Shakemap Scenario for a hypothetical M9 quake off of the Pacific Northwest
Wow, has the internet lost its everloving shit over this (very excellent) New Yorker article
As I read it, nodding along, reading things I'd read before, I figured it was just another addition to the already long bibliography of articles about Cascadia. When I was finished I put it aside after tweeting my thoughts.
Didn't realize it would actually terrify a great number of people, and that confused me. I wasn't alone. It confused the scientists too. More on that later.
For the last 20 years or so there's been a veritable cottage industry of getting the word out. I reviewed this book here in 2011. I finished this one last night and it was reviewed here by Lefty Coaster. There's also the synthesis that launched all of this, which you can download for free here (I don't know if you can buy it anywhere for a price that isn't psychotic. It appears to be out of print.)
And then there's books I've not yet read but recognize they're likely quite excellent. Like this one, and this one and this one.
Not to mention the periodic and frequent articles from local newspapers, reports from local media, and so on. Local scientists are incredibly visible too. Why the freaking out?
I think there's a miscommunication in how risk is perceived.
In Southern California, where the threat of a great earthquake is omnipresent, people there accept the risk with aplomb. When new faults under the LA Basin are discovered (and there are many, the basin is riddled with blind thrust faults), there's little overreaction from the public. This should surprise a lot of people, because a considerable bit of the public of Southern California is not native and was not there in 1994. You'd think they'd be freaking out. They aren't. They might not be getting prepared (as evidence, I can find video of people wondering how SoCal's recent minor quakes have trashed the interior of their homes but I see no evidence that they bothered to bolt anything down which is like living in Earthquake Country 101), but that's another story. There's only so much hand-holding government can do on preparedness matters.
Other areas of the country seem to be similar. I've never seen Utah residents lose it over the occasionally dire articles about the Wasatch Fault. The southeast and Gulf Coast accepts hurricanes, New England with blizzards. Oklahomans seem to have simply accepted their new earthquake hazard along with the tornadoes, the droughts, the occasional floods, and the occasional dust storms.
The Scientists Speak Out
The New Yorker piece had another flaw that I suspect is part of why everyone is terrified. This is the offending paragraph:
Thanks to that work, 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.
This actually gave me pause, since I'm up on the science, but like I said I initially put the article aside after I shared it. But the paragraph is not correct. Well, it is correct, but it's also not correct. I'll explain.
Actually, I won't be the only one to explain. Dr. John Vidale, Sandi Doughton, and Debbie Goetz will also.
Dr. Vidale runs the Pacific Northwest Seismic Network. Along with Sandi Doughton and Debbie Goetz of Seattle's Emergency Management Office they did aReddit "IMa" (I Am A) open house. They had to; what looked like panic was beginning to show up all over the place (exacerbated by an inaccurate Fox News report which I won't link).
It was very informative, I suggest everyone read through it, and this is probably the best subthread in the entire reddit thread, and here's another recounting of the best 5 things in that reddit thread. This Slate piece despite the subhead isn't bad either.
But back to the paragraph, it's correct. Hidden in the mud on the ocean floor is an impressive record. Using underwater landslides (underwater these are called turbidity currents) and the layers they leave in the muck on the seabed it's been determined there have been, over the last 10,000 years, at least 41 large earthquakes of magnitude 8 or higher. What the article left out and where it's not correct is only 18-19 earthquakes over the last 10,000 years were likely M9 or greater (up to M9.3) and ruptured the entire margin from California to Canada. About 23 were at least larger than M7.5 but were smaller than M9 and only occured on the southern margin from Newport, OR to Cape Mendocino, CA. A deep dig into the science shows anything lower than M7.5 will likely not cause a landslide large enough to make an impact on the geologic record on the ocean floor. The use of underwater landslides has turned many a skeptic into a believer of their use for building our knowledge of the past, including the scientist now championing them (Dr. Chris Goldfinger, interviewed in the article), and are being used all over the world where possible to assess the danger from very large earthquakes.
But the line "315 years into a 243 year cycle" is what is not correct. That applies from Central Oregon south to Cape Mendocino, and that earthquake will not be M9. From the USGS:
The combined stratigraphic correlations, hemipelagic analysis, and 14C framework suggest that the Cascadia margin has three rupture modes: (1) 19–20 full-length or nearly full length ruptures; (2) three or four ruptures comprising the southern 50–70 percent of the margin; and (3) 18–20 smaller southern-margin ruptures during the past 10 k.y., with the possibility of additional southern-margin events that are presently uncorrelated. The shorter rupture extents and thinner turbidites of the southern margin correspond well with spatial extents interpreted from the limited onshore paleoseismic record, supporting margin segmentation of southern Cascadia. The sequence of 41 events defines an average recurrence period for the southern Cascadia margin of ~240 years during the past 10 k.y.
Cascadia is segmented, like many if not all large fault systems, and each segment has its own behavior. The study of the underwater landslides, correlated with evidence from the sunken marshes along the coasts, and deposits on the floors of lakes, shows the southern segment is far more active than the northern segment. The Northern segment seems incapable of acting without the southern segment--meaning the M9s are less common than the statistic "315 years into a 243 year cycle" implies. But it also means M8s from about Newport, OR on south are a lot more common, based on the inferred record from the last 10,000 years. A "Full Rip", as Sandi Doughton calls it, may occur on average every 600 years (see the comments here
Do take the time to download what the USGS put together and read it. It's incredibly technical but you know what? You paid for it and I paid for it and every person living within the US's borders who pays taxes paid for it. It's literally a free post-secondary education. If anything, look at all the maps, graphs, and pictures within.
As to how science knows the sizes of these 41 quakes, well, they do and they don't. But they can make observations. The 1992 Cape Mendocino earthquakes were Cascadia quakes, but they do not seem to have caused underwater landslides. The 1906 San Francisco quake did off of Northern California, so its magnitude can be used as a useful proxy. The biggest quake of the 1992 sequence did thrust a portion of the California coast upwards by a few feet though. A good question being researched: how frequent are "smaller" quakes like the one at Cape Mendocino, and can they happen anywhere along the megathrust? Stay tuned.
It makes a for a far more compelling narrative (one I found important, because Kathryn Schultz highlighted some serious problems in Oregon and Washington, like OSU wanting to build in the inundation zone in Newport for example) to tell your audience that the great Really, Really Big One is over half a century overdue when it's not, not to mention seismologists kind of don't like the word "overdue" because the other thing about Cascadia is the quakes come in bunches separated by up to 1,000 years. The 1700 earthquake might be the end of an irregular cycle that's gone on for millenia for example.
The article also neglected to talk about big deep quakes. Several have occurred under Puget Sound, most recently in 2001. It isn't known how big one of these can be, or even if they can occur under Oregon too. There was a very deep quake just earlier this year near Japan that was an M8.
In addition it didn't discuss the shallow blind faults beneath Seattle and Portland (and Spokane, Olympia, Tacoma, and the Willamette Valley). An earthquake on the Seattle Fault around the year 900 caused tsunami on Puget Sound and broad regional uplifts. If it occurred today it'd likely kill far more Seattlelites than a Cascadia quake would. So much of the city is built on top of it. The good news about that is that quake in the year 900 seems to have been a one-time great event and there's little conclusive evidence that quakes (they think it was somewhere north of M7) that large have occurred frequently. The bad news is it's not the only threatening fault, not all faults have been researched across the region, and not even all faults are known, and that all the faults might have gone off in a long cascade triggered by a Cascadia quake around the year 900. The Puget Sound region seems as riddled with faults as the Los Angeles basin is. But the article was scary enough.
Easy. The bare minimum is 3 days, one should expect to be cut off in any given disaster. A better metric is 10 days people should expect to be on their own. From watching the news footage of disaster over the last 10 years, 3 days seems to be the standard minimum for anyone to begin to really respond in force.
Freaked-out people don't prepare, they run around with like chickens with their heads cut off. (That's a metaphor and an admittedly bad one drawn from the movies, I'm well aware of the research that strongly suggests that people don't panic in disasters at all. Here's a great link about that.)
But seriously, use your heads.
I enjoyed "Full Rip 9.0" because the author went out and interviewed people doing just that. That was one of the few flaws in the New Yorker piece, I thought. Ms. Schultz didn't interview anyone working on preparedness at all and it painted a narrative that there was nothing going on, something I know is not true. A homeowner's association in Seattle has regular classes on how to cheaply retrofit your house. One simple fix for homeowners: make sure your house is bolted to your foundation.
That's not to say Washington State and Oregon are close to being prepared. Where Washington State has building codes dating back to the early 1950s thanks to periodic large earthquakes in the historic record, Oregon did not have building codes because until the 1990s, there really weren't any quakes. Oregon is so far behind there's a very necessary parents' group demanding upgrades to schools. Schools all over Oregon are built like this one, near Salem, heavily damaged in a relatively minor quake in 1993.
We can look at this with hindsight and say "how could they be so dumb?"
I don't think that's fair. No one knew what was lurking offshore, and both states are rapidly catching up to where they need to be. You can start here for Washington State and here for Oregon.
In 2015 we really take for granted that seismology, as a science, is barely a century old and plate tectonics, as a science, is barely as old as I am. Neither state is California where earthquakes are so frequent. But they are getting ready. It would have been nice to see that in the New Yorker article.
It also would have been nice to see a mention of the early warning system currently in development on the West Coast. The article describes Japan's advanced system. Similar systems exist in Mexico City and the capital of Romania, and in Taiwan. I wrote about California's last year. There was no mention of the system being developed in California or the one in the Pacific Northwest at all. But again, the narrative was crafted to imply all was but hopeless. Such narratives disappoint me where I know progress is being made.
Like in the shore communities where the only warning will be the quake (and perhaps early warning depending on where the quake's hypocenter is, the further south, the longer leadtime for everyone on north). The tsunami will be ashore within minutes. There won't be time for people to wait. Grim, but many will be saved if they simply walk or even run for higher ground (the paper this is based on is here). And in other places where there is no high ground, shelters are planned or being built that conceivably would save people from drowning in the tsunami. Maybe not fast enough, but it's happening.
A big take away is all these efforts cost money. Identifying hazardous faults costs money (Sandi Doughton discusses this this in depth in her book). Resilience efforts cost money. Early warning systems cost money. A bigger take away is the article seems to have woken people up even as it made them lose their entire shit, people who really should have known better. Media is using this as a teachable moment. Perhaps that's why the narrative was written the way it was. I've known about this for years and still would decamp for the Pacific Northwest if a job opportunity came along but maybe there's a bunch of new transplants who haven't a clue. Bet they do now.
1. Earthquakes can't be predicted, at all, so if you come across someone on the internet who says otherwise they're either a quack, a liar, or both. That's not to say there aren't real scientific efforts to get there, but I don't think they will ever get there. (The linked PDF is just one of many out there. I won't link to the quacks although I'm sure some of y'all are well aware of them and probably think they even have merit. They don't. Not a one.)
2. This is a great site and a great organization. There's so much good stuff on that site. If you're freaking out or if someone you know is, send them to CREW.
3. Oregon State has been kind enough to make a great deal of its data, if not all of it, available for everyone to read.
No excuses now. If you live in a place with hazards, you should know them and know how to respond to them, and not freak out.