China is one of the most earthquake-prone countries in the world. For centuries the Chinese have tried to predict earth- quakes, but with no success. Then, in 1974, the only accurately predicted earthquake in modern times took place there.

The region near the city of Haicheng in Liaoning Province had been monitored for several years. Seismologists had installed many instruments in the area to record earthquake predictors such as tilting of land surfaces, changes in the electrical activity in the ground, and fluctuations in the magnetic field. Area residents helped the scientists by reporting odd animal behavior or a drop in the well water levels-two things that many believe are precursors to an earthquake.

By January 1975 seismologists agreed, based on the evidence, that there would likely be an earthquake in the near future. Authorities put the city on alert and began preparations for...