Bleepers will be used to warn the emergency services and local residents when a big quake is about to strike California. The bleepers will give people 30 seconds warning of the impending tremor.

It may not sound like a lot of time, but Professor Tom Henyey, director of the Southern California Earthquake Centre, believes it could make all the difference.

Tom Henyey: Seconds are vital

"You could shut off gas lines for example," he says. "You could shutdown elevators, you could stop trains on tracks - these are some of the things that could be done within 20 or 30 seconds, if you had that warning."

If you visit Northridge, the Los Angeles suburb in the San Fernando valley, you can still see the scars of the big quake that struck back in January 1994.

Measuring 6.7 on the Richter scale, it was one of the worst natural disasters to strike the United States. 57 people died, a further 1,500 were injured. The fact that the tremor hit at 4:31 in the morning meant there were far fewer casualties than there might have been.

Lucky escape

"The shaking of most earthquakes we have in southern California only last for seconds, literally," says local resident Keith Goldstein, "but this went on for a good 30 to 40 seconds of continual shaking. So we knew a major disaster had happened."

The quake ruptured gas mains

Mr Goldstein was lucky, some of the people who lived next door were not. The multi-storey building collapsed on top of itself.

"The first floor disappeared - the third floor and second floor collapsed and crushed all the first floor units. And that's the building where, ultimately, 16 people died."

While southern California has 18,000 earthquakes a year, most are not strong enough to release the massive stresses that build up underground.

Tom Henyey believes the region will live under the threat of a really "big one" unless more quakes like Northridge ease the pressure.

"We are not having enough modest-sized earthquakes to release that strain so geologists are suggesting we need may be a magnitude seven to get rid of that deficit."