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Seattle, suburbs would lose all water pressure after earthquake, study says

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As Anchorage recovers from Friday's 7.0 earthquake, some in Seattle may be wondering what an equivalent earthquake — or worse — would look like here. Which makes a new study by the Seattle Public Utilities all the more timely.

The study says a disaster that was on par with the 2011 quakes in Tohoku, Japan and Christchurch, New Zealand would cripple SPU's regional system.

SPU, which provides drinking water to 1.4 million people, says that Seattle would lose all water pressure within 24 hours of the quake between 7.0 and 9.0 magnitude, and would need at least two months to return all of the water service to the city. To restore "pre-earthquake reliability and service levels to SPU's water system," it would likely take years.

It wouldn't be just Seattle, either: SPU's customers in Bothell, Woodinville, Redmond, Bellevueand more would also lose service.

SPU paid five consultants $900,000 for the 772-page, three-year long study. The only information that the utility service is issuing to the public, however, is a 13-page executive summary.

The summary details what would happen if an earthquake between 7.0 and 9.0 magnitude hit on the offshore Cascadia Subduction Zone. According to the study, between 1,400-2,000 pipeline breaks are likely, resulting in the loss of tap water for showering, flushing, firefighting and drinking.

Though repairs to smaller distribution pipes on the system could start almost immediately, it could be as long as eight weeks before SPU could start repairs on the transmission pipes at underground locations and steep slopes.

That analysis didn't even get into what would happen to the distribution pipes to the suburbs, or the sewer system under Seattle (which is operated only partly by SPU, and partly by King County).

And -- as many Pacific Northwesterners know all too well -- a big earthquake has long been forecasted for the area. According to the study, Seattle faces a 15 to 20 percent chance of a severe earthquake in the next 50 years.

Additionally, the study states that there's an approximately 84 percent chance there will be another earthquake similar to the 6.8 magnitude Nisqually quake.

In recent decades, SPU has spent millions to upgrade pump stations, pipelines, underground resevoirs and more in the case of an earthquake. But according to the analysis, the city still has a long way to go to properly protect the water system.

They determined upgrades are needed in a number of locations, including transmission pipes that cross under the Ceder, Duwamish and Green rivers.

Though the study advises specific pipe styles to help prevent breaks in an earthquake, they cost twice as much as regular pipes and are more extensive to install. According to a proposed project schedule in the study, SPU could spend $10 million to stockpile materials for repairs by 2023. From then on, it would cost about $15 to $20 million per year, with an early focus on at-risk locations like Alki, Interbay, South Park, Rainier Valley and more.

For now, the utility is committed to a plan approved by the city council last year, to be updated in 2020.

That's not the only way that Seattle would be affected in an earthquake, of course. Click through the slideshow above to see how the city would hurt Seattle.

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