UPDATE: New tsunami video released today (stunning video released yesterday has been removed from YouTube by the uploader): http://tinyurl.com/5s7lqe7
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PORT TOWNSEND — When Brian Atwater gave a presentation about the North Olympic Peninsula’s tsunami hazards March 10, about a dozen people showed up to hear him in Port Angeles.
That was hours before the magnitude 9.0 earthquake and resultant tsunami rocked northeast Japan.
A lot has changed.
No doubt motivated by pictures of quake and tsunami damage from Japan as well as tsunami damage to marinas in California, a standing-room-only crowd of about 275 people packed into the USO building at Fort Worden State Park on Sunday to hear Atwater, a U.S. Geological Survey geologist and noted tsunami expert.
Also speaking was Ron Tognazzini, a retired civil, structural and earthquake engineer from Sequim.
Both discussed the regional hazards from tsunamis.
“It’s in everybody’s mind,” said event organizer and paleo-seismologist Michael Machette, a member of the Port Townsend Marine Science Center’s Quimper Geo Group, which sponsored the forum.
Atwater showed computer models depicting plate movements in the subduction zone off the northeast coast of Japan earlier this month.
He said the plate boundary that caused the disaster in Japan is similar to the Cascadia Subduction Zone, a plate boundary about 75 miles off the coast of British Columbia, Washington, Oregon and Northern California.
Earthquakes in the Cascadia Subduction Zone cause tsunamis on an average of once every 500 years.
“There’s a long history of repetition,” Atwater said.
“It’s not like clockwork. It can’t be a regular impulse. We can’t tell you whether it will be tomorrow or centuries from now.”
The last big Cascadia Subduction Zone earthquake happened on the evening of Jan. 26, 1700, said Atwater, who matched evidence he found in tidal flats with written accounts of the tsunami in Japan.
When the next “big one” hits, Neah Bay residents will have about a half-hour to get to higher ground, preferable 50 feet above sea level.
Port Angeles residents will have about 90 minutes before the first wave hits, and Port Townsend residents will have two hours or more.
However, a localized tsunami caused by an earthquake along the Whidbey Island fault would give Port Townsend residents much less time — perhaps a half-hour — to get to a safe place.
Atwater and Tognazzini said people living in low lying areas along the eastern Strait of Juan de Fuca need to be prepared for both kinds of tsunamis.
“We just don’t know, in the history of nine tsunamis that were recorded out of Discovery Bay, which if any of them can be blamed on a nearby fault,” Atwater said.
“It’s possible they’re all Cascadia. We’re not sure.”
Tognazzini presented the research of Marley Iredale, a former Sequim High School student who sampled mud in the tidal flats of Discovery Bay in 2008 and 2009 for her award-winning study, “Evaluating Tsunami Risk in Discovery Bay, Wash.”
Iredale found that tsunamis have hit Discovery Bay at an average rate of once every 242 years — about twice as often as tsunamis formed from a temblor in the subduction zone.
“This project is probably the best project that we have seen come out of the Peninsula are in a very, very long time,” said Tognazzini, a retired civil, structural and earthquake engineer.
Tognazzini, who mentored Iredale, presented the findings because Iredale is away at Washington State University in Pullman.
A localized tsunami in the Strait of Juan de Fuca could be triggered by landslides, both underwater and above ground, from earthquakes along one of three Whidbey Island faults or the Seattle fault, Tognazzini said.
Local tsunamis tend to have a lot of energy concentrated in a small area and could trigger a tsunami just as big or bigger than one formed in the subduction zone, he said.
Discovery Bay is particularly susceptible because of its geography and low-lying south end.
“Fat Smitty’s [the restaurant] would no longer be there, but more importantly (U.S.) Highway 101 would be gone,” Tognazzini said.
“That small bridge on Highway 101 beside Fat Smitty’s would be probably destroyed by a local tsunami.”
It isn’t clear what caused the nine known tsunamis in Discovery Bay over the past 2,100 years, he said.
The Jefferson County Emergency Management agency had a booth at Sunday’s event during staff distributed fliers showing tsunami hazard zones in Port Townsend and evacuation routes.
State Department of Natural Resources tsunami evacuation route maps are available online at www.tiny.cc/a94k9.
The maps are tailored to individual communities and include evacuation routes for LaPush, Neah Bay, Clallam Bay, Port Angeles, Sequim and Port Townsend.
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Reporter Rob Ollikainen can be reached at 360-417-3537 or at rob.ollikainen@peninsuladailynews.com.
