An earth tremor injured six miners one day before the earthquake that hit DRDGold’s North West operations on Wednesday, trapping 42 mineworkers underground.
Trade unions are enraged that this foreshock was disregarded, but experts say that predictions are “almost impossible”.
By Thursday midday, a team of 1 000 rescue workers, including volunteers from among the workforce, had evacuated all the miners except one, who was still unaccounted for by the time the Mail & Guardian went to press. Two of the three stricken shafts at Buffelsfontein and Hartebeesfontein had been reopened.
But Dr Andrzej Kijko, head of the seismology department at the Council for Geoscience in Pretoria, warned that “there will still be a lot of aftershocks and a more substantive investigation should be done” before mining resumes.
The mining company “needs to understand whether all the [geological] stresses have been released. I don’t want to interfere with the management there, but from a physical point of view the reality is that there could be residual stresses. They should be very careful.”
The earthquake occurred at 12.15pm on Wednesday more than 2km underground, where 3 158 miners were working — most were able to escape. There was one fatality, but none of the trapped miners suffered major injuries, said DRDGold spokesperson Ilja Graulich.
Rescue team leader, Darren Vorkel, said that they travelled 6km underground before reaching the miners, a task that took 12 hours and involved digging rocks away with their hands.
The National Union of Mineworkers (NUM) is incensed about the quake and is blaming the mine management, which, said the union, has a “terrible health and safety record”.
“[On Tuesday] the whole area was affected by a seismic event and six mineworkers had to be treated for injuries,” said Hoyce Pundulu, NUM regional secretary at Klerksdorp. “[On Wednesday] we experienced another seismic event that encompassed all DRDGold’s operations in North West. This begs the question as to whether DRD has any equipment at all to detect these seismic events and therefore embark on precautionary measures.”
When asked about Tuesday’s tremor, Graulich said, “There is permanent activity underground … [Although] we have a seismic monitoring machine in the ground on a permanent basis [NUM’s assertion that the quake could have been predicted is] absolute rubbish.”
Kijko noted that DRDGold mines in North West “have world-class seismic monitoring equipment” and that Tuesday’s tremor was a foreshock, which are characteristic of earthquakes and are “usually located in the area of the future incident”. However, he said it is very difficult to predict the place, the size and the time of a future quake; “unfortunately the science of prediction is only just starting”.
Seismologists divide the origin of earthquakes into two categories: natural causes and mining-related. “The magnitude of Wednesday’s earthquake tells us that it was mining-related,” said Kijko. “Mining activity probably triggered an old fault line.”
The last major earthquake in South Africa was in Ceres in the Western Cape in 1969 and measured six on the Richter scale. Kijko explained that Wednesday’s quake was “one unit less, which means it was 30 times weaker than the 1969 disaster”. The first aftershock, measuring four on the Richter scale, occurred at 7pm on Wednesday night.
Graulich said it was too early to gauge the financial implications of the earthquake for DRDGold.