Sandi Doughton, science writer for The Seattle Times, specializes in explaining difficult subjects. Sometimes difficult also means “scary,” as in mega-earthquakes that hit magnitude 9.0.
Such a quake struck the coast of Japan in 2011, followed by a tsunami that swamped the coastline, killed thousands and caused the meltdown of a nuclear reactor.
The Northwest has felt such quakes as well, though not in living memory. The last big one dates to 1700. The region’s geology is “shot through” with shallow faults, she says. Those create one kind of quake, but the bigger shakes will start off the coastline on the ocean floor, where colliding tectonic plates push against each other. When the tension becomes too great, megaquakes result.
In her first book, “Full Rip 9.0,” Doughton, a former News Tribune reporter, discusses the science behind those quakes, the research that led to the discovery of earlier quakes in the region, and the likelihood that another mega-quake will rock the Northwest in the future.
Question: What made you want to write a book about this subject?
Answer: It’s one of those things where the understanding of earthquakes in the Pacific Northwest has changed dramatically in the past 25 years or so. I thought it would be a good time to look back and pull together all that new understanding.
Q: And what is new?
A: Thirty years ago, people had no idea that the Pacific Northwest is potentially subject to the most powerful earthquakes and tsunamis in the world. The only thing people knew is that we’d occasionally get these shallow quakes.
Q: Your book cites the recent revelation that this region experienced a mega-quake in the year 1700 — what’s the story behind that?
A: It’s an amazing geologic detective story. This one particular scientist, Brian Atwater (a professor at the University of Washington) discovered, in a way, that there had been this major quake in 1700. Of course, that was before any white settlers were here. The Native Americans experienced it – there were stories of a big earthquake and the ocean rushing in – but none of those were written down. The discovery, or rediscovery, that we had had a quake like this was quite an accomplishment.
Q: How did he figure that out?
A: The interesting thing is he wasn’t an earthquake expert. He was this guy who studied mud. But from that, interpreting different layers of mud what Brian found was a succession of these layers – evidence for at least 19 of these giant quakes in the last 10,000 years and possibly more. The most recent one was the one everyone was most interested in – somewhere between 1600 and 1700. Eventually, they pinned it down to the exact date and time based on records in Japan.
Q: Wow – how was that done?
A: An earthquake in 1700 would have caused a tsunami that would have hit Japan. They’ve been keeping records and writing about earthquakes for a thousand years – a very literate society. Records from several coastal communities talked about strange flooding in the middle of night in January of 1700 – like a tsunami, but nobody had felt an earthquake. A Japanese scientist with computer modeling simulated how long it would have taken for waves to cross the Pacific. And they came up with Jan. 26, 1700, at 9 p.m.
Q: So 19 big quakes in the last 10,000 years, or more?
A: The evidence comes from the sea floor. These big quakes shake loose layers of sediment that have gathered for centuries. The sediment barrels down slopes toward the sea floor. These things have laid down a succession of layers, which suggests 19 really big quakes, 9.0 or bigger.
Q: Have theses quakes come at regular intervals?
A: No, but there’s an average: 200 to 800 or 900 years. “Full Rip 9.0,” what that means is an earthquake that rips the entire subduction zone – when that happens the quake is going to be at least magnitude 9.0.
Q: So we’re overdue?
A: “Overdue” is a term that applies to babies, not earthquakes. The intervals between them are so irregular. You can’t bank on them occurring on a regular schedule.
Q: What draws you to these subjects?
A: Seismology is a very interesting branch of science. It’s kind of at the intersection between science and society. You can see the research having a clear impact. You can see how the field work of geologists has led to this new understanding, and you can see how that’s beginning to sink in.
Q: What’s under the surface in Tacoma?
A: The Tacoma Fault. There are shallow faults that run from the Oregon border up to the Canadian border. They’re particularly prominent in Washington. Washington’s being squeezed from north and south, so these faults have formed. The Tacoma Fault runs across Hood Canal, kind of through Tacoma over toward Auburn. There’s evidence that it is part of this fault complex that went off about 1,100 years ago, about 930 A.D. The bottom line is that there is an active fault that runs from Hood Canal under Tacoma that has generated powerful earthquakes in the past and probably will do so again in the future.
Q: What can we learn from this stuff?
A: A lot of people think this is something that’s too scary to think about. But the way I see it is we’re really lucky – that a generation of geologists have devoted their careers to putting together this puzzle.
Q: What’s important for us to know as a region, since we’re susceptible to these big quakes?
A: The real issue for the Northwest is kind of our regional infrastructure. That’s the thing as a society that we need to pay more attention to. These kinds of subduction-zone quakes or megaquakes are particularly dangerous for tall buildings. More than half of the tall buildings in Seattle, Tacoma, Portland and Vancouver were built before 1990. And we have thousands of old brick buildings that haven’t been retrofitted. We also have thousands of old concrete buildings that could pancake in a major earthquake, and nobody’s looking at those.
Q: What else?
Beyond that – the bigger thing is our utility infrastructure. In the Kent Valley, which is low-lying, when the ground shakes it’s going to turn to jelly. It could be over a year before people get sewer and water service restored. Power could be out for weeks and months. We need to start strengthening that infrastructure.
Q: Do you drive the Alaskan Way Viaduct?
A: I live in West Seattle, so I drive it northbound, then I come home on the freeway, mostly because of traffic. It’s a gamble.
Q: You said California’s quakes are shallow – different from the deep quakes we might experience in the Northwest – but many of us remember the Bay Area quake of 1989, when freeway ramps and other structures collapsed. Would we see greater damage around here in the event of a big quake?
A: In a megaquake on the coast, we’ll see a lot of bridges go down. The Puyallup River Bridge is one of the top concerns in the state. We’ll see dozens and dozens of freeway bridges go down. The coast will be completely cut off from the rest of the region, then the tsunami will come. It will completely overrun low-lying communities like Ocean Shores, Long Beach, places like that. FEMA estimates the damages would be about $80 billion.
Q: You know all this stuff as well as anyone – how do you prepare personally?
A: I’ve sort of taken to heart the advice about having an earthquake kit at home, in my car and at work. I’ve got food – power bars – water, flashlights, batteries. Things like that are going to be essential to survival. I’ve even got one of those little hand-crank radios.