The phones that detect earthquakes

The technology we carry about in our pockets is assisting in the creation of the largest earthquake detection system in the world, fifty years after the first mobile phone call.

California's Bay Area was shaken by a 5.1-magnitude earthquake on October 25, 2022. Fortunately, it wasn't a particularly strong tremor, but reports from locals all across the area who had felt it poured into the United States Geological Survey (USGS). Although there were no reports of damage, the earthquake was notable in another aspect since many locals got notifications on their phones before the shaking began.

More importantly, many of these phones contributed to the earthquake's first detection.

In order to create an early warning system that informs users of earthquakes just a few seconds before they occur, Google has been collaborating with USGS and researchers at a number of Californian colleges. Although the window of warning is small, a few seconds can provide you enough time to find cover behind a desk or table. Additionally, it may be long enough to slow down trains, halt planes from taking off or landing, and prevent vehicles from passing through bridges or tunnels. As a result, when greater earthquakes strike, this technology may save lives.

Two sources of data are used. Seismologists from the USGS, the California Institute of Technology, the University of California Berkeley, and the state government constructed a network of 700 seismometers—devices that detect ground tremors—across the state. (Seismometers in two other US states – Oregon and Washington – also feed into the system, known as ShakeAlert.) However, Google has also been using publicly available smartphones to build the greatest earthquake detection network in the world.

The hardware that senses when a phone is being moved, known as an accelerometer, is built into the majority of smartphones running Google's Android operating system. These are often used to instruct the phone to switch from portrait to landscape mode when it is tilted, for example, and also assist in giving Google's built-in fitness tracker information about the number of steps taken.

The sensors, however, may also function as a miniature seismometer and are remarkably sensitive.

If a user's phone detects vibrations that are indicative of the Primary (P) waves of an earthquake, Google has implemented a feature that enables automatic data transmission to the Android Earthquake Alerts System. The technology can determine whether and where an earthquake is occurring by merging data from hundreds or even millions of other phones. In order to provide an early warning, it may then send warnings to phones in the vicinity of where the seismic waves are anticipated to land.

Additionally, because radio messages move more quickly than seismic waves, notifications can reach distant locations before the shaking begins.

We're literally competing the speed of light (about the speed at which phone signals travel) against the speed of an earthquake, said Marc Stogaitis, an Android software engineer. Fortunately, the speed of light is considerably faster for humans.

The technique makes it possible to watch for earthquakes in locations without vast networks of expensive seismometers because the majority of the data is generated by the public. It increases the likelihood of sending earthquake notifications to even more isolated and underdeveloped parts of the planet.

As the seismic waves propagated outwards from the epicentre in October 2022, Google engineers observed phones lighting up with earthquake detection data all throughout the San Francisco Bay Area.

These vibrations are frequently picked up by the present system. The ShakeAlert system most recently detected an earthquake of magnitude 4.5 on the afternoon of April 4, 2023, close to Tres Pinos, California, and sent alerts to nearby users' mobile phones. In California, where there are up to 100 little quakes every day, earthquakes are frequent occurrences. They are typically too tiny to feel. However, California experiences many earthquakes of greater magnitude annually—roughly 15-20 are greater than magnitude 4.0.

The Earthquake Alerts System is already available in more than 90 countries that are highly vulnerable to earthquakes, and of the estimated 16 billion mobile phones in use worldwide, more than three billion run Android.

However, the system has its drawbacks, especially in distant locations with few phone users and when quakes occur offshore where they might cause tsunamis. And while technology can assist in sending out signals a few seconds beforehand, the science of accurately forecasting earthquakes remains as elusive as ever.