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Earthquake early warning system passes major test with quake

March 13, 2013 |  3:07 pm

Anticipating the 'Big One'In the seismic annals of California, Monday’s 4.7 earthquake was little more than a footnote. It gave Southern California a small morning jolt but caused no damage and was largely shrugged off by noon.

But in one important way, the quake was highly significant because it marked an advance in California’s burgeoning earthquake early warning system.

The quake struck in the desert town of Anza, and hundreds of sensors embedded in the ground immediately sent an alert to seismologists at Caltech in Pasadena. They had 30 seconds warning before the quake was felt there.

“It was right,” said Kate Hutton, a seismologist with Caltech. “I sat really still to see if I could feel it and it worked.”

The system has been in place for more than a year. But Monday’s quake offered a rare opportunity to actually see – and feel -- if it worked.

The sensor have warned scientists of numerous quakes, but the vast majority were either too small to feel or too far away to be felt in the Los Angeles area. For example, the sensor gave an early warning of several magnitude 5 quakes last year in Imperial County, but the temblors hit too far away for them to felt in Los Angeles.

The Anza quake was different.

Even though it measured magnitude 4.7, its location on solid granite made the shaking stronger and more widespread. People reported to the USGS that they felt it as far away as Arizona and Central California. At Caltech, computer screens flashed with a 30-second countdown to when the shaking would hit Pasadena. Sure enough, it came on time.

Hutton and other declared the test a success, with some caveats.

The system initially overestimated the quake’s magnitude, saying it was a 5.2. But U.S. Geological Survey seismologist Susan Hough was not overly concerned about the error. She noted that the main job of the system is to alert people to a coming quake, not to gets its magnitude precisely right. The Anza quake caused an unusually intense amount of shaking, Hough added, so the warning system accurately captured that.

The early earthquake warning system is a pilot project for what scientists hope will eventually be a statewide network using thousands of sensors to notify people about imminent shaking from moderate to strong earthquakes.

Backers say an early warning would give utilities time to shut down, trains a chance to slow so they don’t derail and workers a chance to move away from hazardous materials or precarious positions. Warning would be sent to the public through text messages, emails and other special alerts.

Similar systems are already operating in Japan, Mexico and Taiwan. In 2011, Japan’s program alerted about 50 million residents ahead of the devastating Fukushima earthquake.

The warning program’s reliability hinges on where sensors are placed. They need to be located near active fault zones. The Anza quake hit in a seismically active area where officials have embedded many sensors.

Scientists have long believed that a major quake could erupt in the desert and mountain regions north and east of Los Angeles  because the San Andreas and other faults run along there. The Monday quake was along the San Jacinto fault zone.

Hough and others warned that the system would only be effective for quakes some distance from the urban center of Los Angeles.

The warning system works when sensors in the ground detect the first signs of earth movement, known as P waves, that travel at the speed of sound. The more damaging shaking, called the S wave, lags behind at an even slower speed. The greater the distance from the epicenter, the more time population centers would have to prepare. A quake at the the center of the city would provide little to no warning.

“It’s physics,” Hough said. “We have an earthquake like Northridge … those early warnings would not have helped in those places that were damaged.”

Earlier this year, scientists showed off the system using a simulation of the 1933 Long Beach earthquake. A person in Pasadena, 40 miles away, would have about 18 seconds to prepare if an alert was issued.

On Monday, the Anza quake provided a real-life example.

The program is being funded largely from private donations. Scientists are proposing that the state spend $80 million to install and upgrade thousands of the sensors across the state. If they can get the money, seismologists said, the system could be operational in two years.

For all their excitement, Caltech scientists said the system still needs refinement and many more sensors to help detect quakes. The network is fine for seismic experts, but they want to do more work before making it publicly available.

"It’s not ready for prime time. In that sense its being fine-tuned,” Hough said. “Every earthquake is an opportunity to test the system.”

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--Joseph Serna

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