Undermined City

In Johannesburg a tremor ran through the earth. It shook tall office buildings, cracked walls, swung chandeliers, made restaurant waiters spill the soup. Women screamed, and tourists sprang to the.'r feet asking: "Is it an earthquake?"

Such tremors are not normal earthquakes; they are specialties of Johannesburg. The City of Gold shakes more or less continually because of "rock falls" and "rock bursts" in the great mines under its skyscrapers. It gets from six to ten tremors a day. Most of them are less severe than the worst tremor last fortnight, which registered "four" on the scale of earthquake severity, and was equivalent in release of energy to the explosion of 4,000 tons of dynamite.

The gold-mining companies sometimes claim that the tremors have nothing to do with the mines, but Johannesburg's Bernard Prince Institute of Geophysics points out that there are 200 sq. mi. of gold workings under and close to Johannesburg. They slope down to 9,000 ft. below the surface. Often their roofs collapse or the rock of their walls shivers into flying fragments. "When you feel a tremor," said one engineer, "it may mean that under your feet men have just died as the rocks fell or as walls closed in on them."

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