The big one might not come alone: Double West Coast earthquake threat

Two of the most dangerous fault systems on the U.S. West Coast may be more connected than scientists once thought. New research suggests the Cascadia subduction zone and the San Andreas fault can sync up, triggering earthquakes within minutes or hours of each other. This rare synchronization could dramatically increase the scale of a major West Coast disaster. Instead of one massive quake, multiple regions could be hit at nearly the same time.