The prototype earthquake-warning system we told you about almost a year ago really works.

It wasn't its first time in action, but Monday's SoCal Anza earthquake put the Caltech-USGS “Shake Alert” system to a high-profile test.

The system's alarm bells rang and as many as 30 seconds warning came to urban L.A. after the 4.7 temblor first started rocking:

It's not really a prediction system. It's a warning system. The way it works — and it only applies to California — is that after a remote quake happens, there's a certain amount of time before it would hit L.A.

The warning counts down that time, graphically so. It's literally like watching as a tsunami heads for us.

In fact, Fox 11 News captured the warning system in action as an Anza aftershock rolled toward us:

Caltech seismologist Kate Hutton told us the system “allowed us to pinpoint the location and measure the size” of Monday's quake.

On Caltech Seismological Laboratory computers “a window pops up on-screen and says how many seconds before shaking,” she said:

We had 20-30 seconds before a wave. We were happy that it worked the way it should. We don't have quakes in the magnitude 4 range all that often.

So far only a select few outside Caltech and the USGS — the Los Angeles' Emergency Operations Center, the California Emergency Management Agency, Google, Bay Area Rapid Transit, utilities such as California Edison — have the warning system.

Hutton says its a few years away from the day when you can log on to a website and watch the Big One roll your way.

“We need to harden the network so it doesn't go down,” she says. “There needs to be more software development. It's thought to be a few years away provided the funding comes through.”

Will the automatic federal “sequester” budget cuts affect the system?

“It does affect the USGS budget,” Hutton says, “but it's not clear yet how it will affect the early warning system.”

[@dennisjromero / / @LAWeeklyNews]

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