The West Coast's most dangerous faults may rupture 'in rhythm'

"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."

"This behavior has persisted through at least 10 earthquake cycles over the past 3,100 years, according to the study. The study identified matching pairs of sediment layers, also known as doublets, in canyons off Northern California near the Mendocino triple junction, where the San Andreas, Cascadia and Gorda faults converge. Each doublet represents underwater landslides caused by intense shaking, one from Cascadia, followed closely by another from the San Andreas fault."

The Cascadia subduction zone and the northern San Andreas fault have moved in a rhythmic pattern for millennia, with major ruptures on one fault often followed by shaking on the other within minutes to hours. Deep-sea sediment cores from the Cascadia megathrust contain matching pairs of sediment layers, or doublets, in canyons near the Mendocino triple junction. Each doublet records underwater landslides triggered by intense shaking: one attributed to Cascadia and the subsequent one to the San Andreas fault. This partial synchronization has occurred through at least ten earthquake cycles over the past 3,100 years, implying stress transfer between the two systems.

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