Print 28 comment(s) - last by clovell.. on May 26 at 10:54 AM

This rendition of an OSU tsunami shelter prototype shows a large multi-story building on stilts, likely to lessen the impac of the base of a tidal wave crashing through its vicinity.  (Source: Oregon State University)
Shake, rattle, roll and splash -- major seismic event could ravage the pacific northwest twice over.

There have been no shortage of powerful and often, sometimes catastrophically, deadly earthquakes in the past ten years. Sumatra, Haiti, Japan, Chile and more have suffered to various degrees from the results of plate tectonics and the roiling seas of magma far below the surface of the planet. Though, in the US, California has a reputation for being earthquake-friendly, it is a far cry from the only threatened west coast state.

Based on data collected from the Cascadia Subduction Zone, which lies off the west cost of North America and runs from northern California up to British Columbia, Oregon State University marine geologist Chris Goldfinger and team says the chance of a quake of high magnitude, 8 or better, is unsettlingly high in the next fifty years. Using telltale signs of seismic activity, they have mapped out a time line of major events for the last 10,000 years. As it turns out, the pacific northwest is about due for a major earthquake.

According to their findings, the Cascadia has already gone past the 75% mark as far as a major event within a generally rhythmic period of time. Over the past 10,000 years, they have found evidence of 41 large events, spaced at roughly 500 year intervals. Should no event occur in the next 50 years, the chances jump to 85%. There is no doubt, feels Goldfinger, that the event is coming -- it's just a matter of time.

At present, he states there is an approximately 37% chance that a magnitude 8 or greater quake will hit the southern section of the Cascadia Subduction Zone, which runs from northern California to near Newport, Oregon, in the next 50 years. Further north, the chance of an event is less -- 10% to 15% -- but with a better chance of being much stronger, magnitude 9 or greater.

Not all of the west coast is oblivious to this sleeping giant. Not only would a sizable off-shore event cause the standard stand-in-a-doorway building rumbling action, it would most certainly create a powerful tsunami in its wake. The last recorded high magnitude quake from the Cascadia was in 1700. Though no records exist from the Americas, Japanese historians recorded the ocean-traversing tsunami that reached their shore, crashing down at 30 or more feet in height.

The town of Cannon Beach, Oregon, is working with engineers from OSU to create an earthquake and tsunami shelter for its residents using advanced construction techniques and an eye for vertical space to stand above the wave. If completed, it may be the first tsunami shelter built outside of Japan.

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RE: Bias? Fishiness?
By Solandri on 5/26/2010 4:25:45 AM , Rating: 3
But if a coin flip turned up heads 9 times, then you have a higher probability that the next try will come up tails. But your chance stays independant.

Either you are using incorrect terminology, or you are falling victim to the gambler's fallacy.

For independent events like coin flips (assuming a balanced coin), the probability for tails is always 50%. Doesn't matter if you got 9 heads or 9999 heads. The probability for tails was, is, and always will be 50%.

If you are talking about estimated probability, then the opposite of what you say is true. You take the average of the previous flips to work out a likelihood of coin being unequally weighted. For 9 heads, that works out to a 99.8% probability that the coin is two-headed. Thus your best estimate for the probability of the next flip being a head is 99.8%, with only a 0.2% probability of it coming up tails.

For dependent events like earthquakes, the probability increases the longer you go without an earthquake. But that's because of stress building up in the earth's crust. It has nothing to do with how probability works. Probability just allows you to statistically model the frequency of earthquakes, and based on that estimate the probability given how much stress has built up (how many years it's been since a big quake).

RE: Bias? Fishiness?
By Solandri on 5/26/2010 4:33:50 AM , Rating: 2
BTW, I'm pretty sure you're falling for the gambler's fallacy. The reason coin tosses trend towards 50% as you approach infinite tosses isn't because getting 9 heads means there's a higher chance for a tail. It's because the subsequent tosses will tend to be 50% and they swamp out the imbalance of the 9 heads by sheer sample size alone.

9 heads + 2 flips of 50% (1 head, 1 tail) yields 90.9% heads overall.
9 heads + 20 flips of 50% (10 heads, 10 tails) yields 65.5% heads overall
9 heads + 50 flips of 50% yields 57.6% heads overall
9 heads + 100 flips of 50% yields 54.1% heads overall
9 heads + 1000 flips of 50% yields 50.4% heads overall

See how it trends towards 50% even though the probability of a tail isn't greater than 50%?

RE: Bias? Fishiness?
By clovell on 5/26/2010 10:29:44 AM , Rating: 2
Right - that's where the Central Limit Theorem comes in.

So everybody is clear, the Central Limit Theorem doesn't describe the probability of a single coin flip. It describes how, as the number of flips approaches inifinity (gets bigger), the overall sample mean of those flips converges to within an epsilon neighborhood (keeps getting closer to) of the true mean/probability.

"And boy have we patented it!" -- Steve Jobs, Macworld 2007

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