The earthquake that rocked Gauteng was the largest recorded since 2014 Photo MIT
Gauteng – In the hushed darkness of Sunday morning, the peaceful slumber of Gauteng’s residents was shattered by a force that surged through their homes. Like a symphony of unease, tremors measuring between 4.5 and 5.0 on the Richter scale reverberated through the walls, shaking the very foundations of their existence. With the recent Turkish earthquake still fresh in their minds, it was a harrowing experience.
South Africa experiences earthquakes relatively infrequently compared to other seismically active regions. In the past 10 years there have been nine earthquakes measuring 4.0 and above on the Richter scale. However, it wasn’t always like this, explained Professor Raymond Durrheim, South Africa Research Chair in Exploration, Earthquake & Mining Seismology.
“Here in Johannesburg and in the Gauteng region, these earthquakes are unusual but 30 or 40 years ago, in the late 1970s they were a regular event. We’d have a felt earthquake every week because in those days there was active mining just south of Johannesburg. South of the M2 in the Boksburg region. The East Rand Proprietary Mines at that stage was a very big and active mine. It was the deepest mine in the world, mining at depths of greater than three kilometres below the surface.”
Causes of the earthquake in Johannesburg
The Council of Geoscience is currently analysing detailed data to provide a more precise understanding of the recent earthquake’s specific cause. However, preliminary information suggests a connection to the decades of mining activities in the East Rand region.
“If you look at all the mine dumps that you see on the surface you can imagine all that rock would have come from deep underground. At one time there were very extensive excavations. Each excavation is not very high. Perhaps one or two metres high so they weren’t very tall excavations but with huge lateral extent. The Earth is still trying to close those voids and gradually as the rock creeks and cracks we have seismic [activity] happening below what we can feel all the time but every now and again there’s an earthquake that’s big enough that we can feel it.”
While this seismic activity may be related to mining that happened decades ago, there are those who are concerned that Zama Zamas are also to blame for the earthquake. However, Durrheim pointed out the illegal miners operate at shallow depths near the surface, and their activities are unlikely to cause significant earthquakes. While that may be the case, it does not mean what they are doing is safe.
“The Zama Zamas generally are working at shallow depth. They’re not working deep down and in fact these deep mines have been allowed to flood. Their activities are very risky because often they are chipping away at old pillars, they’re not putting in the support. They don’t have all the safety systems. That can lead to perhaps a road or a railway line [collapsing].”
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Aftershocks and preparedness
Aftershocks are common after an earthquake, with the largest aftershock typically being one magnitude unit smaller than the main shock. While aftershocks can be alarming, they are unlikely to cause significant damage. Still, it is important for one to be prepared and to know how to act during an earthquake.
“The general advice is … if you feel an earthquake don’t try to run outside. You’re more likely to be trampled in a stampede or fall down the stairs or be struck by falling masonry or shattering glass. What you need to do is first drop to the ground and then seek cover under your school desk or under a table or perhaps in a doorway. Then hold onto the leg of the table because the shaking could cause this to move and to protect you perhaps from objects falling from the ceiling or the collapse of a roof. Wait it out for those few seconds that will take and then cautiously get out.”
The recent earthquake in Johannesburg reminded residents of nature’s unpredictable force. South Africa experiences earthquakes infrequently, but past mining activities may be linked to seismic events. While concerns about illegal miners persist, their shallow operations are unlikely to cause significant earthquakes. Preparing for aftershocks and knowing earthquake safety measures are crucial for resilience.
In an engaging conversation with Julie Alli, Professor Raymond Durrheim delved into the connections between climate change, earthquakes, plate tectonics, the melting ice sheets, and sea level changes. Listen to that discussion here:
