Forensic experts and officials from the Council for Geoscience were still investigating and are likely to have answers on Thursday morning on the near-death incident that injured five people, one of them critically.
The pedestrian bridge was built in 1978 but has been decommissioned for many years.
Although these various reasons are being bandied about, the Council for Geoscience’s Dr Eldridge Kgaswane said that a tremor of 2 or less on the Richter scale, as had been experienced on Tuesday, and which was not widespread, could not have been the cause of the collapse.
“It would take tremors of over 6 or more to have caused the bridge to collapse.”
The bridge, he said, was on Central Rand where there had been a lot of mining activity many years ago but which has since not occurred.
“Water fills these cavities over the years and we sometimes have fluid-induced water movements which cause the tremors,” Kgaswane said
It could also be that the collapse could have caused the tremor, sending out after-shocks.
“We will start investigations this morning,” he said.
Local ward councillor Gill Humphreys said the bridge had been unused for many years.
“Over this time, it has been stripped of nuts and bolts and all steel reinforcing.
“We are questioning why Sanral did nothing to ensure the safety of the bridge, as this almost certainly caused the collapse,” she said.
The SA National Roads Agency (Sanral) said the bridge was out of use because of changed land use development alongside the freeway.
“It was regularly inspected in terms of Sanral’s bridge management system.
“The bridge was inspected in July 2016 and nothing was found that warranted action,” said Vusi Mona, general manager of communications.
The road was reopened to traffic on Thursday morning.
William Ntladi, spokesman for emergency services in the City of Ekurhuleni, said crews of tow-truck drivers, metro police officers, and engineers from Sanral and the Department of Labour were on site on Wednesday.
“The heavy-duty trucks spent the day and most of the night towing damaged vehicles and trucks away. Clean-up of the damaged concrete has started and will continue through the night,” he told The Star on Wednesday.
Ntladi said metro police officers had been strategically placed around all major intersections, diverting traffic onto other routes.
Gauteng Premier David Makhura wished those injured in the bridge collapse a speedy recovery.
He said the MEC for Roads and Transport, Ismail Vadi, was on the scene assessing the damage.
“Our thoughts and prayers are with those in hospital. I shudder to think what would have happened if this occurred during peak hour traffic,” said Vadi.
In October 2015, a pedestrian bridge in Grayston Drive, which was under construction and which was to link Alexandra to Sandton, collapsed, killing two people and injuring 19.
The Department of Labour has still not concluded its investigation saying it was experiencing difficulties in getting all the parties involved, together.