Odds of magnitude 9 earthquake that would devastate West Coast spike after unusual finding: study

The West Coast’s worst nightmare may not end with one catastrophic earthquake.Scientists have uncovered evidence suggesting the long-feared magnitude 9 Cascadia “Big One” could trigger a second major quake on California’s San Andreas Fault, creating a devastating chain reaction that would hammer much of the Pacific coast.The startling discovery, published in Geosphere, is based on thousands of years of underwater sediment that appears to show both fault systems ruptured close together in the past.“It’s kind of hard to exaggerate what a M9 earthquake would be like in the Pacific Northwest,” said Dr.Chris Goldfinger, a paleoseismologist at Oregon State University, in a statement to the Geological Society of America.

“And so the possibility that a San Andreas earthquake would follow, it’s movie territory.”A magnitude 9 Cascadia earthquake would already rank among the most destructive natural disasters imaginable, unleashing violent shaking, massive tsunamis and landslides across the Pacific Northwest.The new findings suggest California may not have much time to recover before another major disaster strikes.Ironically, the discovery happened because of a mistake.During a 1999 research expedition, scientists were collecting seafloor sediment to reconstruct Cascadia’s earthquake history when a graduate student accidentally entered the wrong latitude, sending the research vessel about 90 kilometers south into an area influenced by the San Andreas Fault.“We wound up off northern California,” Goldfinger recalled.“When I woke up, I was pretty hot.

But, once we were there, I thought, ‘well, let’s take a core here.'”The wrong turn revealed something researchers never expected.A sediment core collected from Noyo Canyon near Fort Bragg contained repeated pairs of deposits left behind by underwater landslides instead of the single layers scientists normally see.The same unusual pattern also appeared in samples collected from Cascadia.“There we...