Barry Streek
Nearly 4 000 movements of the Earth, scientifically labelled as “seismic events”, have happened in South Africa over the past six years, 630 of them last year.
But the majority of them are small and insignificant.
Although one of these events recently caused a house to collapse in Welkom, in the Free State, when there was movement of 4,5 on the Richter Scale, some occasionally cause cracks in swimming pools and houses.
While the Tulbagh earthquake about 30 years ago recorded 6,7 on the scale, the country has largely been spared serious Earth movements.
“South Africa is not the place where we can expect devastating earthquakes,” said Dr Nok Frick, chief director of the Council for Geoscience.
Most seismic events have been recorded at places where mining has taken place or is still occurring, but others have been recorded at known geophysical faults.
One of the areas where events have been recorded is in the vicinity of the radioactive waste site at Vaalputs, about 100km south-east of Springbok in the Northern Cape, but Frick said none of these was at the actual site.
Seismic events are recorded at the seismological station at Boshof in the Free State. The station came into operation during 1993, Minister of Arts, Culture, Science and Technology Ben Ngubane said in reply to a question in Parliament.
He said between 1995 and last year 8?604 seismic events were recorded at the station and 3?957 of them were located in South Africa. Last year 1?409 events were analysed at the station.
The station also contributes to data used to locate large global earthquakes with more than 900 events between 1995 and 1999.
Between January and March this year a further 358 seismic events were analysed, of which 74 were in South Africa.
“Seismic” is defined as something relating to earthquakes or other vibrations of the Earth or its crust.
A further 7?453 seismic occurrences were recorded by South Africa’s Antarctica station, but none of these were located in South Africa.
Ngubane said the Boshof station had also recorded 14 nuclear explosions between May 1995 and May 1998 four by China, six by France and two each by India and Pakistan.
Frick said because these events had been recorded for only 100 years, it was theoretically possible that a large seismic movement could occur in South Africa but this was unlikely.
The Council for Geoscience also monitors dams and in South Africa they are “very stable”.
The council researched sites for Eskom when it was investigating potential nuclear sites because seismic movements were potentially the biggest risk at nuclear plants.
Frick said South African cities did not have any inherent seismic risk but research was being done at coastal cities, such as Durban, because of the potential consequences of a large earthquake for a city built on sand.