Earthquake

To construct a house or building under static conditions, the materials need only to be stacked up, attached to each other, and balanced. These kinds of buildings are not designed to accelerate rapidly and change directions like cars or airplanes. Buildings in seismically active areas, however, must be designed and built to withstand the dynamic acceleration that can occur during an earthquake. Large buildings and structures such as bridges, in particular, must be designed so that vibrations arising from earthquakes are damped and not amplified.

Because noticeable earthquakes are rare in most areas, people may not recognize that the objects and buildings around them represent potential hazards. It is not movement of the ground surface alone that kills people. Instead, deaths from earthquakes result from the collapse of buildings and falling objects in them, fires, and tsunamis. The type of construction that causes the most fatal injuries in earthquakes is unreinforced brick, stone, or concrete buildings that tend not to be flexible and to collapse when shaken.

The most earthquake-resistant type of home is a low wooden structure that is anchored to its foundation and sheathed with thick plywood. Some of the traditional architecture of Japan approximates this shock-resistant design, including wooden buildings that are more than a thousand years old. Unfortunately, wood and paper houses can be easily ignited in the fires that are common after large earthquakes. Both unreinforced masonry and shock-resistant wood houses are used by different cultures in areas of high earthquake risk.

Active faults lie under many parts of the world that do not commonly experience earthquakes. The crust under such places as Italy, California, and Central America moves often enough that an earthquake there, although still unpredictable, is not entirely unexpected. But other populated areas, such as the East Coast and Mississippi Valley in the United States, periodically experience earthquakes just as big as those in any earthquake-prone part of the world, although far less frequently.