Earthquake in Venezuela: how cell phones managed to alert users before the tremors

Video shows moment when building collapsed in Venezuela
Some people in Venezuela received tremor alerts on their cell phones before two earthquakes hit the north of the country last Wednesday (24). The shock left more than 180 dead and 1,500 injured.
The notifications were sent using the earthquake early warning feature available on Android, Google's operating system.
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Venezuelan Jessie Figueira told g1 that she received an alert about 30 seconds before feeling the tremor.
"Near earthquake: you may feel tremors. The estimated initial magnitude is 6.2 at around 357 kilometers away", indicated one of the alerts shared on social media.
Android sent an alert moments before earthquakes in Venezuela
Reproduction
Google explains that it uses its own Android cell phones to monitor tremors around the planet.
"This approach uses the more than 2 billion Android smartphones in use around the world as mini-seismometers, creating the largest earthquake detection network on the planet", says the company on its website.
The company that, since 2021, has identified more than 18 thousand tremors with this mechanism. Around 2,000 earthquakes were intense enough to send alerts and led to 790 million alerts on users' devices.
How Android identifies earthquakes
The system uses the cell phone's accelerometer, a sensor that measures the vibration and acceleration of devices - it is the same one that automatically rotates the screen when the device is turned sideways. Nonstandard records indicate that a place may have been hit by an earthquake.
The signal is sent along with the approximate location to a Google server that combines data from several devices to confirm the tremor.
Building damaged after earthquake in La Guaira, Venezuela
REUTERS/Maxwell Briceno
Notifications are triggered in cases of earthquakes of magnitude 4.5 or greater. In Venezuela, two tremors of magnitudes 7.2 and 7.5 were recorded less than a minute apart in highly populated areas.
In addition to magnitude, Google considers the Modified Mercalli Intensity Scale (MMI), which measures practical effects of earthquakes. The scale goes from 1 to 12, with 1 being unfelt tremors and 12 being tremors with widespread destruction.
Android can send attention alerts, for earthquakes with MMI intensity 3 and 4, as happened in Venezuela, and action alerts, aimed at tremors with MMI intensity above 5, explains Google.
Android sends action and attention alerts through an earthquake detection system
Disclosure/Google

Source: G1