Earthquakes in South Africa – The Mail & Guardian

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Local residents and rescue volunteers take part in a search operation on February 7, 2023 in Albistan, Turkey. (Photo by Mehmet Kakamaz/Getty Images)

Earthquakes can be frightening – the stillness and calm that precedes a sudden, violent quake. Often, they can be devastating, as was the case in Turkey in February, when an earthquake of about 7.8 on the Richter scale killed more than 50,000 people.

By comparison, the earthquake that struck Johannesburg last Sunday had a magnitude of about 5.0, which would make it a medium-magnitude earthquake. It hit about 17 kilometers underground, which is relatively shallow.

The quake hit the East Rand, a traditional mining area. Mining areas where there are large underground excavations can create stresses that can cause earthquakes. This came according to the Earth Sciences Council, which is conducting studies to determine the cause of the earthquake that occurred last week.

“Some of South Africa’s gold and platinum mines are so deep that the great pressures around drilling operations outweigh the strength of the rock, which can suddenly explode,” expert Ray Durheim wrote in The Conversation in 2019.

“This can cause shaking strong enough to damage nearby fossils,” Durheim added.

He also said rock blasts posed a danger to miners and nearby communities. This can happen anywhere the mining is deep enough.

Historic mining in the East Rand is being investigated as a possible cause of the recent earthquake.

The KwaZulu-Natal region has significant seismic activity due to the presence of tectonic plates, which are the outer layers of the Earth’s crust broken into large pieces.

The Earth Sciences Council believes that Gauteng is more stable in terms of its tectonic activity than KwaZulu-Natal or even Cape Town, but this is not in stone. Last weekend’s earthquake could have been the result of tectonic activity elsewhere releasing pressure in Gauteng. It could also be that historical mining in the area led to a change in ground pressures or even that the tremor was caused by fluctuating water levels.

Both the Earth Science Council and Earthquakelist.org, a resource for earthquakes that occur around the planet, have cautioned that aftershocks should not be ruled out, although they think these are unlikely and possibly small if they occur.

Mining

Being a mining town, Johannesburg is no stranger to tremors, which is why many residents thought the tremor felt on Saturday might have been just one of them.

Durheim and colleagues analyzed an earthquake that occurred in Klerksdorp in 2005. The magnitude 5.3 quake killed two people and injured 58. The earthquake was felt in the nearby town of Stilfontein as well as in Johannesburg and a nearby mine in Klerksdorp.

The study found that “the magnitude 5.3 event and its aftershocks can be attributed to past mining.”

“This event resulted from renewed slippage on an existing major fault, with extensive mining activities in the area contributing most of the stress energy.

The possibility that these events could only be caused by natural forces is considered to be very small.”

A crucial finding noted in the paper is that the statistical analysis showed that there were higher chances of damaging seismic events in areas where gold mining was taking place. The study said these types of seismic events become more likely as mining continues and need to be monitored.

“Some buildings in gold mining areas are vulnerable to damage and even collapse during seismic events, which poses safety and financial risks.”

earthquake magnitude

The normal assumption is that the magnitude of an earthquake determines the damage it does. But this is not true. According to Durheim: “Earthquakes don’t kill people, they do. Buildings do.” Oftentimes, it’s infrastructure ill-equipped to handle earthquakes that topples and causes deaths.

It is not known that there are major earthquakes in Africa. There have only been four that have measured above 7.0, including a 7.3 event that struck Tanzania in 1910. Algeria and Morocco are high on the risk list, as are countries on the East African Rift.

An example of a medium-sized earthquake that caused widespread damage was the one that struck Morocco in 1960. It had a magnitude of 5.7 but killed about 13,000 people, making it the deadliest earthquake to strike Africa and one of the deadliest earthquakes globally in terms of lives. . Lost.

This ties in with the argument that infrastructure must be able to withstand earthquakes.

Durheim writes that disaster managers; emergency first responders; Planners, regional planners, architects and engineers all have key roles to play.

Forming and enforcing building regulations and training emergency services and the public on what to do in the event of an earthquake are two of the best ways to mitigate risks associated with earthquakes.

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