Earthquake Early Warning（在线收听）

The US Government is testing an early warning system for earthquakes, which could buy vital seconds of time in advance of a major incident. For years the US has lagged behind Japan in quake detection technology and it is hoped that this latest system will bring it in line with other quake-prone countries.

Our reporter Li Dong has the details.

 
A map of California with a flashing red dot shows the epicenter of an earthquake. A clock counts down the time remaining before the earthquake strikes and another warning predicts the expected magnitude. The shock waves fan out like ripples on a pond across the state of California.

If this pops up on your desktop at work then you've got just seconds to react... But those seconds could be the difference between life and death.

At the moment the system is still in its development stages, and has not yet been broadcast to California's residents or businesses; but it does represent the future.

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

Since earthquakes are unpredictable, supporters of early warning systems say it's the next best thing available to prepare people and businesses before the ground shakes. Even an advance notice of five seconds can be precious.

Doug Given, of the US Geological Survey explains the importance of an early warning system ... even if it is just a few seconds.

"What can you do with a few seconds warning? The most obvious for the average citizen is to drop, cover and hold on."

Early warning systems are designed to sense the first pulses of energy after a fault breaks and use this to estimate the magnitude of the quake. 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 "P" waves before the secondary "S" waves hit, which can cause buildings to collapse. Doug Given says this is how a warning is issued, ahead of the arrival of these stronger waves.

"So, if you can detect the earthquake very quickly as it begins, you can send warning ahead of the most damaging waves."

But how much warning? Doug Given says the warning could be just a few seconds to tens of seconds; it all depends on the distance from the epicenter. The farther away an area is, the more notice people in that area will receive.

"Depending on your distance from the earthquake, you get from zero up to a minute's warning."

A number of actions can be taken in advance of a quake striking - trains can be slowed or stopped; air traffic controllers can halt takeoffs and landings; power plants and factories can close valves; and schoolchildren can dive under their desks and cover their heads.

Early warnings are useless at the quake's origin because the tremors radiate out almost simultaneously.

But there have been glitches in the system. Sensors underestimated a quake at a magnitude 8.1 when it was actually 22 times stronger.

Because of the error, warnings were not sent to certain cities. The jolt was so violent that it knocked 55 seismic stations offline and there were no warnings sent for aftershocks for several hours.

Since 2006, the U.S. has been testing three alert systems and launched a prototype internally known as "ShakeAlert" in February, a month before the Japan devastation.

For now, messages are only blasted out to about 30 scientists at the USGS, California Institute of Technology and University of California, Berkeley, where they are ironing out software bugs on a small budget.

For CRI, I am Li Dong.