In an article published in the journal Science, a Google research team and researchers from the University of California, Berkeley, and Harvard University (USA) describe how they implemented the "Android Earthquake Alert" (AEA) system for Android phones between 2021 and 2024.

Androids represent 70% of smartphones worldwide and have a built-in accelerometer by default, which the AEA system uses in its detections.

According to the article, during the analysed period, the system detected an average of 312 earthquakes per month in real time, with magnitudes ranging from 1.9 to 7.8, and sent alerts to users in 98 countries associated with 60 earthquakes with magnitudes greater than 4.5.

On average, Android phones sent 18 million alerts per month between 2021 and 2024, according to data from the article, cited by the Spanish news agency EFE.

To evaluate the effectiveness and user response to these alerts, the authors explain how the system collects voluntary feedback through surveys, which were then analysed.

These assessments indicate that 85% of Android alert message recipients experienced earthquakes. Of these, 36% received the alert before noticing them, 28% during the earthquake, and 23% after the earthquake began.

Experts explain that as soon as an earthquake occurs (a phenomenon that cannot be predicted), seismic waves begin to propagate from the epicenter, being detected on the Earth's surface and measured by seismometers.

The researchers implemented an application on the Android system that, while the phone is idle, if the accelerometer detects the passage of seismic-like waves, sends a message to Google servers with the phone's location and information.

When the servers receive this information from multiple phones, they are used as a sort of basic seismometer network that allows the location of the earthquake's source and magnitude to be determined.

Google uses this information to send an alert to all phones located in the potentially affected area, similar to how Civil Protection agencies in several countries send alerts.

Because seismic waves propagate at high speed, within seconds, the criteria for sending an alert are automatic and do not depend on the decision to send an alert, as is the case with Civil Protection messages, for example.

The study authors say they "believe the system supports efforts to improve detection with rapid, large-scale data collection and feedback to algorithms."

"In a significant proportion of cases, especially those farthest from the earthquake's origin, the phone alert arrives before the seismic waves themselves, giving the recipient a few seconds to protect themselves," explained Galderic Lastras, a geologist at the University of Barcelona, in a response reported by the Scientific Media Center (SMC Spain).