In the 1985 Mexico City earthquake, the natural frequency of shaking of buildings between 10 and 14 stories high was the same as the frequency of the earthquake waves passing through, and those buildings suffered more damage than did smaller structures. And to make matters worse, the natural frequency of vibration of the ground also amplified the earthquake waves, so that amplification was piled upon amplification, making for a very destructive earthquake. The Cause of the Destruction Most of the damage from an earthquake is caused by the shaking of the ground as waves of energy pass through it. The shaking can be aggravated and lengthened in areas of soft sediment, like the Marina district in San Francisco, or in downtown Santa Cruz. Much of the damage in the Mexico City earthquake of 1985 was caused by liquefaction of the ancient lake sediments upon which the city was built.
More destruction comes from the ground rupturing either vertically or horizontally.
Legislation, however, cannot protect people from unpredictable dangers, such as the landslides and tsunamis that occasionally accompany or follow an earthquake. The massive landslides in the Santa Susana Mountains north of Northridge, California, in 1994 injured no one, but smaller landslides in Santa Monica during the same quake destroyed homes in the Pacific Palisades area.