Can earthquakes be predicted? Many seismologists would probably answer, “Not yet, but eventually.” But to date, nobody has been able to predict earthquakes reliably enough and over short enough time scales to allow the evacuation of threatened cities. Some scientists have entirely lost faith in earthquake prediction. They say that so many factors decide whether a fault will rupture that earthquakes could well be inherently unpredictable in a practical sense.

One basic idea behind quake prediction is that faults send out subtle but detectable warnings before they slip. Scientists have looked at a host of potential warning signals, or “precursors,” including foreshocks, weird animal behavior, and changes in the water table, stream flow, well levels, and patterns of electrical currents in the ground. In 1975, the Chinese government made a successful prediction based on precursors like foreshocks, and as a result casualties from a magnitude-7.3 quake in the Haicheng-Yingkow region were relatively light. In the United States, scientists have hoped to predict quakes by noting changes in the speed of seismic waves passing through at-risk faults.

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