13 July 2015

Cascadia Tsunami ~ Understanding Tectonic Risk

Kathryn Schulz writes in The New Yorker of The Really Big One...
"An earthquake will destroy a sizable portion of the coastal Northwest. The question is when. [...] At approximately nine o’ clock at night on January 26, 1700, a magnitude-9.0 earthquake struck the Pacific Northwest, causing sudden land subsidence, drowning coastal forests, and, out in the ocean, lifting up a wave half the length of a continent. It took roughly fifteen minutes for the Eastern half of that wave to strike the Northwest coast. It took ten hours for the other half to cross the ocean. [...] We now know that the Pacific Northwest has experienced forty-one subduction-zone earthquakes in the past ten thousand years. If you divide ten thousand by forty-one, you get two hundred and forty-three, which is Cascadia’s recurrence interval: the average amount of time that elapses between earthquakes. That timespan is dangerous both because it is too long -- long enough for us to unwittingly build an entire civilization on top of our continent’s worst fault line -- and because it is not long enough. Counting from the earthquake of 1700, we are now three hundred and fifteen years into a two-hundred-and-forty-three-year cycle."
Here's a simulation of what happened back in 1700... And here's a geologist's discussion... Finally, documentary shock & awe imagery... NYTimes' DotEarthling Andrew Revkin weighs in too, with nice infographic showing past 8.0 and 9.0 events over 10K years... http://dotearth.blogs.nytimes.com/2015/07/13/a-chilling-update-on-the-ticking-seismic-bomb-off-the-u-s-northwest-coast/?_r=0

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