Posting in Architecture
Apartments sitting above parking garages are on flimsy ground and should be upgraded, according to researchers at the University of California at Berkeley.
The quake in Japan brought up a previous talk: What if a big quake hit California? A few years ago, the discussion of the possibility of a big earthquake hitting California emerged after the United States Geological Survey published a study on the topic. California is prone to earthquakes because it rests on the boundary between two of the earth's major tectonic plates - the Pacific and American Plates.
The study, The Uniform California Earthquake Rupture Forecast, was based on the 2007 Working Group on California Earthquake Probabilities. Looking on earthquake histories and the movement of the fault lines, the group concluded that "there is a probability of more than 99% that in the next 30 years Californians will experience one or more magnitude 6.7 or greater quakes, potentially capable of causing extensive damage and loss of life."
As we've witnessed, the earth will grumble when it wants to. The only thing we can do is to prepare for it and have early warning systems in place. Dana Butrock, an architecture at the University of California at Berkeley chimed in on how to be prepared for a big earthquake:
SmartPlanet: Can you explain why California is vulnerable to a big earthquake?
DB: Our understanding of what happens to buildings in earthquakes literally changes with almost every new event. As a result, we have learned a lot that is not reflected in our building stock. In the case of buildings more than 30 years old, which make up much of California's landscape, decisions were made during design and construction that we would not make today. The result is that unless they have been upgraded, those older buildings are generally more dangerous than a brand-new building, just as a car that is 30 or 40 years old is less safe than a car made today.
SmartPlanet: How has our understanding of earthquakes (and the science behind them) changed how we go about building construction?
DB: We first learned how to make buildings stronger and make the piece of the building work together. In houses, we use rigid panels (especially plywood or OSB) to create strong walls. We anchor buildings to their foundations, and use steel straps to tie the rigid planes together, making sturdy, 3-dimensional boxes.
After the 1995 Hanshin earthquake in Kobe, we realized that sometimes trying to be strong enough was impractical. So we developed dampers and shock absorbers, things like base isolators, to help larger structures ride out earthquakes without failing.
SmartPlanet: Why are homes and apartment buildings that were built above parking garages the most vulnerable?
DB: In the 1970s (that is, more than 30 years ago), California was booming and the car was king. That resulted in apartment buildings sitting above parking garages, with what we now understand as a flimsy structure on the ground, in order not to interfere with cars' movement. Today, we call those "soft story" buildings. Some communities, like Berkeley, are working to get these structures strengthened. But many building owners, because of the cost, are unwilling or unable to make those structures safer, and there is little public money to serve as an incentive.
SmartPlanet: What needs to be done? Do we need to upgrade the buildings?
DB: We have pretty good codes right now, but not every building matches them. We need to find ways to encourage retrofits. Berkeley has done a pretty good job of that for single-family homes, using incentive programs. But there are a lot of schools and hospitals that we want to be safe in a strong quake, and far too many questions about whether they are.
Related on SmartPlanet:
- Robots to the rescue: searching for survivors, checking on structural damage in Japan
- A meltdown-proof nuclear reactor may alleviate fears
- Understanding the Chilean earthquake, on the ground and in the lab
- Japanese nuclear plant damage in earthquake, needs coolant
- Japan’s partial meltdowns and the future of nuclear power in the U.S.
- How Japan’s early warning system detected the earthquake
- Japan’s strong building codes kept millions safe
Mar 15, 2011
The faults in California (except along the far northern coast) are slip-strike faults and are unlikely to produce an earthquake much above the 8.0 range. It takes a subduction zone/megathrust fault to produce earthquakes in the 9.0 range. Subduction zones are found off the coast of Chile, the Northwest Coast, Southern Alaska, Japan, and Sumatra. It's doubtful there will ever be a 9.0 quake in San Fransisco or south of there until you get to Peru/Chile in the foreseeable future.
...but at least there is some degree of preparedness. But how prepared are we elsewhere in the country, where regular earthquakes are rare, but large earthquakes are also possible. For example, the "New Madrid Fault" near the MO, AR, and TN boarder has the potential to devastate the Midwest with earthquakes in the 7-8 range, which would likely be more devastating than a similar quake in CA, simple because building codes in this region do not recognize the threat. Large quakes historically hit this area every 100 years or so, and we're more overdue than in CA.
I've been hearing that for at least 30 years. California has had lots of quakes in the 5-6 range, and then a 7.1 quake that devested Oakland in 1989, killing 60 people. If and when a 9.0 hits San Francisco, expect Sendai-like resuslts, except that the Californina coast is not low-lying like Japan or New Orleans or Florida.