- Associated Press - Tuesday, September 20, 2011

PASADENA, CALIF. (AP) - Elizabeth Cochran was sitting in her office when her computer suddenly sounded an alarm.

Beep. Beep. Beep.

A map of California on her screen lit up with a red dot, signaling an earthquake had struck. A clock next to the map counted down the seconds until shock waves fanning out from the epicenter north of Los Angeles reached her location in Pasadena: 5-4-3-2-1.

Right on cue, Cochran felt her chair quiver ever so slightly from a magnitude-4.2 that rumbled through Southern California on Sept. 1.

“If I hadn’t known it was an earthquake, I would have thought it was a truck going by,” she said.

After years of lagging behind Japan, Mexico and other quake-prone countries, the U.S. government has been quietly testing an earthquake early warning system in California since February. Cochran belongs to an exclusive club of scientists who receive a heads up every time the state shakes.

The alert system is still crude and messages are not yet broadcast to residents or businesses.

With more testing and funding, researchers hope to build a public warning system similar to the Japanese that has been credited with saving lives during the March 11 magnitude-9 disaster.

Since earthquakes are unpredictable, supporters of early warning say it’s the next best thing to prepare people and the commercial sector before the ground rocks. Even a 5-second advance notice can be precious, they contend.

“You want to get under a sturdy table before things start falling off the wall,” said University of California, Berkeley seismologist Richard Allen, a project participant. “We don’t want people to start running out of buildings.”

Early warning is designed to sense the first pulses of energy after a fault breaks and estimate the magnitude based on limited information. This is possible because of the different speeds at which seismic waves travel.

A sprawling web of underground sensors can detect the faster-moving and less damaging primary or “P” waves before the secondary “S” waves that can cause buildings to pancake. A warning is issued ahead of the arrival of the stronger waves.

How much warning _ a few seconds to tens of seconds _ depends on the distance from the epicenter. The farther away, the more lead time.

Project chief Doug Given of the U.S. Geological Survey ticked off actions that can be taken: Trains can be slowed or stopped. Air traffic controllers can halt takeoffs and landings. Power plants and factories can close valves. Schoolchildren can dive under their desks and cover their heads.

Early warning is useless at the quake’s origin because the tremors radiate out almost simultaneously.

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