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Johannesburg - The Council for Geosciences has warned that more tremors and aftershocks are expected in the coming days.
This follows the 5.5-magnitude earthquake on Tuesday in Orkney and Stilfontein in the North West mining area, in which one person died.
“We are monitoring. It will continue for days, if not months,” said Michelle Grobbelaar, manager of the council’s seismology unit.
“More tremors are expected. We can expect one of the same magnitude in future, we just don’t know when. We cannot predict,” she said.
An aftershock hit the township of Khuma, near Orkney, on Tuesday night.
People gathered outside one of the houses that was destroyed, and screamed as the ground shook again. Two Orkney mines are temporarily closed after 34 miners were injured in the quake.
Leshomo Makhaola from Lesotho was killed when a wall fell on him in a disused building and at least 400 homes were damaged in Orkney, particularly in Khuma.
On Tuesday night the Matlosana municipality used ambulances to ferry people to emergency housing.
The quake was felt across Gauteng and North West, in KwaZulu-Natal, the Free State and as far as Lesotho, Botswana and Zimbabwe.
Some experts said it was probably mining-related.
On Wednesday morning AngloGold Ashanti said they halted operations in the two mines most affected by the quake, to check whether it was safe for miners to return underground.
The shift that would normally go underground at 4.30am did not report for duty.
Instead, rock mechanics and engineers were to go underground at Moab Khotsong and Great Noligwa mines to inspect whether the structures were stable enough and safe for miners to resume their work.
AngloGold Ashanti spokesman Stewart Bailey said they could not say just how long the inspection would take. “Infrastructure assessment will be starting this morning and will take as long as it takes. We will be putting human beings down there so we have to ensure that it is totally safe. There will be a thorough check of all infrastructure,” he said on Wednesday morning.
While Bailey said it was too early for a damage assessment, their shaft inspection determined the lifts were in good condition. He also said there was an ongoing seismic assessment of the mine.
Thirty-four of their miners were injured during the tremor on Tuesday.
“Eighteen were kept overnight in hospital for observation and the rest were treated and discharged. We are going to be extra cautious before they return so that everyone goes back to work without any incident,” he said.
The Chamber of Mines said AngloGold was the only one of their members to report problems.
The Council for Geosciences measured the quake at 5.5 on the Richter scale, while the US Geological Survey put it at 5.3.
Professor Andrzej Kijko, the director of the University of Pretoria’s Natural Hazard Centre, said the tremor was believed to be mining-related. He said there were two types of seismic events in South Africa – mining related and naturally occurring – but the natural events did not occur often here. He said Tuesday’s quake was big for a mining-related event.
The largest naturally occurring quake was the 1969 quake in the Tulbagh/Ceres area, in the Western Cape.
“In a place like Klerksdorp, you mine in a flock and you accumulate stress (to the Earth) and that triggers natural stresses, which led to the tremors,” said Kijko
North West Premier Supra Mahumapelo said Khuma in Orkney was the hardest hit.
North West authorities said three clinics were damaged in Klerksdorp and Stilfontein.
ER24 spokesman Werner Vermaak said they were called to help with evacuations at 11 mines. No miners were trapped and there were minor injuries.
Orkney is in the Matlosana municipality, where authorities had their hands full.
Tommy Deysel, assistant director of the Fire, Rescue and Disaster Management at the municipality, said while they were trying to help people, power was cut off.
When the power was restored a few hours later, it was in “bits and pieces”.
They also had to evacuate 100 nursing students from their residence to a community hall where they had to be accommodated.
“That nursing home is not old but it had so many cracks, I would not even sleep there myself. We had to transport some of them in ambulances to the hall.”