Many of the existing structures situated along earthquake-prone fault lines aren't designed to withstand significant ground-shake. While a few have been shored up with reinforced shells or strengthened internal frames, most have not been done simply because of the cost.
However, that could change. In San Francisco, for example, a 2013 law requires property owners to retrofit wood-frame soft-story buildings at least three stories high that were built before 1978. The city estimates it could cost between $60,000 and $130,000 to retrofit a building. Building owners are complaining about the price, as are some tenants rights' groups which fear rents will increase as costs are passed on [sources: Lin, City and County of San Francisco].
Traditional methods of reinforcing a building relied on strengthening the beams and columns and building the walls with braced frames. But newer methods focus on the foundations. Take the world's largest earthquake-safe building, for instance. At Istanbul's Sabiha Gökçen Airport, a 2-million-square-foot (185,806-square-meter) terminal functions much like a giant roller skate. Instead of being tied to the soil with a traditional foundation, the terminal sits atop more than 300 bearings, known as isolators, on which it will roll during an earthquake. This allows the massive building to move as a whole during a ground-shaking event, rather than undulating in an uneven -- and destructive -- fashion. Essentially, the isolators act as shock absorbers while the structure slowly rolls to and fro, skirting damage during earthquakes up to an estimated 8.0 magnitude [source: Madrigal].
Isolating a building's base, and then dissipating the energy of an earthquake as it travels underneath the building, is key in creating earthquake-proof buildings. In addition to bearings, such as those used under the airport in Istanbul, there are other isolator systems. One such system relies on just a few bearings that travel along curved rubber pads between a structure and its foundation, allowing the base to move during an earthquake while minimizing the movement of the structure itself. Other devices focus on dissipating the energy caused by ground movement, acting as giant shock absorbers between the foundation and building [source: MC EER].
While this technology is becoming more commonplace, it still adds significantly to the building's bottom line. An architectural Web site estimated it would cost $781,000 to retrofit a high school and $17,000 for a 2,300-square-foot (213-square-meter) house [source: Kuang]. If building owners and contractors in the U.S. find the outlay for earthquake-proofing a building high, imagine what this must mean in developing nations.
However, there are ways to apply these principles inexpensively. Safer structures can be built using reclaimed materials like tires filled with stones and placed between the floor and foundation. Walls can be reinforced with natural, flexible materials like bamboo or eucalyptus. And weighty concrete roofs can be replaced with flexible sheet metal on wooden trusses [source: National Geographic].