Earthquake early-warning system's future still in doubt
Supporters of California's quake early warning system hope this week's success will prompt state officials to help fund completion of the network.
The system currently is being funded as a pilot program, largely by private donations as a temporary project.
Scientists and some lawmakers have called for the state to pay to make the system permanent.
Backers want the state to spend $80 million to install and upgrade thousands of the sensors across California. If they can get the money, seismologists said the system could be operational in two years.
Without the funding, the future of the system is unclear.
Monday's 4.7 temblor in Anza marked a big advance for the system.
The quake struck in the desert town of Anza, about 35 miles south of Palm Springs, 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 Caltech seismologist. "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 — whether it worked.
The sensors 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 sensors gave an early warning of several magnitude 5 quakes last year in Imperial County, but the temblors hit too far away for them to be felt in L.A.
The Anza quake was different.
Even though it measured only magnitude 4.7, its location on solid granite made the shaking stronger and more widespread. People reported to the U.S. Geological Survey 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 others declared the test a success, with some caveats.
The system initially overestimated the quake's magnitude, saying it was 5.2. But USGS seismologist Susan Hough was not overly concerned about the error. She noted 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.
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. Warnings would be sent to the public through text messages, emails and other special alerts.
Similar systems are already operating in Japan, Mexico and Taiwan. Two years ago, Japan's program alerted about 50 million residents ahead of the devastating 9.0-magnitude earthquake.
The warning program's reliability hinges on where sensors are placed. They need to be near active fault zones. The Anza quake hit in a seismically active area where scientists have embedded many sensors.
Scientists have long believed a major quake could erupt in the desert and mountain regions north and east of L.A. because the San Andreas fault and other faults run along there. The Monday quake was along the San Jacinto fault zone.
Hough and others warned the system would be effective only for quakes some distance from the urban center of L.A.
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 waves, lag behind at a slower speed. The greater the distance from the epicenter, the more time population centers would have to prepare. The system would provide little to no warning for a quake at the center of the city.
"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 were issued.
Photo: Seismologist Lucy Jones explains during a news conference at Caltech in January how P waves and S waves are created by an earthquake. Sensors embedded in the ground can detect the waves and provide an early warning of shaking to come. Credit: Anne Cusack / Los Angeles Times