7.2: Is Your Home Ready for an Earthquake?

• 7.2.1: How Safe is Safe Enough?

  Chances are two out of three that you’ll be at home when the next big earthquake strikes, and one out of three that you’ll be in bed. So, your home’s ability to withstand an earthquake affects not only your pocketbook but also your life and the lives of those who live with you. If you are an owner or even a renter, you can take steps to make your home safer against an earthquake.

• 7.2.2: Some Fundamentals—Inertia, Loads, and Ductility

  Imagine for a moment that your house is anchored to a flatcar on a moving train. Suddenly the train collides with another train, and the flatcar stops abruptly. What happens to your house? If it’s a wood-frame house, as most houses in the Northwest are, it probably would not collapse, although your brick chimney might topple over. If your house is made of brick or concrete block, unreinforced by steel rebar, then the entire house might collapse.

• 7.2.3: Protecting Your Foundation

  If you have a poured-concrete foundation, hit it with a hammer to check on its quality. If the hammer makes a dull thud rather than a sharp ping, there are thoroughgoing cracks more than one-eighth inch wide, or the concrete is crumbly, get professional help. Let’s assume that the concrete is okay. The next job is to see if your house is bolted to the foundation and is adequately braced. Otherwise, horizontal inertial forces could slide the foundation out from under the house.

• 7.2.4: Soft-story Buildings

  A common failure in California’s recent earthquakes was the two- or three-car garage with living space overhead. Many condominiums have most of the ground floor devoted to parking, with apartments in the upper floors. The large open space at the garage door means less bracing against horizontal forces than in standard walls, so these open areas are the first to fail in an earthquake. A wood-frame apartment building is lighter and fares better than a massive concrete structure like a hospital.

• 7.2.5: Utility Lines

  One of the greatest dangers in an earthquake is fire. Fire caused much of the loss of life and property in the 1906 San Francisco Earthquake and the 1995 Kobe Earthquake, and large fires destroyed property in the Marina District of San Francisco after the 1989 Loma Prieta Earthquake. The problem is natural gas. If gas connections are rigid, they are likely to shear during an earthquake, releasing gas that needs only a spark to start a fire.

• 7.2.6: Strapping the Water Heater and Other Heavy Appliances and Furniture

  Your water heater is the most unstable appliance in the house. It’s heavy, being full of hot water, and it’s tall, likely to topple over due to horizontal forces from an earthquake. Built-in dishwashers, stoves, and ovens might not be braced in place; they may only rest on a trim strip. One homeowner was quoted in Sunset Magazine after the October 1989 Loma Prieta Earthquake: “I assumed built-in appliances are fixed in place. NOT SO! Our built-in oven and overhead built-in microwave slid out.”

• 7.2.7: Safety Glasses

  A major problem in an earthquake is shattered glass windows, which might flex and essentially blow out, showering those within range with sharp glass fragments. An expensive option is to replace glass in large picture windows or sliding doors with tempered or laminated glass. A much cheaper alternative is safety film, which costs about three to four dollars per square foot, installed.

• 7.2.8: Cabinets

  Remember José Nuñez of Molalla, Oregon, who watched his kitchen cabinets blow open during the 1993 Scotts Mills Earthquake, spewing their contents onto the kitchen floor? Magnetic catches often fail. However, inexpensive babyproof catches will keep cabinet doors closed during an earthquake (Figure 11-11). Heavy, spring-loaded latches are advised, especially for cabinets containing valuable dishes.

• 7.2.9: Bricks, Stonework, and Other Time Bombs

  If you live in an old, unreinforced brick house, you are in real danger, and none of the retrofit techniques mentioned above will do much good outside of a major costly reinforcing job. Fortunately, old brick houses in the Pacific Northwest are being phased out of the building inventory; most of us live in wood-frame houses. But one part of your house is still likely to be unreinforced—your masonry chimney. Chimneys collapse by the hundreds during major California earthquakes.

• 7.2.10: Propane Tanks

  Above-ground propane tanks can slide, bounce, or topple during an earthquake, causing a fire hazard from a gas leak. You can reduce the fire danger by doing the following: (1) Mount the tank on a concrete pad and bolt the four legs of the tank to the pad. (2) Install flexible hose connections between the tank, the supply line, and the entrance to your house. (3) Clear the area around the tank of objects that could fall and rupture the tank or its gas supply line.

• 7.2.11: Connections

  One of my most instructive memories of the 1971 Sylmar Earthquake was a split-level house, where earthquake shaking accentuated the split between the garage with a bedroom over it and the rest of the house (Figure 11-16). A common sight is a porch that has been torn away, a fallen deck, or balcony. These connections are the potential weak link in the chain that is your home. Make sure that everything is well connected to everything else so that your house behaves as a unit during shaking.

• 7.2.12: Mobile Homes and Manufactured Houses

  Because these houses must be transported to their destination, they are more likely than an ordinary house to behave as a coherent structural unit during an earthquake. Manufactured houses are built on one or more steel I-beams that provide structural support in the direction of the I-beam. However, mobile homes and manufactured houses are commonly not bolted to a foundation, but instead rest on concrete blocks that are likely to collapse during even low horizontal accelerations.

• 7.2.13: Okay, So What Retrofitting Are You Really Going to Do?

  You probably won’t take all of these steps in making your home safer against earthquakes. Doing everything would be costly and might not increase the value of your home unless it successfully rides out an earthquake. So you might decide to live with some risk.