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Seaside city councilor questions earthquake and tsunami model

Horning wants other factors considered
By Brenna Visser

The Daily Astorian

Published on June 13, 2018 8:10AM

An Oregon State University computer model flagged several bridges and roads in Seaside that could pose problems in an earthquake and tsunami.

Colin Murphey/The Daily Astorian

An Oregon State University computer model flagged several bridges and roads in Seaside that could pose problems in an earthquake and tsunami.

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SEASIDE — Seaside City Councilor Tom Horning said the city should consider more than just a computer simulation released earlier this week by Oregon State University when it looks at bridge replacement.

The model found certain bridges and roads in Seaside will have higher mortality rates in an earthquake and tsunami.

“I think the OSU modelers have done a nice job with their models, but their conclusions need to be considered along with other issues,” Horning, a geologist, said. “I think they are valuing the population densities too aggressively.”

Researchers found the bridge on Broadway Street over Neawanna Creek would result in the most fatalities and should be prioritized for improvement. Other critical locations are the two bridges on 12th Street, the bridge on Sundquist Road and Ocean Vista Drive in the Cove.

These bridges and roads were identified as high priorities to retrofit not because of structural integrity issues or age, but because of relative proximity to areas where people live and gather. They also fall in the path where tsunami inundation will most likely occur, researchers said. The simulation ran thousands of scenarios based on the starting points of 4,500 imaginary people, who were distributed mostly downtown and on the beach to resemble where most people would be on a busy, summer day.

While Horning agrees the Broadway Bridge and 12th Avenue structures are heavily trafficked, these bridges happen to be ones that will fare “quite nicely” in the event of an earthquake, he believes, and that it is all the other bridges in town that could fail.

“I agree that the East Broadway and the 12th Avenue structures are important lifelines, but they ought to be regarded as capable of withstanding the next quake and they should be lauded as great examples of good bridges,” Horning said in an email.

Oregon State civil engineer Dan Cox said he did not want give the impression that the bridges were not good in this study since the team did not do any structural engineering analysis.

“The main focus of our study was to understand what were the most important bridges for evacuation,” Cox said.

In a July work session, Horning hopes to discuss a strategy and funding mechanism to replace all of Seaside’s bridges.

Last week, Cox and Wang emphasized their research — funded by the Oregon Sea Grant and the National Science Foundation — is not an end-all solution for tsunami preparations in Seaside, and that they hoped their findings would be a “piece of the puzzle.”

“This is not something to panic over,” Horning said. “It is something to participate in and complete within a responsible period of time.”



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