to 3 quakes there.