Expect the Unexpected: More 9.0 Megaquakes Are Coming, Study Says [View all]

[bananas]

Source: NBC

No one should be surprised if a magnitude-9 megaquake erupts off America's West Coast — or anywhere else around the Pacific Ocean's "Ring of Fire," for that matter.

That's the upshot of a study in October's issue of the Bulletin of the Seismological Society of America: Researchers say that computer models of future seismic activity, plus a check of past activity going back thousand of years, suggest most of the Pacific's earthquake zones are capable of generating shocks at least as strong as magnitude 9 every 10,000 years on average.

Seismologists were surprised in 2004 when a magnitude-9.3 quake and tsunami devastated Sumatra and caused more than 200,000 deaths around the Pacific Rim. They were surprised again in 2011 by Japan's 9.0 quake and tsunami, which killed more 15,000 people and touched off a nuclear catastrophe that continues to this day.

In each case, experts didn't think the area where one geological plate is diving beneath another — known as a subduction zone — was capable of generating a quake that strong.

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In addition to coming up with the 10,000-year figure for the probability of 9.0 quakes, they estimated that quakes of at least magnitude 8.5 should be expected at least every 250 years, and 8.8 quakes should be expected every 500 years.

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Rong and her colleagues compared their figures with the sedimentary record for the Cascadia zone, and came up with estimates that were somewhat different for that area. They said that 9.0 quakes should be expected every 1,000 years for Cascadia, with 9.3 quakes over a 10,000-year period.

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Read more: http://www.nbcnews.com/science/environment/expect-unexpected-more-9-0-megaquakes-are-coming-study-says-n203936

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Note that those probabilities are per subduction zone, and there are multiple subductions zones, so the total frequency is much higher.