Friday's earthquake in Alaska, and the 2001 Nisqually quake in Puget Sound, were significant. But neither was the big one.
Scientists put our chances of a mega-quake, like the one in Japan in 2011, at 15 to 20 percent in the next half-century.
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If that happens, a new report for Seattle Public Utilities, first reported by The Seattle Times, shows water pressure for the city and much of the Eastside could be lost very quickly, within 16 to 24 hours.
"Water and wastewater systems are some of the most vulnerable to earthquakes," said Scott Miles, a senior research scientist at the University of Washington who studies restoration and recovery from disasters.
Miles said the city's study appears to be impressive, but he's just been able to read the executive summary.
The city has only released 16 of some 700 pages.
"I am disappointed that they didn't release more of the report," Miles said.
Miles said it's important elected leaders in particular understand the risk so they can fund a fix.
Alex Chen, who directs drinking water planning for Seattle Public Utilities, says federal Homeland Security officials limited what could be released, and the city is now talking with them about making more information public.
"The public has a right to know what can be shared with them without compromising the security of the water system," Chen said.
The report estimates seismic improvements over the next 15 to 20 years could cost $40 million to $50 million.
Longer-term work over the next 50 years would cost more than $800 million.
Chen said SPU has already spent $100 million making the system more seismically robust.
Because of the report, the utility has decided to keep open a reservoir in the Roosevelt neighborhood and another in Volunteer Park for emergency backup.
"They will remain disconnected but we will be able to connect them in a hurry after a major catastrophic earthquake," Chen said.
Emergency management officials said the big takeaway from the report is for everyone to prepare their own backup water supply.
They recommend storing one gallon of water per person per day, for two weeks.
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