Mexico’s earthquake early warning system may have helped save lives in the Sept. 19 earthquake. Sirens in Mexico City sounded seconds before the earthquake struck the city, giving a brief window to shut down vital infrastructure and evacuate buildings. There was more warning, about 90 seconds, before the larger earthquake that occurred off the coast of Mexico Sept. 8.
A similar system has been tested for the U.S. West Coast including California and is expected to begin limited public operation in 2018.
What Is EEW?
It’s important to note the difference between Earthquake Early Warning (EEW) and “earthquake prediction,” said Louise Kellogg, professor of earth and planetary sciences.
“EEW is based on detecting an earthquake when it happens, and then sending information about where to expect shaking,” she said. The warning system does not predict where and when an earthquake will occur in advance.
EEW relies on the fact that we can send information at the speed of light, faster than earthquake shaking is transmitted through the Earth. Depending on how far you are from the epicenter, that can give you seconds to minutes of warning. Some locations in California could receive up to a minute of warning. But even a few seconds warning is enough to shut down trains and protect infrastructure such as power grids.
“Earthquake early warning works best if the earthquake source is far away. Then there is more time to assess the event size and estimate shaking intensity,” said Mike Oskin, professor of earth and planetary sciences. “In California, it is more challenging than Mexico or Japan, because we have built our cities right atop shallow earthquake sources of the San Andreas fault system.”
Japan has a similar early warning system that provided helpful warning of the magnitude earthquake in 2011, said John Rundle, professor of physics and earth and planetary sciences.
“Our problem is that we live right on top of the faults, so warning would be a few tens of seconds at best. In Japan, the major quakes are offshore so they have tens to a hundred or more seconds of warning.”
‘The lesson for California is that sometimes EEW will work well, say for a large event that starts far away from an urban area. But in the event of a direct hit – a shallow, large earthquake beneath an urban area – there will be no warning for the area most heavily damaged,” Oskin said.
ShakeAlert (West Coast EEW system)
Seven Steps to Earthquake Safety (California Earthquake Authority)