San Andreas, Cascadia faults could combine to set off huge double earthquake, new study finds

"Scientists from Oregon State University studying sediment layers in the Pacific Ocean have discovered that two of the most notorious faults on the West Coast the San Andreas Fault in Northern California and the Cascadia Subduction Zone off Oregon and Washington may be synchronized, with earthquakes on one fault having the potential to set off the other. The study, published in the journal Geosphere, concluded that there are at least three instances in the past 1,500 years, including a most recent one from 1700,"

"The potential linkage between both faults means disaster planners should take into account the possibility of back-to-back quakes, the researchers said Tuesday. We could expect that an earthquake on one of the faults alone would draw down the resources of the whole country to respond to it, Goldfinger said. And if they both went off together, then you've got potentially San Francisco, Portland, Seattle and Vancouver all in an emergency situation in a compressed timeframe."

"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. Major quakes on either of the two faults are rare. But each has the potential to kill thousands of people and cause billions of dollars of damage, previous studies have shown."

Sediment layers in the Pacific Ocean show at least three instances in the past 1,500 years, including 1700, when huge ruptures occurred on both the San Andreas Fault and the Cascadia Subduction Zone within minutes to hours of each other. Evidence indicates a large Cascadia quake triggered the San Andreas in those cases. Major quakes on either fault are rare but capable of killing thousands and causing billions in damages. Potential linkage implies emergency resources could be overwhelmed if both faults rupture in a compressed timeframe, affecting multiple major West Coast cities.

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