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Android phones around the San Francisco Bay Area buzzed Tuesday morning with a warning: An earthquake measuring 4.8 on the Richter scale was about to hit. “Maybe you felt your shaking,” some posts read. More than a million Android users saw the warning. And for some, it arrived seconds before the ground even started moving.
It’s not the first time Android devices have received these alerts, said Marc Stogaitis, the project leader of the Android Earthquake Alerts System. But because the Bay Area is so densely populated, the alarm hit enough phones that the wider public took notice. Earthquakes have historically come without warning, taking people by surprise and allowing them to fall and take cover without warning. Warnings like these are meant to take away some of the unpredictability of earthquakes, even if it’s just a few seconds.
“One of the things we’re trying to do is build an earthquake early-warning industry,” said Robert de Groot, who is part of the ShakeAlert operations team, a United States Geological Survey project that monitors the early signs of earthquakes. detects. “We do things that we never really thought about.”
The technology doesn’t predict earthquakes — no one can, and the USGS also says it doesn’t think it will learn to predict earthquakes “within the foreseeable future.” But it detects them earlier than people usually feel them. And experts hope that one day the alerts can be sent even faster, giving people more time to get out of the danger zone.
Time to roll
Tuesday’s Android warning was powered by data from ShakeAlert, which detects when an earthquake starts on the West Coast and passes the information on to government agencies and third parties. And Google has taken steps to make that information more easily available in those precious seconds. First, the company has rolled the alert into its own system, sending push notifications to people with Android phones who are near an earthquake without having to download a separate app.
Here’s how it works: When an earthquake happens, it sends softer seismic waves, known as P waves, through the ground. Not everyone in the area of the earthquake will feel it, but a network of 1,300 USGS sensors will. When four sensors are activated at the same time, they send an alert to a data processing center. If that data meets the right criteria, the ShakeAlert system determines that stronger S-waves are on the way, the kind that can harm and hurt people. It’s then that alert systems, like Google’s, an app called MyShake, or government agencies like the Federal Emergency Management Agency and transit systems, interpret the data and send alerts.
There are limitations. Those S waves move fast; the closer a person is to the earthquake, the less likely they are to get a warning before they feel the shaking. The USGS sensors are expensive and strategically placed on the west coast. (By 2025, there will be 1,675 in total, de Groot says.) The fast-compound magnitude measurements are also only preliminary; Tuesday’s Android warning warned of an impending 4.8-magnitude earthquake, but the reading was later adjusted to 5.1.
Google has also turned individual phones into miniature earthquake sensors. All smartphones have accelerometers that can pick up signals from an earthquake. When the phone is activated, the phone sends the message to a discovery server, along with raw location data, such as the city in which a device is located. The server then compiles where the earthquake is happening based on data collected on multiple phones and broadcasts the relevant alerts.
Stogaitis says phones only pick up the waves when they’re plugged in and locked. That helps avoid confusion from phones rummaging around in bags and pockets. The long-term goal is to transmit signals with even more speed. “We try to make the time from which [an earthquake begins] and the time we detect it and send an alert as soon as possible,” Stogaitis says.
Equipping phones to pick up signals is a cheaper and faster solution than planting larger sensors 10 feet underground in other earthquake-prone areas. But it’s one that requires people and their phones to be closer to the earthquakes, de Groot says, and that’s not always the case. Yet all of these sensors — underground and in your pocket — are giving off new and unprecedented warnings and crucial seconds to drop and cover, something people need to do ASAP. People usually only feel an earthquake when it has already happened, says de Groot. “You are now in a situation, you are now in the middle of it. But doing something before the shaking arrives is something that is relatively new. So we are really looking for the best way to [get people] to do that.”
This story originally appeared on wired.com.
