This home in Santa Cruz, California, damaged in the 1989 Loma Prieta earthquake, shows the effects of a weak "cripple-wall" connection between the upper part of the house and its foundation. Houses without adequate connections to foundations can easily shift during even moderate earthquake shaking, causing extensive damage. For example, pipes and wires may be broken by a slight cripple-wall shift, resulting in fires, water damage, or other problems. Much damage of this type can be avoided by using inexpensive bracing techniques, such as those recommended in the seismic design provisions of building codes. (Photo courtesy of USGS)
What About Building Codes?
America's first line of defense against earthquakes has historically been the construction of buildings that can withstand severe shaking. Cities and counties rely on the seismic design provisions in building codes to ensure that structures can resist earthquakes. The variations in the seismic threat across the country are depicted on maps in building codes as zones of different risk levels. These building-code maps are based on more detailed shaking-hazard maps prepared by U.S. Government scientists.
Shaking-hazard maps can be combined with data about the strength of existing buildings to estimate expected earthquake damage in an area over a given period of time. Although strong earthquakes are less frequent in the Central and Eastern United States than in California, damage in those regions could be catastrophic in a powerful temblor. This is because most buildings and other structures there have not been constructed to withstand severe earthquake shaking. For example, the shaking hazard in Boston is far lower than that in Los Angeles, but the damage to structures throughout the Boston area would be much greater if a strong earthquake struck today. A single earthquake in the Central or Eastern United States could cause as many casualties and as much damage as several earthquakes of similar magnitude in California.
Disasters such as fires, earthquakes and windstorms often prompt upgrades in building codes as people become more aware of the dangers posed by Mother Nature. But the reality is that even the most up-to-date building codes can still fall short of protecting your home against major catastrophes. The situation is even worse for older homes, which were often built before engineers and builders paid much attention to strengthening homes against disasters.
Through the continuing process of refining estimates of the shaking hazard across the Nation and observing successes and failures in building design, scientists and engineers are laying the groundwork for future urban environments that will be safer in earthquakes. By improving the resistance of homes, office buildings, hospitals, highways, dams, and utilities to earthquake shaking, scientists and engineers also help to ensure that communities are able to recover rapidly following a major temblor.
But the bottom line is: The fate of your home -- and your family -- may depend on a few simple methods of strengthening its structure against winds, fire, quakes and other ravages of Mother Nature.
