Roberto Quaas, the engineer who installed the seismic monitors, recalled his horror as the earth shook his Mexico City home that morning, then his fascination with the seismic data that streamed into the laboratory. The readings provided, for the first time, an accurate recording of the intensity and type of movements the Earth experiences in a great quake.

Scientists such as [John G. Anderson], Quaas and MIT urban sociologist Diane E. Davis say the effects of the quake continue to reverberate two decades later.

"But fortunately, we had four monitors directly above the fault that broke," said Anderson, now director of the Nevada Seismological Laboratory at the University of Nevada, Reno. "Nobody likes an earthquake disaster, but we were happy about getting the data and learning from it. We ended up with the first digital record of an 8 magnitude quake."