Two of the West Coast's most dangerous fault lines might be more in sync than scientists have realized. A new study found that the two sleeping giants, the Cascadia subduction zone and the northern San Andreas fault, have been moving in rhythm for millennia, shaking within hours of each other in a geological "dance" that can rattle the coastline from Oregon to California.
The waves followed, reaching Hawaii, California, and parts of Washington. It was one of the strongest earthquakes ever recorded and though early reports show little damage, the event serves as a powerful reminder: Tsunami risk isn't just theoretical.