Possible Cascadia and San Andreas fault link

A new study published in the Bulletin of the Seismological Society of America shows a possible link to seismic activity in the southern Cascadia Subduction zone and the northern San Andreas fault.

Seismic activity in southern Cascadia has a recurrence interval of approximately 220 years, while the northern San Andreas has a recurrence interval of approximately 200 to 240 years. Researchers at Oregon State University identified 15 turbidites in northern California associated with activity on the San Andreas fault. Of these 15, 13 of them occur at virtually the same time as earthquakes in the Cascadia subduction zone.

In a parallel study, they found that during the same period, 13 of these 15 San Andreas earthquakes occurred at almost the same time as earthquakes along the southern Cascadia Subduction Zone, which stretches from northern Vancouver Island to northern California. The marine and land paleoseismic record suggest a recurrence rate of approximately 220 years for the southern Cascadia fault, which is substantially shorter than the 600-year cycle suggested by previous research for full ruptures in Cascadia.

The Cascadia earthquakes also preceded the San Andreas earthquakes by an average of 25 to 45 years. “It’s either an amazing coincidence or one fault triggered the other,” said Goldfinger. The generally larger size of the Cascadia earthquakes, and the timing evidence suggests Cascadia may trigger the San Andreas Two seismic events on the San Andreas were apparently not associated with Cascadia, including the 1906 earthquake which followed the previous Cascadia earthquake by approximately 200 years.

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