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| Libanon Mine of Sibanye near Westonaria, South Africa South East of Johannesburg in the Earthquake zone |
At 12h44: Wow! We just had a tremor run though Roodepoort (near Johannesburg, Gauteng) at approximately 12h25! Seems that this isn't the first time that a tremors or earthquakes have struck. There have been a few in the past as well, this one was felt by some of my friends in Pretoria (South) as well and likely originated from an old mine shaft that collapsed, (maybe the Brixton one again, not sure!).
Updates to follow!
At 12h55, alright from the people coming in on this post (from my blog stats), it seems people felt this in:
Santon
Johannesburg
Pretoria
Centurion
Cape Town
East London
Germiston
Midrand
Durban
Benoni
Klerksdorp
Krugersdorp
Olifantsfontein
Berea
Randburg
Westville
Emalahleni
Boksburg
At 13h00: The reports are in!
Time of occurrence 12h22
Earthquake of 5.3 magnitude! (Amended to 5.5 by experts at a depth of 10 km)
Centered in Orkney, 120 km Southwest of Johannesburg! An area with many gold mines. At around 13h15 South African gold miners with head offices in Johannesburg and Sandton advised that they had felt the earthquake at their head offices but have so far received no reports of damage from their mines.
Earthquakes and deep level mining does not bode well and I hope that no mine workers will be injured.
Seismometers measure earthquakes according to the Richter magnitude scale, which quantifies the amount of energy released by an earthquake - more specifically total moment energy.
Measuring at 5.3; today’s earthquake can be described as ‘Moderate’.
It can cause damage to building with poor construction and everybody will feel
its tremors. On a global scale, approximately 500-1500 of these earthquakes occur per year. Only earthquakes that reach above 7 cause great damage to buildings and are classified as Major (around 7) and Great (above 8). Earthquakes of magnitude 8 release an equatable amount of energy to 6 million tons of TNT!
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| Earthquake hits central South Africa Google maps platform © Red marker: Earthquake origin at Orkney Blue maker: Roodepoort, Gauteng |
References:
Reuters Africa
3) International: USA Today
At 14h45: Can we expect aftershocks from this Earthquake event?
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| Seismogram |
After some research the short answer is: YES.
Magnitude 5 (M5) earthquakes can generate aftershocks minutes after the initial event that can last for days. These will be with in a 10 kilometre radius from the epicentre These follow a precise sequence and there may be 10 aftershocks of magnitude 4; 100 of magnitude 3; 1000 of magnitude 2 and so on, which by then would no longer be felt by people. Also most of the aftershocks occur hours after the initial event an soon dissipate, likely ceasing on the second day.
Aftershocks were felt mostly in Gauteng:
Reference: Aftershock Studies
At 16h00: Tectonic events and the Witwatersrand Basin
There is a large and complex formation of rocks around the Witwatersrand area. It has one of the largest gold reserves in the world as well as numerous other rock series such as quartzites and ironstones, collectively known as the Witwatersrand Supergroup.
In this area is the largest concentration of South African gold mines including some of the deepest, most of which are 120 kilometers from Orkney.
Mponeng: Near Carletonville and is 2.4-3.9 kilometers deep. It is the deepest gold mine in the world!
TauTona: Also near Carletonville, 1.85-3.45 kilometers deep. It is the second deepest gold mine in the world!
The geological area around the Witwatersrand Basin is prone to tectonic events due to underground movements and fault lines. Reference: The Witwatersrand Basin South Africa: Geological framework and mineralisation. 1995. Robb L. J. and Meyrs F. M. One Geogolical Reviews: 10. 67-94.
The Witwatersrand Basin had generated a tectonic earthquake and several mines in the vicinity could have been effected as well. Such as the Great Noligwa (1.5-2.6 km deep), Kopanang (2.1 km deep) and Moab Knotsong (2.6-6.3 km deep). See diagram for mines near Orkney below:
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| Witwatersrand Basin Mine Locations Source: Mineral Resource and Ore Reserve Report 2013, AngloGold Ashanti |
At 18h30: Are more earthquakes imminent? Should South Africa expect another earthquake in the future?
Yes, many factors indicate that this area might generate more earthquakes in the future due to tectonic plate movements. Therefore it becomes a question of WHEN and not IF.
The Witwatersrand Basin is likely susceptible to tectonic activities from the African Plate fault line, which extends through middle (more to the Eastern side) of South Africa and in the earthquake zone. The plate on the Eastern side (Somali African Plate) is moving away from the Western (Nubian African Plate) and will likely generate more earthquakes in the future. Please see the following map and blog post: World Maps of Fault Lines and East Africa: The Next Continent.
At 19h00: Earthquake awareness for Africa and What to do when a earthquake strikes!
Scientists have been calling for greater awareness of the occurrence of earthquakes in Africa due to the shifting plates. The Millerton fault in the Cape has the potential to generate magnitude 6 earthquake. The key to earthquake management is to be prepared and stay safe rather than earthquake prediction.
The key thing is when you are indoors and an earthquake strikes is to avoid being thrown or hit with falling objects. Therefore climbing under and holding onto your desk is the safest place indoors.
If you are outside then move away from buildings or walls and stay in the open. When an earthquake occurs while driving, move off the road and stop the car avoiding overpasses or other large objects that may fall over.
After the earthquake, check for fires and check that the phones are working. Be aware of stored objects in cupboards as they might fall out.
For more information on how to prepare for, what to do during and after an earthquake see the following websites:
How to Protect Yourself During an Earthquake
Be Prepared Before, During and After an Earthquake
Other references:
Cape Town Earthquakes: Review of the Historical Record by C. J. H. Hartnady
Scientists Call for Earthquake Awareness in Africa
On 6 August 2014 at 13h00: News about the chances of another earthquake have been aired.
Again it is a matter of when and not if. We can expect one of the same magnitude in the future due to the mining activities in the Orkney region that disrupts the geological statues of the Witwatersrand Basin and the African plate fault lines. ... Seems like my initial thought that mining was involved in some way was correct...
See News bulletins (the first with a video from a Geosciences expert):
Another earthquake of equal magnitude expected: expert
Quake triggered by mine activity - expert
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