18/08/2014. Professor Ray Durrheim talks about the previous large mining-related earthquake which also registered 5.3 on the Richter scale in the town of Orkney. Picture: Thobile Mathonsi

Pretoria - Experts believe that more than 100 years of mining activity could have led to the 5.5 magnitude earthquake which shook South Africa earlier this month.

The experts have also blamed poor workmanship for structural damage in the Earth’s crust.

The earthquake was centred on the mining town of Orkney.

Experts now believe that mining activity could be directly linked to the earthquake as a result of the stresses applied on the Earth. The quake damaged scores of buildings and households in and around, and resulted in the death of a 31-year-old man.

CSIR experts said on Monday that it was unlikely for South Africans to experience another earthquake of that magnitude in the next 10 years.

Professor Andrezj Kijko, Tshwane University of Technology’s natural hazard centre director, said the earthquake could have been a result of the different stresses exerted through mining.

“After enough mining, we are creating stresses, more and more stresses, and they are propagating deeper and deeper,” he explained.

Kijko believes stresses are being added to existing stresses which are affecting tectonic movements. These stresses then trigger earthquakes. “We are talking about accelerating earthquakes just by mining.”

A seismologist and earthquake expert, Dr Ray Durrheim, said it was improbable for the country to experience another an earthquake of that magnitude, but also said there was no way of being certain about that. Asked if it was possible to predict another earthquake, Kijko said: “It is possible to predict how often earthquakes take place, but it is impossible to predict where, when, and the size of the earthquake.

“We are not in a position to predict events. We are in a position to answer when you can expect certain events of such magnitude. Another quake can be expected in a period of 10 years, with the main aftershock possibly being 4.5 in magnitude, which can cause damage,” he said.

Michelle Grobbelaar, of the Council for Geoscience, said they were still analysing the data collected from the previous quake. She said about 100 aftershocks occurred throughout the country with the largest aftershock being measured at 3.8 on the Richter scale.

Professor Herbert Uzoegbo, a structural engineer who attended the scene at the epicentre, said most of the houses in the town were not built to withstand earthquakes.

“Some locals in Stilfontein said they experienced vibrations from the mines at least twice a month, which means their houses needed to be built to resist tremors,” he said.

“Poor workmanship can also be blamed for the damages caused by the earthquake,” Uzoegbo said. About 600 houses in Khuma township were damaged. Residents in Gauteng, KwaZulu-Natal, Mpumalanga, the Free State and as far as Botswana felt the quake.

Pretoria News