The “big one” might not come alone: Two major West Coast faults may strike back to back

Two of the most closely watched fault systems on North America's West Coast may be more connected than scientists previously realized.

A recent study suggests that the Cascadia subduction zone and the San Andreas fault can become synchronized, with a major earthquake on one fault potentially followed by seismic activity on the other. In some cases preserved in the geologic record, the two systems may have ruptured only minutes or hours apart.

"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."

To investigate the relationship between the faults, Goldfinger and his colleagues studied deep sea sediment cores containing about 3,100 years of geologic history.