Why Google's earthquake alerts didn't reach your phone

Google's earthquake alert system has specific parameters designed to avoid unnecessary panic, meaning smaller tremors won't trigger notifications.

The system, known as the Android Earthquake Alerts System, operates with two notification levels. The 'Be Aware' alert is sent for earthquakes of magnitude 4.5 or higher, signaling a mild tremor that is unlikely to cause major damage. A more urgent 'Take Action' alert is reserved for earthquakes of the same magnitude but with an estimated intensity of moderate to strong shaking. This higher-level alert overrides 'Do Not Disturb' modes, emits a loud sound, and displays full-screen safety instructions.

The decision to set the lower limit at magnitude 4.5 is rooted in the minimal energy released by smaller earthquakes. A magnitude 2.9 tremor, for instance, is typically only felt by individuals very close to the epicenter and poses no significant risk or structural damage. Issuing mass alerts for such minor events would desensitize users to notifications, diminishing the system's effectiveness during genuinely dangerous seismic activity.

Android phones detect earthquakes using built-in accelerometers that identify primary seismic waves (P-waves). When thousands of phones in a concentrated area simultaneously detect these vibrations, Google's servers process the data rapidly. They pinpoint the epicenter and estimate the magnitude, subsequently issuing alerts to phones in areas expected to experience secondary seismic waves (S-waves), which are the most destructive. This mass data processing requires a sufficiently strong and widespread movement to be registered across multiple devices, confirming a real risk before an alert is sent.