The 1964 Alaska which lasted a record breaking 4 1/2 minutes jolted this house off its foundation and continued to shake it violently minutes afterwards. If someone had retrofitted this house to keep it on its foundation before the earthquake it would have remained more or less intact. This house was built before building codes protected houses against earthquakes from the first floor up. Even then, the walls did not collapse, the roof did not cave in; even the windows did not break. Many people worry about this even though there is no empirical evidence to support this fear.
When this old pre-building code house held up so well, you can imagine how well a modern house built according to earthquake conscious building codes will hold up. In other words, unless you are on a steep hill, have living area above a garage, there is little reason to worry your house will be severely damaged in an earthquake so long as it can be kept on its foundation. The whole purpose of a retrofit is to keep the house on its foundation. If this is properly done the potential for severe damage is practically zero.
Why so little earthquake damage?
The honeycomb of cross-walls in hallways, bedrooms, bathrooms, kitchens etc prevent collapse of the living area. The house itself has walls, a ceiling, and a floor which are all attached to each other. The house with its ceiling, floor, and walls is a cube and the rooms inside this large cube are also cubes. Cubes are a very strong geometric shape which is why houses from the first floor up suffer so little structural damage if they remain on their foundations. significant damage to the main house.
While working for FEMA the author inspected this house and it held together so well that the windows did not even crack. The interior was a different matter as you will see in the photo below.
Same House: earthquake damage on the Inside
Even if the house holds together well, if it falls off the foundation, it can still sustain damage to interior walls, plumbing, and electrical systems which can be catastrophic.
The author was the FEMA inspector who evaluated the beautiful house below after the 1989 San Francisco Earthquake. Two weeks after the evaluation I drove by and saw an empty lot.
Cripple Wall Collapse Photos
Below are some Examples of Homes that fell off their Foundation either because the cripple walls were not braced with plywood, were not bolted, of the floors were not attached to the cripple walls.
In the photo above, look at the top of the concrete steps, then see the porch which is a few feet below it. This is the first sign that the cripple wall has collapsed.
Prepare for aftershocks. The earthquake you just felt is probably only an appetizer