California is earthquake country, and residents of Los Angeles can now get some critical warning, when conditions are right, after a quake has started and seismic waves are heading their way.

The system, called ShakeAlertLA, is the first of its kind in the United States.

Earthquake alert systems like this save lives, said Jeff Gorell, deputy Los Angeles mayor for public safety, as he demonstrated the application on his smartphone. 

“When an earthquake starts, the first waves that go out are called P-waves,” he said. They serve as a warning and “are not the damaging, destructive waves” that will follow. 

The alert system, which relies on data from seismic sensors throughout the region, could offer up to 90 seconds of warning for quakes of magnitude 5 or larger.

Even a few seconds can make a difference, said Los Angeles Mayor Eric Garcetti, as he rolled out the ShakeAlertLA smartphone app in January. Alerts let people know to drop, cover and hold on, as they are instructed to do in earthquakes.

Mexico City system

An alert system is in place in Mexico City that let residents brace for a mild shaker in early February after an earthquake struck Chiapas to the south. The quake was barely felt in the capital, but residents were ready.

The system doesn’t always help, however, and it did not with the magnitude 7.1 earthquake on Sept. 19, 2017, that killed hundreds in and around the Mexican capital. The quake’s epicenter was too close to offer warning.

Distance to epicenter crucial

Alert systems work when there’s enough distance between the earthquake’s epicenter and a center of population, said Thomas Heaton, professor of engineering seismology at the California Institute of Technology (Caltech).

“So, if you can recognize that an earthquake has started … you can give some area that’s about to be shaken strongly a heads up that says, ‘There’s an ongoing earthquake, and oh, by the way, it’s headed in your direction.’”

California is riddled with geological fault lines that periodically rupture. The largest, the San Andreas Fault, can give rise to massive temblors, including the San Francisco quake in 1906, which may have killed 3,000, according to later estimates.

A section of the same fault shifted in 1989, causing a magnitude 6.9 earthquake that killed more than 60 in Oakland and nearby communities. Smaller fault lines can also cause large temblors, including a previously unknown fault beneath the Northridge section of Los Angeles, where a magnitude 6.7 quake killed more than 60 people in 1994.

The ShakeAlertLA app offers users critical information after a temblor has started, said Deputy Mayor Gorell, “just enough so that they can digest it and then react to it, without overwhelming them with information or frightening them,” he said.

Advanced alert systems are also in place in Japan, and while the systems have limitations, authorities there say they have saved lives.

Los Angeles officials say preparing for earthquakes requires work on many fronts, including encouraging residents to prepare disaster plans and stock emergency supplies.

Preparations also require upgrades to old buildings. Los Angeles now has nearly 13,000 so-called soft-story buildings, with wide windows or doors on lower floors that need bracing. These buildings are vulnerable to damage or collapse if struck by seismic waves of a certain type or intensity.

Nearly 1,700 buildings have been upgraded to modern earthquake standards, and another 3,500 have been issued permits for retrofitting. It’s a race against time, officials say, because massive shakers rock the region periodically. The last big quake in Southern California, in 1857, reached magnitude 7.9, and could have killed thousands in a modern city.

The alert app can help, said Heaton, who noted that when the ground “starts to shake, you have no idea whether it’s going to get bigger, or whether it will stay small. Usually it stays small,” he said, “but you don’t know.”

Heaton said the system will give you an indication of what to expect, and also let emergency workers know where to send help after a quake has struck.

ShakeAlert is being rolled out in phases in the U.S. West Coast states of California, Oregon and Washington, which are all vulnerable to earthquakes.
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