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Soft Stories: Earthquake Prone Architecture

Some of us have been around Santa Cruz long enough to remember the Loma Prieta Earthquake. This catastrophic event sent shock waves through our local and state-wide government, causing a surge of earthquake-safety related building code additions and modifications. However, there are still architectural designs that were build before these changes which remain highly susceptible to earthquake damage. If you plan to buy or currently own real estate, it’s imperative that you know about these weaknesses.


Soft story buildings have a parking or commercial space (often with large glass windows and little structural reinforcement) on the first floor and are some of the most susceptible structures to shaking damage in an earthquake. These buildings were build before recent codes and a number of cities have taken action to inspect and reinforce them to prevent future damage. Here in Santa Cruz, building codes have been updated to ensure that new construction is safe. However, existing buildings have no inspection or retrofit requirements. The county does warn about soft story buildings in its Earthquake Preparedness Guide found here.


San Francisco, Los Angeles, Oakland, Berkeley, and others have taken action to ensure these buildings are evaluated and properly retrofitted. It may be time for Santa Cruz to consider doing the same. Why? A new model was recently created by a group of national and state geological organizations which predicts the following probabilities of earthquakes in the next three decades. The results may shock you.


See this report for a description of the model and page 4 for an explanation of the table.


While it’s challenging to know when and where the next major earthquake will take place, according to this article, it is possible that a major CA quake could happen in the next few years.


Here are some example of soft story housing damage in the last major Loma Prieta Earthquake:



If you live in a soft story building, either as a renter or owner, you should be aware of the risks involved. During the Loma Prieta Earthquake, soft story buildings were amongst the most susceptible to earthquake damage. Soft-story collapse can have particularly disastrous consequences considering that they crush cars and kill people occupying the lower open areas, not to mention the costly damage to the building itself.


You may be asking, “What do I do if I live in one of these buildings?”

The fix is called a seismic retrofit and according to this contractor usually includes:

  • Adding a steel moment frame, concrete footing and drag line to keep the 1st floor from rotating and collapsing
  • Adding plywood or concrete shear walls to existing or new walls
  • Replacing existing support columns
  • Adding continuity ties
  • Removing and replacing finishes as required for our work

Here is a link with steps to follow if you know or suspect that you own or live in a soft story buildings.

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