San Francisco/Washington - A brief earthquake rattled Los Angeles on Tuesday, causing downtown buildings to sway, sending a jolt to outlying areas and causing parents to rush to schools to check on their children.
The US Geological Survey said the quake was a magnitude 5.4 on the Richter scale, after earlier saying it had been as strong as 5.8.
There were no reported injuries and limited property damage. The temblor lasted several seconds, causing some items to tumble off shelves and popping a waterline at a traffic intersection in Chino Hills, the epicentre of the quake some 50 kilometres southeast of downtown Los Angeles, broadcast reports said.
On the scale of things, it was a moderate to small quake, and seismologist Kate Hutton said the most interesting thing about it was 'that it's the first one we've had in a populated area for quite a long time.'
'Look at it as a drill for the big one that will come some day,' said Hutton, a seismologist with the US Geologic Survey, who spoke in broadcast remarks.
But she attributed the lack of extensive injuries and damage to California's rigid building requirements.
'There are parts of the world where 5.4 can be serious,' she said. 'If there are no (building) requirements, there can be collapses.'
The quake was followed by 27 aftershocks, including the largest of 3.6 magnitude. Asked if it could have been a foreshock of the huge quake expected along California's San Andreas fault by 2037, Hutton said there was only a 5 per cent chance.
After 24 hours, the chance would drop to 1 per cent. She said that the quake did not appear to be aligned with any of the major faults, such as the San Andreas fault.
The temblor hit about 1842 GMT, and struck at a depth of about 11 kilometres.
A CNN reporter who happened to be at Disneyland in Anaheim said a roller coaster rails swayed back and forth, and the ride was closed down.
Local airports were closed for a brief time and terminals were cleared, but resumed operations soon afterwards, broadcast reports said. A routine inspection of bridges and other infrastructure was expected to follow.
Telephone communications and electricity were briefly interrupted in some areas and trains were shut down for a short time, a Los Angeles city official said in broadcast remarks.
California's last major earthquake was a 6.7 magnitude shake in 1994, when 60 people were killed, 20,000 left homeless and 40,000 buildings damaged.
Earlier this year, a team of federal and state earthquake scientists said an earthquake measuring 6.7 or more was 99 per cent likely to hit California by 2037. A quake rated at 7.5 magnitude was 46 per cent likely.
Hutton said there was literally no warning of Tuesday's quake, as it hit directly in an urban area. She said seismologists were more able to give warnings if a quake starts further away from an urban area.
The San Andreas fault poses one of the greatest worries for California, running a length of 1,300 kilometres through California and forming the tectonic boundary between the Pacific and North American plates.
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