activation of an old fault ... a secondary effect of mining," said Ian Saunders, a geotechnologist at the Council for Geoscience. Saunders's colleague, seismologist Eldridge Kgaswane, said Wednesday's quake was exceptional in being so severe. "In normal cases you would have a magnitude of 1, 2 or in exceptional cases 3, so this is very exceptional," Kgaswane said. Naturally occurring earthquakes are rare in South Africa. The last major one, which occurred in 1969 north of Cape Town, measured 6.3 on the Richter scale and caused extensive damage, the Council for Geoscience's website said.
