The earthquake that shook Johannesburg and the East Rand early yesterday was possibly caused by vast amounts of water flooding into underground voids left by abandoned mines.
Many Gauteng residents woke up with a start at about 12.30am because their beds were shaking.
"We were scared to death," said Kobus van Wyk, who woke as photo frames fell from his wife's dressing table.
"It felt as if something flew into the house."
The quake set off house alarms, dogs barking and birds flying.
Michelle Grobbelaar, head of the seismology department at the Council of Geoscience, said the quake measured 3.4 on the Richter scale, which classifies it as a low to moderate earthquake. While the epicentre was in the Benoni-Boksburg area, on the East Rand, it shook late-night revellers' drinks in Johannesburg, and was felt as far away as Centurion, Pretoria.
Grobbelaar said the quake was possibly caused by huge amounts of water filling the mining voids.
The entire East Rand, from east of Johannesburg to Springs, is littered with old gold mines, abandoned because they were no longer profitable.
"The mine starts filling up with water which lubricates the [underground] fault plates. When the plates slip, it causes an earthquake," said Grobbelaar.
Anthony Kesten, spokesman for the Ekurhuleni Disaster Management Service, said no injuries or serious damage was reported.
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