The Council for Geoscience says the quake that hit South Africa on Friday morning was 3.8 magnitude, and not 4.6 as estimated by the US Geological Survey (USGS).
"It's the same event. The USGS measurement is done by a machine, and the stations they use are not in as close proximity to the quake as ours, and that's why it's different," council seismology unit manager Michelle Grobbelaar said.
"Once they analyse it, it will start changing."
The USGS said the quake occurred 12km west of Orange Farm, a township south of Johannesburg.
However, Grobbelaar said the quake hit Carletonville, which is about 70km away, at around 1.14am.
"After that, there were several aftershocks," she said.
The two major aftershocks were a 3.2 magnitude at 1.15am, and a two magnitude at 1.16am.
"The other aftershocks were smaller ones," she said.
Earlier, Johannesburg emergency services spokeswoman Nana Radebe said no injuries were reported and they were not called out to help anyone.
ER24 spokesman Werner Vermaak said they were on stand-by after the quake struck but they also were not called out.
On August 5, a 31-year-old man was killed in a mining village near Orkney, North West, when a 5.5 magnitude earthquake struck the region.
At least 34 miners were injured, and more than 600 houses were damaged. At the time, the CGS said more tremors were expected to hit the country in the coming weeks and months.