The following video from the Washington State Department of Transportation (WSDOT), showing the effects of a 7.0 earthquake in Seattle is telling and is very much worth a watch. Even though Seattle’s Alaskan Way Viaduct is long past its prime and not designed for catastrophic earthquakes, it’s collapse plus the failure of other aged infrastructure is chilling.
The late transit expert, Des Turner, was always concerned about the effects of a large earthquake and on the mostly elevated Expo and Millennium light-metro lines. In theory, the SkyTrain viaducts should survive an earthquake measuring 6 on the Richter Scale with minimal damage, with few exceptions, such as if a support column fails due to local soil liquefaction or earth movement.
Unlike at-street/at-grade light rail, failure on any section of viaduct would mean several months of disrupted service on the metro until new columns and guide-ways could be rebuilt and emplaced. Large scale failure of the SkyTrain viaduct may even lead to line abandonment.
In summer 1995, a letter from a US engineer specializing in earthquake resistant design to Mr. Turner, expressed a worry that if a 7+ earthquake were to hit Vancouver, the elevated SkyTrain guide-way would fail in several sections, just like what happened in Kobe Japan in 1995, where once thought earthquake resistant viaduct design failed, with devastating consequences.
Vancouver doesn’t have 60 year old decaying elevated double-deck highway viaduct to worry about, but it does have a large elevated light-metro network, which some sections are now approaching some 30 years old and one wonders that TransLink has an earthquake plan, if and when the unthinkable happens.