Earthquakes and Resonance

An earthquake with a magnitude of 8.5 struck Mexico on September 19, 1985. Mexico City, 250 miles from the epicenter, sustained considerable damage. A high percentage of 6- to 15-story buildings suffered damage while a very small number of one- and two-story buildings were damaged. A 48-story building experienced only minor damage—a few broken windows. While many variables affect the amount of damage a building suffers as a result of an earthquake, the natural frequency of a building is a major contributing factor.