PBS Terra explains 'How Scientists Solved the Mystery of a 300-Year-Old Megaquake'

I closed PBS Terra explains 'The AMOC Might Be WAY More Unstable Than We Thought...Here's Why' with a preview of coming attractions.

I'm not the only one recycling a subject; PBS Terra's previous video is the latest in a series that began with PBS examines the risks from a major earthquake in the Pacific Northwest and continued with PBS Terra explains 'Here's EXACTLY What to Do When the Next Megaquake Hits: Cascadia Subduction Zone' and PBS Terra asks 'What's the ONE THING You Can Do To Survive a Tsunami?' I will almost certainly cover that in a future entry...Stay tuned.

Without any further ado, here is that video from PBS Terra explaining How Scientists Solved the Mystery of a 300-Year-Old Megaquake.

The 1700 Cascadia earthquake and tsunami was a massive natural disaster that reshaped the Pacific Northwest. Through tree rings, soil layers, and international collaboration, scientists have pieced together the exact timing of the event. As the region braces for another quake, can we prepare in time? Find out how new models and tsunami evacuation towers are helping coastal communities face the threat.

This video shows that it took the efforts of people in multiple disciplines, geology, biology, and history, to decipher the evidence and connect it all together into a coherent reconstruction of the event in 1700. It also shows, like the previous episodes, how people are preparing for the next event. One of those preparations are escape towers. As I wrote last year, "my first instinct if I can't get away from the shore would be to climb up, so I'm relieved to see people building vertical escape structures. Now to build more than three in the U.S." If they're all as well-stocked as the Shoalwater Tribe's, then the people should be in good shape to survive the tsunami.

Follow over the jump for the comments from last year's post.

Infidel753's comment and my response formed the bulk of the reaction to the video a year ago, so I'm repeating that today, beginning with Infidel's remark.

This is an important reminder of a major danger. However, I question the emphasis on the tsunami as opposed to the earthquake itself. The coasts of Oregon and Washington are lightly populated. The major cities like Portland and Seattle are a hundred miles inland -- even if the tsunami traveled up the river estuaries as the video says, only the parts of the cities near the riverbank would be affected by that. I would expect structural collapses in those cities from the ground shaking itself to kill a lot more people than the tsunami wiping out the coastal towns.

I supported then refuted Infidel's points in my response.

On the one hand, the Future Threats section of the Wikipedia article on the 1700 Cascadia Earthquake supports you: "[T]he major nearby cities, notably Seattle, Portland, Vancouver, Victoria, and Tacoma, which are located on inland waterways rather than on the coast, would be sheltered from the full brunt of a tsunami. These cities do have many vulnerable structures, especially bridges and unreinforced brick buildings; consequently, most of the damage to the cities would probably be from the earthquake itself." So you're right there.

On the other hand, the coasts of Oregon and Washington may be lightly populated compared to the Willamette Valley and Puget Sound, but the Oregon coast still contains about 100,000 people. According to the Census, Curry County has three cities on the coast, Brookings with 6,744 people, Gold Beach 2,241, and Port Orford 1,133. Coos County has Coos Bay with 15,985, North Bend 9,695, Bandon with 3,321, and Lakeside 1,699. Most of Douglas County and Land County lie inland, but the former includes Reedsport with 4,310, Winchester Bay with 382, and Gardiner with 248, and the latter includes Florence with 9,553, Heceta Beach with 1,912, and Dunes City with 1,303, all of which are on the coast. Lincoln County stretches along the coast with Newport at 10,853, Lincoln City with 9,815, Lincoln Beach with 2,045, Waldport with 2,033, Depoe Bay with 1,398, and Yachats with 994. I've been to Tillamook County twice, which includes Tillamook at 5,231, Rockaway Beach at 1,312, Pacific City with 1,109, Garibaldi with 830, Netarts with 744, Manzanita with 603, Oceanside with 361, and Nehalem with 355. Finally, Clatsop County includes Astoria with 10,181 (on the Columbia, but still likely to get hit by a tsunami; the same would be true of Knappa with 1,007 and Svensen with 853), Seaside with 6,457, Warrenton with 6,277, Gearhart with 1,793, Cannon Beach 1,489, and Jeffers Garden with 368. Those add up.

Besides, the tsunami will be felt a long way away. Scientists got the date of the 1700 earthquake from records in Japan. Conversely, the tsunami caused by the 2011 quake near Fukushima caused millions of dollars of damage along the U.S. coast. Don't discount that!

That was quite the rabbit hole to fall down! As for the populations of the towns along the Oregon coast adding up, they do, to 124,634. "About 100,000 people" turned out to be a conservative estimate.

Infidel raised the likelihood of an earthquake in his comment to PBS Terra asks 'Is This Type of Fire IMPOSSIBLE to Stop?'

Here in Oregon we've had several very bad wildfires in the last few years, with entire small towns destroyed. I'm beginning to wonder whether moving out of Portland to a smaller place would actually be a good idea. I've seen estimates of a 15% chance that a subduction-zone quake (which would destroy Portland) happening in the next fifty years, but wildfires happen every year, and a major city like this would at least be better defended against those.

I agreed with him about the relative risks.

You would have to move quite a ways inland to escape the effects of a magnitude 9 earthquake. Bend may not be fat [far-sic] enough. But you would definitely be safer from wildfire in a large city. Bend might just be large enough. Lahaina certainly wasn't.

I caught my mistake a bit too late, so I corrected it in my next comment: "Far, not fat. Now I'm wondering if I accidentally revealed a truth making that mistake." I still do.

I expect the late-night talk show hosts will return from holiday break tonight, so stay tuned for their monologues tomorrow. Who knows, they might have something darkly funny to say about the anniversary of January 6th worth sharing.