Cascadea subduction3/13/2023 ![]() The good news is that building codes are due to be strengthened nationwide. The M9 Project’s updated analysis, which takes account of longer-duration quakes as well as the Seattle area’s sedimentary basin amplification effect, would raise that projected risk to somewhere between 20% and 50% depending on building height and the standards followed for construction. … We’re hoping that our work will actually go to change that.”Įarlier analyses of earthquake effects pegged the risk of collapse for buildings up to 20 stories tall at less than 10%. “So we haven’t really incorporated long-duration effects in building codes that are in use in the U.S., because we haven’t really had long-duration earthquakes. “Our building code is all built on the California experience, because that’s where we’ve had a lot of earthquakes and a lot of building and infrastructure damage,” Berman said. That’s significantly longer than the duration of a typical California earthquake, and that adds to the bad news, said UW engineering professor Jeffrey Berman. ![]() The Cascadia subduction zone, centered along a submarine fault just off the West Coast, is known to be capable of generating magnitude-9 quakes, based on the geological and historical evidence for a massive tsunami that reached Japan in 1700.Īnd as if that weren’t bad enough, the Cascadia fault is so extended that the resulting quake is expected to last for about 100 seconds. The session - titled “Is the Coast Toast?” - followed up on a 2015 New Yorker article that painted a grim picture of the possibilities, based on studies of the Pacific Northwest’s Cascadia subduction zone. That’s the bottom line from a session focusing on Seattle’s seismic hazards, presented at ground zero today during the American Association for the Advancement of Science’s annual meeting. (NOAA / Pacific Tsunami Warning Center)Įarthquake experts say current building codes don’t reflect the riskiest features of the Seattle area’s geology - but the outlook for survivability looks a lot better if the Really Big One can just hold off for a few more years. Scientists believe such quakes occur every 500 years or so on average. A color-coded computer simulation from 2016 shows how researchers think tsunami waves propagated from a magnitude-9 Cascadia subduction zone earthquake in the year 1700.
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