Standing tall
California in the US is known as the "earthquake country". With hundreds of earthquake faults, it is a global example of what is termed today as "an earthquake community". Starting from the great San Francisco earthquake of 1906, it has gradually established a system that minimises loss of life and damage to property.
Similar is the safety level in Japan, which is even more prone to earthquakes and has buildings as high as 50-60 storeys that are built today. Geophysicists have been able to deploy instruments to measure accelerations and velocities during major earthquakes.
Consequently, engineers know that an effective way to decrease damage is to isolate the motion of the building from the horizontal motion of the ground. They can do this by installing flexible bearings on the foundation called base isolators, which are made of layers of steel and rubber or neoprene. In this mechanism, the base can also be isolated by a sliding surface. Even as the ground moves back and forth, the building does not.
In the 1989 earthquake that measured 7.1 on the Richter scale and struck the Santa Cruz mountains in central California, the Transamerica Pyramid building did not report any damage even though the US Geological Survey instruments installed years earlier showed that the top floor swayed more than a foot. Based on the observation of this earthquake, stronger building techniques were designed.
With new technology available to simulate data since the 1989 earthquake, the US can now record and analyse the entire spectrum of ground motion, both its amplitude and frequency. The first such buildings in the US were the Law and Justice Center in Rancho Cucamonga (1985), California, the Fire Department Command and Control Facility in Los Angeles (1990) and the University of Southern California Teaching Hospital in east Los Angeles (1991).
Though effective, the building cost doubles when this technique is used. It is, therefore, only employed when building special structures such as hospitals and disaster control rooms. During the 1994 earthquake that rocked Los Angeles, a hospital that was built with this technique survived the quake despite being near the epicentre.