Johannesburg - A structural geologist has said that the 5.5 magnitude earthquake that hit South Africa on Tuesday, killing one person and injuring 17, could be considered big, but was not uncommon.
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The quake caused scares in North West mining operations and evacuations in large parts of the country.
"For South Africa, a 5.5 magnitude quake is quite big but its not uncommon," said Herman van Niekerk, a structural geologist from the University of Johannesburg.
"It went on for about 20 seconds or so, but some people say they felt it for a lot longer," he told Sapa.
The quake, one of South Africa's largest magnitude earthquakes in the past decade, was felt as far Mozambique and Botswana.
The Council for Geoscience said its epicentre was in the Orkney region in North West province, where one person was killed.
"It occurred in the Stilfontein, Klerksdorp, and Orkney region [in the North West] and it was quite widely felt... as far as the Eastern Cape," said the Council for Geoscience's Michelle Grobbelaar.
She said more tremors, aftershocks and possibly a second quake of the same magnitude were expected in the coming days, but it was unknown when.
Tweets from News24 users have started coming in that they have felt a second tremor.
"We are monitoring. It will continue for days, if not months," she said.
"More tremors are expected. We can expect one of the same magnitude in future, we just don't know when. We cannot predict."
Citizens in Gauteng, KwaZulu-Natal, and the Free State reported feeling the quake.
ER24 spokesperson Luyanda Majija said the body of a 31-year-old man was found in an old mining village in Orkney following the quake.
"He was found lying under some debris," she said.
No trapped miners
Majija confirmed that there were no miners trapped in mines around Orkney following the earthquake.
"There are no entrapments. Most miners working in various mines have been brought out," she said.
"Most shafts have been evacuated."
According to AngloGold Ashanti 17 employees at it's Vaal River operations were injured.
"Early indications are that 17 of our employees at the Great Noligwa and Moab Khotsong mines sustained minor injuries and are being attended to on site by emergency medical staff," it said in a statement.
"We are in the process of establishing telephonic contact with all mining crews, in line with our safety protocols."
Johannesburg emergency services spokesperson Robert Mulaudzi said the quake was felt in most parts of the city.
"The city has not received any reports of injuries, or collapsed building. However, we will be monitoring the situation."
In Tshwane, the offices of the public protector and two buildings at the University of Pretoria were evacuated.
Free State police spokesperson Captain Steven Thakeng said reports were received from Thabong and Welkom that pupils were evacuated from schools as a precaution.
The United States Geological Survey said on its website the quake was felt as far off as Botswana.
"This earthquake is severely dangerous because the epicentre is located right below Orkney and Klerksdorp," it said.
Unconfirmed building collapse
It reported that severe shaking was felt in Klerksdorp and there was an unconfirmed report of a building that had collapsed, where people were trapped.
Another report on the website said a school building in Klerksdorp shook so badly that pupils were thrown off balance.
In Ventersdorp, about 55km from Potchefstroom, resident Solomon Mere said he was at work when they heard a heavy strange sound approaching.
"It was as if something heavy was coming. We left our office and rushed to the street to see it. We could not see anything and suddenly the earth vibrated under our feet," he said.
In Durban, the 32-storey Durban Bay House, one of the tallest buildings in the city, was evacuated.
"I felt it. I thought I was going mad. I stood up and saw my colleagues rushing out," said Lungelo Xaba, who works on 17th floor of the building.
Andrew Trench, the editor of the Witness newspaper, wrote on facebook: "We all ran from our building when the tremor hit here. It was crazy. I thought our building was collapsing."
The Folha de Maputo website in Mozambique reported that a number of buildings in the capital city were evacuated.
It quoted an unnamed office worker from an office building as saying: "Suddenly I just felt the chair to take me to the corner of the room and immediately got up and told the others who were also alarmed by the shudder of the building."
Van Niekerk said the quake was an indication that the earth's crust was under stress.
"It tells us about the stress conditions in the earth's crust at the moment, and something is putting it under stress."
Van Niekerk said one of the "stresses" could be what was happening in the Great Rift Valley, in the north of Africa, where violent seismic activity was reportedly tearing the continent in two.
"That will cause some other stresses throughout the earth's crust, and with this stresses you might have very old structures - older than gold mines, which were there billions of years ago - that could be remobilised to relieve stresses."
Van Niekerk said he did not believe that mining was to blame for the quake.
"We've had 5.2 [magnitude] in Welkom in 1976, we've had 4.7 in Carletonville in 1992, and in 2011 we had [a] five magnitude in the Augrabies, in the Northern Cape."
According to the Council for Geosciences, a 5.3 magnitude earthquake struck the same region in the North West in 2005.
More recently, A magnitude four earthquake struck the Johannesburg region in November last year, while one with the same magnitude struck Bela-Bela in Limpopo in December.