If that happens, waves 30 to 100 feet tall could destroy coastal towns in minutes. Even worse, entire communities could sink as the ground suddenly drops several feet, worsening the flooding and leaving people trapped below sea level.

You don’t need to dig far to find proof of past devastation. Walk along the coastline and you might stumble upon “ghost forests”—stands of long-dead trees, their trunks bleached and bare. They’re eerie reminders of the 1700 event, when land dropped and seawater surged in, killing the trees instantly. Native oral traditions and Japanese tsunami records both describe massive waves wiping out entire villages. These natural disasters occur every 300 to 600 years. And if history holds, we’re overdue.

The East Coast, meanwhile, may feel far removed from Pacific threats—but