How likely will the ‘big one’ occur in our lifetime?

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How likely will the ‘big one’ occur in our lifetime?

Editor's Note: This story first appeared July 16, 2015 and answers questions inspired by an article written by The New Yorker's Kathryn Schulz. Her story, "The Really Big One," was awarded the Pulitzer Prize for Feature Writing on Monday. The Pulitzer Prize is considered journalism's highest honor.

Some in the Northwest have admitted to losing sleep after the New Yorker's terrifying article on how the "big one" will devastate Seattle and everything west of Interstate 5. 

"If the entire [Cascade Subduction] zone gives way at once, an event that seismologists call a full-margin rupture, the magnitude will be somewhere between 8.7 and 9.2," wrote Kathyrn Schulz. "That’s the very big one."

People are calling into the Seattle Emergency Management Office asking what they can do -- and if Seattle is prepared. 

Debbie Goetz with the department said the city is prepared for the "big one."

She says the best advice for people living here is to have an emergency plan: Discuss with your family where and how you'd meet up in the event of an emergency that knocks out cellphone service.

Local experts -- from Pacific Northwest Seismic Network, Seattle Emergency Management Office, and The Seattle Times -- weighed in on the Cascadia earthquake during an Ask Me Anything on Reddit

John Vidale, director of the PNSN, wrote in the AMA, “ Overall, it was a well-written and documented article. The scenario left an impression of much greater devastation that is anticipated to occur, however."

As the science in Schulz's article is correct, below are seven questions and answers that may bring a little calm. 

1. You say the average frequency of such an event is 1 in 300 years. Do you know if the distribution is roughly uniform? My guess is that it would tend to decrease over time -- but I've also just googled and found articles that suggest continental drift is actually speeding up. Or is the distribution of big earthquakes something that we don't really have a good handle on at the moment? 

Good question. At the highest magnitude, the magnitude-frequency distribution is no longer exponential. The Gutenberg-Richter distribution is recast as the truncated or doubly-truncated Gutenberg Richter distribution, which reflects approaching a physical limit on the possible size of earthquakes.

I think the global limit is thought to be somewhere around 10. But remember, breakage of Cascadia has a small chance of triggering the Queen Charlotte fault, which has a small chance of triggering big faults along the Aleutians. So in the case of very, very, very rare and large events, one is not limited to just one fault.

2. Will Seattle (or anywhere in the PNW, really) ever implement earthquake early warning systems as mentioned in the New Yorker article about Japan?

We [PNSN] are currently testing earthquake early warning in the Pacific Northwest, in fact I have it on my phone now.

It needs more testing and full funding before it is ready to be released to the public, however. 

3. How would a major earthquake affect the nearby volcanoes? 

The same process of subduction - where one tectonic plate dives under another - is responsible for both our earthquake risk and the creation of our volcanoes. In other places, like Chile, volcanic eruptions have followed major earthquakes. Several of Japan's volcanoes became more active after their M 9 quake and tsunami in 2011. But I haven't heard of any good evidence that Mount Rainier or other Cascade volcanoes erupted in a serious way in 1700, the year of our last megaquake. 

4. Any chance of a NW quake setting off the Yellowstone caldera? 

Zero. And a Yellowstone eruption is so unlikely and so prevalent among questions from the public that it is a major source of irritation to many scientists. 

5. Did you see inaccuracies in the New Yorker article or was there anything about it that bothered you? 

Overall, it was a well-written and documented article. The scenario left an impression of much greater devastation that is anticipated to occur, however. 

6. What are the chances "the big one" will never come in our lifetime? How much do most of us not understand about probability and statistics when it comes to natural disasters like earthquakes?

If the chance it will come is 15%, the chance it won't come is 85% (if we're expecting to live another 50 years). However, there are plenty of "pretty big ones" to worry about as well, so you're overwhelming likely to see some action in the PNW.

Statistically, we're more likely to have another deep source quake like the Nisqually, that occurred in 2001. Chances for another one are above 80% within the next 50 years.

7. How realistic is it that 3 days' supplies (the minimum recommended) will enable my survival of the Very Big One in Seattle? And how many days' supplies do you personally have in your home ready for an earthquake?

We recommend people prepare themselves for 7 to 10 days vs. three. For a major quake, life won't be back to "normal" after just three days. I've got enough at home to make it through a week, and also keep a stash of stuff in my car as well as at work.

Beyond supplies, I always encourage people to talk about their plans - especially around communication, which we know will be affected. Where will they be? How can they get back together? Where could they meet if not at home? 

(Getty file photo OLIVIER MORIN/AFP/Getty Images) OLIVIER MORIN/AFP/Getty Images
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