>Why not send only to phones currently in and maybe within 250m of those zones? There's often significant lag between the earthquake and the arrival time. You

>Why not send only to phones currently in and maybe within 250m of those zones? There's often significant lag between the earthquake and the arrival time. You don't just want the people in the inundation zone to know, you also want everyone else to know to stay away. That's not just a theoretical edge case. If this had been a major tsunami your system would have killed me just now. I would have been outside of your suggested range and alone at the time of the alert, but was planning to walk my dog along the water front at noon, which was just around the projected arrival time.