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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 theapparition on 5/25/2010 11:50:12 AM , Rating: 3
That gets right into the differences between "chance" and "probability".

If you flip a hypothetical coin 10 times and each time ends up heads, your probability that the next flip is tails is extreamly high. Your chance of tails however is still 50/50.

Probability considers the past outcomes and other factors, while chance completely ignores previous history.

Yellowstone caldera is also overdue for a super volcanic event. Probability is higher every day goes by; chance is the same as every day.

In the end, I guess it's only prudent to take proactive safety measures.


RE: Bias? Fishiness?
By Breathless on 5/25/2010 12:43:12 PM , Rating: 2
good point


RE: Bias? Fishiness?
By Solandri on 5/25/2010 12:52:40 PM , Rating: 3
No, probability and chance are the same thing. In your coin flip example, they're both 50% because the past events are independent from future events.

In an earthquake, past events affect future events. Lack of an earthquake allows stresses to build up, increasing the probability/chance of an earthquake. Having an earthquake releases the stresses, lowering the probability/chance of an earthquake.

I think you meant to say "average" and "probability" are different. The average is a low-pass filter run over multiple events, so gloms past and future events together to be evaluated as a single number even if they're independent. Probability keeps them independent. However, that's not really relevant in this case since past and future earthquakes are not independent.


RE: Bias? Fishiness?
By theapparition on 5/25/2010 9:19:07 PM , Rating: 2
They most certainly are not.

Probability factors in previous events to calculate the potential for future events, excatly what this article is about.

In the coin flip example, as you approach an infinite amount of tries, the probability approaches 50%. 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.

Suggest you read up on the actual differences between the two. It's not rocket science, just high school math. But look up Central Limit Theorem for more info.


RE: Bias? Fishiness?
By Solandri on 5/26/2010 4:25:45 AM , Rating: 3
quote:
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.

http://en.wikipedia.org/wiki/Gambler%27s_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.

e.g.
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.


RE: Bias? Fishiness?
By clovell on 5/26/2010 10:25:11 AM , Rating: 3
> They most certainly are not.

Yes, they most certainly are. Please pick up a textbook.

> Probability factors in previous events to calculate the potential for future events, excatly what this article is about.

No, probability doesn't do that. Bayesian inference, the inclusion of lag variables into a model, and autoregressive correlation structures all do that. However, it's not a default characteristic of probability.

> In the coin flip example, as you approach an infinite amount of tries, the probability approaches 50%. 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.

Okay, now you're just being an idiot. That is exactly what I said is NOT true. Each coin flip is independent of all the others. The probability of a coin flipping heads after 9 tails is 50%. So is the chance.

Now, the probability of flipping 9 tails then a head is pretty low, but that's because you're talking about TEN independent events (if anyone cares, the answer is (1/2)^10).

> Suggest you read up on the actual differences between the two. It's not rocket science, just high school math. But look up Central Limit Theorem for more info.

I've a Master of Science in Biostatistics, junior. I suggest you read a textbook on statistics rather than regurgitating the crap they dumb down for you in your intro courses.


RE: Bias? Fishiness?
By Iaiken on 5/25/2010 1:14:14 PM , Rating: 2
quote:
If you flip a hypothetical coin 10 times and each time ends up heads, your probability that the next flip is tails is extreamly high. Your chance of tails however is still 50/50.


Not entirely.

If you flip a coin 10 times and the previous 9 flips came up heads, your probability is the same as the previous 9 flips because the events are independent of each other. However, if you were you flip 10 coins simultaneously, the probability that all 10 come up heads is very low.


RE: Bias? Fishiness?
By Solandri on 5/26/2010 4:49:09 AM , Rating: 2
quote:
However, if you were you flip 10 coins simultaneously, the probability that all 10 come up heads is very low.

That's a subtly different problem. With the 9 coins flipped in sequence, the order matters. First you got 9 heads. Then you're asking what happens to the 10th flip.

If you flip 10 coins at once, then the order doesn't matter. You're saying any 9 of the 10 coins can be heads (rather than 9 specific pre-selected coins being heads). Then you're asking what's the chance of the 10th coin being heads.

Coin flip probabilities can get rather involved, especially with 10 flips. So the difference is best illustrated by a boy/girl example:
http://en.wikipedia.org/wiki/Boy_or_Girl_paradox


RE: Bias? Fishiness?
By atlmann10 on 5/25/2010 2:11:58 PM , Rating: 2
The Yellowstone addition to this discussion is the best point I have seen. Many do not realize that Yellowstone, or at the area underneath it is classified as a Super Volcano. If there is a major plate shift which opens it up I would not want to be living anywhere (within at least a 500 mile range) of it! A super volcano is a very, very bad thing.

So if there is a major tectonic plate shift in the area, which raises the probability of Yellowstone active behavior, then it could very well change the entire earth environment substantially. From evidence I have seen a mini ice age would most likely be the result. This is also not to mention the instant destruction range of at least a 500 mile circumference of Yellowstone.

While that is bad the ash and environmental disturbance caused by it would be even more substantial. Here is a link (http://exodus2006.com/supervol.html)to one study of it as well as many more related links. Basically if we have a major tectonic shift that affect's the area, and therefore causes this it will change the entire USA to a large extent. I will just say I live in Georgia, of which I am glad in respect to this. As Georgia would be out of the directly affected area.

However; active eruption of Yellowstone would change the world completely for quite some time (probably directly affecting at least a few thousand years), so let us all hope fervently that this does not happen. Although it is still an almost inevitable thing (as it is many thousand years overdue from what is known.


RE: Bias? Fishiness?
By clovell on 5/26/2010 10:39:47 AM , Rating: 2
> The Yellowstone addition to this discussion is the best point I have seen.

The discussion was about statistics and modelling. All you're saying is that if there's tectonic activity, the volcano will likely erupt. The discussion we're dealing with here is the premise of your arguement above. You're begging the question.

Nobody's denying that tectonic activity would do that. We're talking about whether expecting this level of tectonic activity is reasonable and warranted.


RE: Bias? Fishiness?
By clovell on 5/26/2010 10:34:21 AM , Rating: 2
> Probability considers the past outcomes and other factors, while chance completely ignores previous history.

Yellowstone caldera is also overdue for a super volcanic event. Probability is higher every day goes by; chance is the same as every day.


I've already addressed probability versus chance. Yellowstone caldera is only more at risk as time goes by if a significant cyclical trend has been observed. Realize that every day that goes by is informative in terms of history, and adds to the variance and uncertainty of a model.

Next time, try reading the post you're responding to.


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