Tag: cripple walls

South Napa v.s. Cascadia- and our need for seismic upgrades in the Northwest

On August 24, 2014, a magnitude 6.0 earthquake struck near the California city of Napa. It was subsequently named the South Napa Earthquake. One person died and 200 were injured as a result of the quake. Damage was in the range of $300 million to $1 billion- not an insignificant amount.

Much of the damage associated with structures occurred in brittle buildings like those constructed with URM (brick) or with stone-clad veneer. But there was a good deal of damage to homes and other wood-framed structures, also.


Collapsed chimney from the South Napa Earthquake.  (See more pictures here)

I read an article recently revisiting damage from this earthquake, and I couldn’t help but notice some basic statistics and compare them to our Cascadia threat looming off the coast.

Consider just two data points: Ground accelerations and duration of shaking.

The recorded peak ground accelerations during the South Napa earthquake were .61g (61% of gravity).  The significant shaking lasted for less than 10 seconds.

Compare this to a Cascadia Subduction Zone earthquake:

  • Ground accelerations in the Portland area are expected to be around .75g. The shaking will be greater in areas with soft soil, which comprise a good portion of the metro area.  Areas near the rivers- the Columbia, Willamette, Tualatin, etc are also prone to liquefaction, which will further increase damage. Ground accelerations will also generally increase as you move further west.
  • Duration of shaking will be measured in minutes, not seconds. If the full subduction zone ruptures, the shaking could last as long as five minutes.

What does this simple comparison tell us? It should be a sobering reminder of our need to strengthen our infrastructure in the Pacific Northwest. Consider these points also:

  • California has had multiple earthquakes to help weed out the weaker buildings, so to speak- through damage, repairing, and rebuilding over time. We haven’t even had a “South Napa” (i.e. magnitude 6.0) in the Portland area in recorded history. As a result, we have an excessive amount of weak structures still hanging around.
  • Liquefaction will likely be a huge source of damage during the Cascadia quake. Liquefaction damage was limited in the South Napa earthquake due to drought conditions, but it was a significant source of damage during the 1989 Loma Prieta (magnitude 7.0) earthquake and the 2001 Nisqually (magnitude 6.8) earthquake near Olympia, Washington.
  • The need for retrofitting of homes by strengthening cripple walls, providing foundation anchorage, and using blocking and framing connectors to create an adequate load path is very much needed in the Pacific Northwest. Every significant California earthquake produces this type of damage.
  • 1800 URM (brick) buildings in Portland alone will all likely have significant damage unless they are strengthened. This has been known for at least 20 years, but only a small percentage… I believe it is less than 10%… have been adequately retrofitted.

Rogue One, structural engineering, and earthquakes

Most structural engineers have experienced a glazed-over look in someone else’s eyes when describing what they do for a living, followed by a response like, “so, you’re an architect?”

There remains ignorance in the public about what structural engineering (and engineering in general) is for.  Other engineering disciplines may be even more confusing; I doubt most people could define the term, “geotechnical”.  Personally, I’m still not 100 percent sure what an industrial engineer does.

I think the fault of this ignorance lies primarily with engineers.  We have an incredibly cool profession and if people understood better what we do, we would probably make more money, quite frankly. Especially if we were passionate about taking our skills and orienting them toward serving the community, region, and world to make it a better place (which is the reason all professions should exist).

Structural engineering seems to be making more inroads into the public sphere in recent years.  It’s always amusing when Hollywood addresses your career. This happened in the latest Star Wars movie, Rogue One (slight spoiler alert if you haven’t seen it).  The movie specified a large building, which reminded me of a dark version of a Dubai hotel, as a site dedicated to structural engineering (among other things) for the Empire.  And there was also the scene of a group of engineers (in lab coats?) being assassinated for apparent faulty design of the Death Star.  Considering the fact that this Death Star weakness led to the downfall of the Empire in subsequent episodes, this was understandable using Imperial logic, I suppose.

The Structural Engineers Association of Oregon has this clear statement defining the profession of structural engineering (good job, whoever wrote it):

Structural Engineering is the practice of analyzing and designing buildings, bridges and other structures to resist forces induced by gravity, wind, and earthquakes and to safely transfer these forces to the ground.

See here for more: http://www.seao.org/resources/aboutstructengr/

Regarding engineering in general, there are a number of good definitions online, but here is my very simple one:

Engineers apply science and mathematics to the real world to solve real world problems.

Engineers and the engineering profession should act as a bridge between the theoretical realm of science/ mathematics and real life.

Consider the large problem of an impending Cascadia megaquake. The science indicating that these earthquakes have happened and that the subduction zone is locked and building up energy has been settled for about 20 years.

Emergency management at the state and federal level has been aware of the threat for a long time also.  The Oregon Resilience Plan, which was a state funded plan addressing the effects of a Cascadia megaquake and its consequences, was published in 2013.

Journalists helped disperse the information about this topic into the homes and hearts of Pacific Northwest residents (thank you Sandi Doughton and Kathryn Schulz, to name two).  For the last couple of years, there has been more mainstream awareness of this issue than ever.  And my experience has been that people are still baffled by the topic and wondering what to do about it.

Here is my exhortation to engineers, particularly those involved in the disciplines of infrastructure (civil, structural, and geotechnical at the forefront). The Cascadia earthquake threat is large enough to involve all of our individual efforts for years. Please consider what part you can play in increasing your personal, community, and regional resilience. We all know more than the average person about earthquakes and what they do to the ground and to structures. Don’t hide in your cubicle or office. Do what you can with your career to help and you will be saving lives when the earthquake happens.

In Portland, engineers know that there are about 1800 URM (brick) buildings which may partially or completely collapse in a large earthquake.  We know many older homes have weak cripple walls, dangerous unreinforced chimneys, and “soft story” weaknesses which will result in damage, injury, and in some cases, loss of life. We know there will likely be long term loss of power and drinking water. We know industrial areas are set to contaminate our rivers with millions of gallons of liquid fuel. Wow, that’s just the tip of the iceberg. Let’s get to work.

Engineers are a key to helping bridge our gap between what we now know (the science) and resilience. But not just engineers… every one of us can help and I would argue that we have a duty to make steps toward preparedness.

Science =>  =>  =>  => => (our gap)  =>  =>  =>  =>  => Resilience

Journalists

Engineers

Emergency Planners/ Responders

City and State Leaders

Heavy Industry

Everyone

You and me