Two major fault systems along North America's West Coast, the Cascadia subduction zone and the San Andreas fault, may be more closely connected than previously believed. A new study suggests that activity on one fault could trigger earthquakes on the other, raising the possibility of closely timed seismic events.

"We're used to hearing the 'Big One' -- Cascadia -- being this catastrophic huge thing," said Chris Goldfinger, a marine geologist at Oregon State University and lead author of the study. "It turns out it's not the worst case scenario."

Deep-Sea Evidence Reveals a Hidden Pattern

To investigate this possibility, Goldfinger and his colleagues examined sediment cores taken from the ocean floor. These cores preserve about 3,100 years of geological history.…