A strong aftershock from last year's devastating Northridge earthquake jolted the Los Angeles area before dawn Monday, rattling residents' nerves but causing no major damage or injuries.
The quake, which measured 4.9 on the Richter scale, shook millions of people out of their beds, sent water sloshing out of swimming pools, knocked pictures off walls and toppled items from shelves.
It was the biggest aftershock in more than a year from the 6.8-magnitude Northridge quake, which killed 60 people, buckled freeways and caused an estimated $20-billion in damage.
The latest quake struck at 1:40 a.m. PDT and was centered about eight miles south-southwest of Castaic, a small town that lies in rolling hills about 35 miles north of Los Angeles, according to seismologists at the California Institute of Technology.
It was felt up to 200 miles outside Los Angeles and lasted 10 to 20 seconds. Eighteen minutes later, a milder aftershock _ this one with a magnitude of 3.2 _ rumbled through the same area.
Teams of firefighters and police were immediately sent to the streets but reported no structural damage or gas leaks.
The temblor was another reminder of the Northridge quake, which struck before dawn on Jan. 17, 1994, and turned the nation's second largest city into a disaster zone. Experts were not surprised by its strength.
Caltech seismologist Kate Hutton said there had been a 25 percent chance of an aftershock measuring 5.0 or greater this year. "This is just what we would expect after an event the size of Northridge," she said.
Hutton said the Northridge quake has generated more than 10,000 measurable aftershocks, about 60 of them reaching 4.0 or greater, and predicted that the pattern would continue for years to come.
Monday's aftershock was the strongest since a 5.5 quake in March 1994 that caused only minor damage. A 4.5-magnitude aftershock was felt in December.