By Jessica Wertheim
The Public Press
According to the U.S. Geological Survey, "there is a 70 percent probability that one or more damaging earthquakes of magnitude 6.7 or larger will strike the San Francisco Bay area during the next 30 years."
And San Francisco is taking no chances. The city’s newest project, headed by the San Francisco Public Utilities Commission, is the construction of a five-mile long tunnel located under the San Francisco Bay.
The tunnel, which will lie 103 feet beneath the floor of the Bay, would provide protection to the Bay Area’s water supplies if a major earthquake were to compromise other sources. "By building extra tunnels and strengthening our pipelines, it means we have much greater assurance that we’ll have water after the next earthquake," said Ed Harrington, general manager of the San Francisco Public Utilities Commission.
The tunnel also will be replacing "two large steel pipes built in 1925 and 1936 that sit on the floor of the bay." According to a recent article in the Oakland Tribune, these pipes could easily break in a major quake, which would effectively cut off water for weeks to many major cities.
By burying the tunnel deep into the earth, in "stronger, tighter materials, there is much smaller vulnerability to being pulled apart from shaking and liquefaction," said David Schwartz, a geologist with the U.S. Geological Survey in Menlo Park. "From an engineering point of view, it’s much stronger."
In addition to the construction of the tunnel, pipelines, water treatment plants and the Calaveras Dam also will be rebuilt over the projected timeline of five years. The retrofitting will result in the stabilization of the structures so each could "withstand a quake of up to magnitude 7.9 on the San Andreas fault and 6.9 on the Hayward fault."
The tunnel’s undertaking is scheduled to begin next spring with the projected completion date of 2015.