Calif. Gets Better, Faster Earthquake Alerts With Upgrade

By Rong-Gong Lin II

California’s earthquake early-warning system is getting a seismic upgrade that will allow residents to receive more timely alerts about shaking from an incoming mega-quake.

How to be Prepared for an Earthquake

GPS data will enable more timely warnings of Earth’s movements that indicate temblors of large magnitude. 

The upgrade would also improve warnings for the Pacific Northwest and California’s North Coast, which are threatened by tsunamis caused by quakes along the Cascadia subduction zone.

The U.S. Geological Survey and its nonprofit partner EarthScope announced the upgraded system.

Let’s say an earthquake on the southern San Andreas fault that starts near the border with Mexico is magnitude 8, but the earliest estimate says it’s magnitude 6.5. The longer that the underestimate is broadcast to phones, the less likely people are to take appropriate action.

“People would react differently — much differently — than if you said it was a magnitude 8,” said David Mencin, vice president of data services for EarthScope, a nonprofit funded by the National Science Foundation, USGS and NASA that’s supplying data for the improved early-warning system.

One of the most famous underestimations came in 2011 with the epic magnitude 9.1 earthquake that triggered a devastating tsunami on Japan’s eastern coast, leaving roughly 18,000 dead.

An initial estimate put the quake’s magnitude at 7.9, meaning the actual earthquake was an astonishing 63 times stronger in terms of energy released.

That underestimation led to a misjudgment of tsunami heights —with some of the first detailed alerts erroneously estimating that the tsunami would be lower than protective seawalls.

Mencin said that had Japan used GPS data, a more accurate magnitude of the quake could have been generated far more quickly.

The USGS’ West Coast earthquake early-warning system has long relied on hundreds of seismic sensors embedded in the ground. However, they can only detect so much shaking quickly.

Hundreds of GPS sensors on Earth’s surface, run by EarthScope, are coming to the rescue now. These sensors usually track very slow movement, in millimeters or less per year.

But in a significant earthquake, the ground moves considerably, permanently, as one piece of land jolts away from the other, moving yards in seconds. 

An earthquake’s magnitude doesn’t appear instantly.

Quakes rupture on a fault at the speed of sound through rock, which is slower than the speed of light in today’s telecommunications systems.

This principle allows people farther from where an earthquake starts to get seconds of warning of the worst shaking to come.

Depending on where people are, some may not get a warning before they feel the first shaking, known as the P wave. But the goal is to give a warning before the most damaging shaking occurs—the S wave, which comes later.

The USGS’ ShakeAlert—which is 90% complete—is expected to have 1,675 seismic sensing stations by the end of 2025.

EarthScope says an additional 1k GPS stations run by the non-profit contribute data to the system. The alerts can be received by downloading the free MyShake app on iOS and Android. Android users are automatically subscribed to Android Earthquake Alerts.

Those systems are set to sound an alarm when an earthquake is estimated to be 4.5 or higher and the expected shaking intensity at the user’s cellphone location.

Stronger earthquakes — magnitude 5 and above — will send users a wireless emergency alert, similar to an “Amber Alert,” if they’re in a location expected to get at least “light” shaking intensity.