Portland On Shaky Ground


A reader builds off our Seattle post:

I was in architecture school in Oregon (M.Arch, University of Oregon, Eugene)  in the mid-1990s, not long after the SF Loma Prieta quake and at the time of the LA Northridge quake.   I clearly remember our Structures professors stressing a few simple facts (it's been 15+ years, so please excuse my relative-layman's paraphrasing):

1) The recent California quakes had had durations of 15-20 seconds, at a level of Richter 6.7-6.9; we had all seen the devastation they caused.

2) The 'recent' (i.e.: the past 3000 years or so) geological record in Oregon and the Pacific NW registered quakes at high 8-to-low-9 magnitudes, sometimes lasting 30 seconds or more.  

3) Long quake durations in loose soils set up the kind of vibrations and rolling harmonic shock waves which can lead to soil liquefaction (where everything holding the buildings up, however sound the buildings themselves may be, turns to soup - try shaking seemingly solid wet sand in a plastic cup).

4) Oregon's seismic codes were quite new, many strengthened or even initiated in response to Loma Prieta.  For most of the development of the state and until well after WWII there had been essentially no seismic codes and buildings were built to the same standards as their eastern counterparts.

5)  If any of us moved to Portland upon graduating (as most did - it was and is a great city), we needed to know that the city had risen on the richest alluvial agricultural soils in the Willamette valley (go figure), and was thus at a risk for soil liquefaction in a sustained quake that would make what happened to the SF Marina District (mostly lowrise housing on similarly loose manmade fill) pale by comparison. 

6) Their practical advice, as I recall it: Live on top of a solid hill or other bedrock, away from the river, in a wood-frame house or in a brand-new steel-framed building, built to Oregon's then-new seismic codes.  This wasn't going to prevent those buildings being effectively destroyed in a serious quake, but might well save our lives for the relative elasticity of wood and steel construction and the more modern code measures taken to prevent actual building collapse.  As one of your earlier commenters noted, the American tradition in seismic engineering, unlike the Japanese, is geared to prevent loss of life but not property loss. 

7) All those incredibly cool old brick loft buildings down along the river and up into the lower parts of NW Portland were built long before WWII with largely unreinforced loadbearing masonry exterior walls and interior framing of timber or reinforced concrete not designed to any seismic standards.  Not the place to be in  a quake.  Retrofits were only just beginning at the time in response to the CA quakes and the new codes, and generally only when mandated by significant renovations.  Even then, given the risk of soil liquefaction, it was debatable how effective such measures would be in a really big quake.

Here in New England, we have quakes (again, a pretty big one in the 18th c.), but they tend to be short, sharp shocks running through bedrock - nowhere near the long-duration rolling killers of the Pacific Rim.  Our codes are also getting to the point of being as responsive as those prevailing in the Northwest, including requiring retrofits to historic buildings when they're renovated.  I don't worry overmuch about an earthquake in Boston, though it has the potential of doing some serious property damage, particularly to loadbearing unreinforced masonry buildings.  At the likely magnitudes and durations here, however, the secondary effects such as water and gas main leaks are more worrisome than direct quake effects.  That's not the case in the Pacific NW, which shares a violent seismic history with the rest of the Pacific Rim.

By the way, those earthquake buttons, if working properly, can be a big help: they're meant to save you from harm from the elevator itself and/or being trapped in it, by getting it to the nearest floor, opening the doors, and shutting the thing down/stopping it in place.  Now, there's not much they can do for the rest of the building, but that's not nothing.

There's little point in living in fear of all this or screaming for instantaneous fixes.  What measures can be taken can only happen gradually, given the staggering costs and competing pressures.  Disasters like the Japan quakes strike with little warning and may come tomorrow or in 300 years, but it does help to be aware that they DO happen, and educated on the best methods to react, as it could save one's life in the moment.

(Photo by Flickr user Ian Sane)