Our Northwest

Tiny, deep tremors could trigger megaquake

Tuesday, April 28, 2015by  Jon Osterberg

Scientists recently concluded that tiny “slow slip” tremors in the Cascadia Subduction Zone can boost the risk of a Northwest megaquake.
     Twenty miles underground, weak, slippery rock is stressed by the fluctuations of tidal forces. New insight suggests that the resulting slow slip tremors add pressure to the shallower layer of tectonic plates. When the shallow layer ruptures, it can trigger a huge earthquake up to magnitude 9.0, as happened here 315 years ago.
     The Seattle Times reported news of these findings as Nepal reels from a magnitude 7.8 quake, almost 50 years to the day after Seattle’s 6.5 shaker of April 1965.
     I was standing in our living room at home, about to walk to my 5th-grade class, when that 1965 tremor hit. I was more fascinated than scared, never having been in an earthquake. But my poor mom went nuts. She had grown up in Los Angeles and endured several fearful tremors in her youth.
     Scientists surmise that slow slip might increase before a Cascadia megaquake, and if so, they could issue warnings that might buy the public time to prepare.

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