The most historically severe earthquake that occurred in South Africa was in the northeast of Cape Town on September 29th, 1969. The earthquake had a magnitude of 6.3 and took 12 lives and resulted in extensive damage in local towns. Another 6.3 magnitude earthquake occurred closer (10 km) to Cape Town on September 4th, 1809 at the Milnerton Fault (where the Cape Town stadium now is).
Figure 1: 1809 Earthquake [Available From:Â http://capetownsquake.blogspot.ca/2011/05/cape-town-earthquakes-and-potential.html]
Cape Town Geoscape 