How was Google able to alert Android users moments before earthquakes hit Venezuela?

Some Android users have claimed Google sent them alerts moments before the two earthquakes of 7.2 and 7.5 magnitude hit Venezuela on Wednesday. Google's Android Earthquake Alerts System uses accelerometers present in smartphones to detect the initial, faster-moving P-wave of an earthquake before the slower and more destructive S-waves hit. It analyses data from multiple devices to send an alert.