Among their many applications, smartphones can now act as rudimentary seismographs, capable of warning users of an impending earthquake. Google has turned more than two billion Android devices into early warning systems by harnessing the phones’ motion sensors to detect seismic activity.
“Using aggregated measurements from a global network of Android smartphones, we developed a system that detects earthquakes, delivers early warnings to users, and builds user trust with each successful alert,” said Marc Stogaitis, Google’s principal software engineer for Android.
Earthquakes occur frequently across the globe. Each year, millions of small quakes—magnitude 2.5 or less—go unnoticed by people. At the other end of the spectrum, roughly a dozen earthquakes annually reach magnitudes of 7.0 to 7.9. These are considered major, with the potential for severe damage. One or two each year typically reach 8.0 or higher, with catastrophic consequences.
“The accelerometer in an Android phone—the same sensor that flips the screen when it’s turned sideways—can also detect the ground shaking from an earthquake,” Stogaitis said. “If a stationary phone detects the initial, faster-moving P-wave of an earthquake, it sends a signal to our earthquake detection server, along with a coarse location of where the shaking occurred. The system then quickly analyzes data from many phones to confirm that an earthquake is happening and estimate its location and magnitude. The goal is to warn as many people as possible before the slower, more damaging S-wave of an earthquake reaches them.”
Google began rolling out earthquake alerts through Android phones in April 2021, first in New Zealand and then in Greece. By the end of 2023, the system was active in 98 countries. Since its launch, it has detected more than 18,000 earthquakes—from those barely perceptible to humans to major events measuring as high as magnitude 7.8. Alerts have been issued for more than 2,000 of those quakes, resulting in 790 million alerts sent to phones around the world.
“The impact has been a ~10x change in the number of people with access to EEW (Earthquake Early Warning) systems. In 2019, only about 250 million people had access. Today, thanks in large part to the Android system, that number has increased to 2.5 billion,” Stogaitis said.
The defining benefit of EEW systems lies in the seconds they buy before strong shaking begins. Those few moments can be enough to seek cover and avoid injury. According to the U.S. Geological Survey, people should take shelter under a desk or table and hold on, or move to a hallway or against an interior wall. Areas to avoid include spots near windows, fireplaces, heavy furniture and appliances. Running down stairs or fleeing buildings during the shaking is discouraged, as is taking cover under bridges, trees, signs or power lines if driving. In mountainous areas, falling rocks or landslides are also hazards.
In California, Oregon and Washington, Google partners with the USGS, which manages ShakeAlert, a government-backed early warning system. The system relies on a network of 1,675 seismic sensors that detect ground movement, then calculate the earthquake’s size and location. ShakeAlert sends that information to the Android Earthquake Alerts System, which then delivers notifications to Android users in the affected areas.
Outside the U.S., Google employs a crowdsourced approach. All smartphones contain tiny accelerometers that can sense vibration. When a phone detects shaking it believes may be caused by an earthquake, it sends data—including an approximate location—to Google’s earthquake detection servers. If enough phones detect similar movement in the same area, the system determines whether an earthquake is occurring. This decentralized approach effectively turns more than 2 billion smartphones into mini-seismometers, forming the world’s largest earthquake detection network.
Determining an earthquake’s magnitude in real time remains a challenge. The magnitude dictates how far shaking will travel—and who needs to be warned. Getting that calculation right is essential. Underestimating the magnitude could leave people in danger; overestimating may result in false alarms, which erode public trust.
“The challenge lies in the trade-off between speed and accuracy. The first few seconds of an earthquake provide limited data, but every second you wait to issue an alert is a second less of warning for those in the path of the shaking,” Stogaitis said.
Still, the technology has advanced. During a magnitude 6.7 earthquake in the Philippines in November 2023, the first alert was sent out just 18.3 seconds after the quake began. People nearest the epicenter received up to 15 seconds of warning—just enough time to duck for cover. Those farther away had up to a full minute to act. But the warnings can go further than that, according to ShakeAlert. “These automated actions could include slowing trains, closing water valves, turning on backup generators, issuing public announcements, and many others.”
