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Joburg earthquake measuring 3.6 magnitude 'linked to a century of gold mining'

30 July 2021 1:43 PM
Tags:
Earthquake
Johannesburg
Gold mining
Witwatersrand Basin

Mandy Wiener speaks to Prof Ray Durrheim Research Chair in Exploration, Earthquake & Mining Seismology at Wits.
  • The earthquake measured at a magnitude of 3.5 on the local magnitude scale
  • Expert Prof Durrheim explains how a century of gold mining around the Witwatersrand Basin has left voids which under pressure from rock above can cause such tremors and quakes

The seismic activity occurred around 6.30 am in Johannesburg notably around the Benoni and Boksburg area.

Was it a tremor or an earthquake - or Tatjana Schoenmaker taking a gold medal at the Tokyo Olympics jokes Mandy?

Well I suppose there is a connection as she took gold, and the earthquake is connected to the gold mining that has happened in the East Rand here in South Africa for the last century.

Professor Ray Durrheim, South African Research Chair in Exploration, Earthquake & Mining Seismology - Wits University

Extensive mining over the last century around the Witwatersrand Basin has created voids he explains.

With time gravity causes the weight of rock above these voids, and it slowly creaks, and cracks, and closes, and so you get ruptures forming every year, and every now and then it slips and is felt.

Professor Ray Durrheim, South African Research Chair in Exploration, Earthquake & Mining Seismology - Wits University

Some earthquakes however can be related to natural phenomena with the movement of tectonic plates.

Whether it is a quake or a tremor is really a matter of semantics with the word tremor often use for something a bit smaller, but the word earthquake is the generic term for anything that is felt when the earth shakes.

Professor Ray Durrheim, South African Research Chair in Exploration, Earthquake & Mining Seismology - Wits University

He notes that there are several different scales used to measure.

The Richter Scale strictly speaking, only applies to California. Here we use something similar to the Richter Scale but adapted it to your region taking into account the proximaty to the earth - and that is called a local magnitude scale.

Professor Ray Durrheim, South African Research Chair in Exploration, Earthquake & Mining Seismology - Wits University

He says that is what has been reported in this case by the South Africa Council for Geoscience as that of 3.5.

However, the United States Geological Survey also located the event and use a global network of seismographs called the Body Weight Magnitude Scale.

While that has a slightly different magnitude they will all be reconciled in the end.

Professor Ray Durrheim, South African Research Chair in Exploration, Earthquake & Mining Seismology - Wits University



30 July 2021 1:43 PM
Tags:
Earthquake
Johannesburg
Gold mining
Witwatersrand Basin

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