> The alert system works by using your device’s accelerometer to detect the initial, nondestructive P-wave. Your phone then sends a city-level location, which does not include zip code or street address, to Google’s earthquake detection server. The reports get verified before a loud notification that includes a map, magnitude, and basic drop, cover, and hold reminders is sent. It hopefully comes a few seconds before the destructive S-wave arrives

So what is significant is that it does not rely on existing earthquake early warning detection system built by governments but instead of using the cellphone as sensors.