For all the suffering caused by Mexico City's earthquake Sept. 19, the majority of the city's buildings in the hardest-hit area came through with little or no damage, according to Mete Sozen, an earthquake engineering specialist from the University of Illinois who surveyed the city immediately after the tremors.
Of buildings more than five stories tall, fewer than 5 percent were damaged, Sozen said. Even more would have survived if the quake had not come in the unusual form of 20 pulses lasting about two seconds each. During each pulse, the ground moved back and forth over a distance of 16 inches.
"There is good evidence that many of the 600 buildings that collapsed hung in there until virtually the end of the earthquake," Sozen said. The fact that damage was not worse, Sozen attributed to the city's relatively tough building codes and to the caliber of Mexico's civil engineers whom he says are among the world's best in earthquake engineering.
Sozen said he disagreed with earlier opinions that the engineering of many buildings was inadequate because the building codes were ignored. "I didn't see a single building that I thought was rotten," he said.
Still Sozen called the quake "the worst by far" that he has seen. Sozen, who was born in Turkey, said he "grew up with earthquakes" and has visited most of the major quake sites since he became a professor of civil engineering at Illinois in 1953.
Damage in Mexico City was largely confined to an area in the center of the city that is built on an ancient lake bed of deep sand that "wobbles like jelly" when a tremor passes through. In the center of the 20-mile-wide lake bed, however, one 43-story-tall building survived intact. It was built in 1954 according to an earthquake-resistant design by an Illinois engineer. It is light and flexible and stands on 361 concrete pilings that were driven 117 feet into the ground.