The tremor was recorded at 22:14 GMT on Wednesday, 156 kilometres (about 100 miles) southwest of the island of Bristol. The epicentre of the earthquake was located at the depth of 35 kilometres.
As no people live on the South Sandwich Islands, the earthquake caused no victims and destruction.
The South Sandwich Islands are facing seismic activity caused by the subduction of the South American Plate beneath the South Sandwich Plate.