Is the next earthquake due?

Recent earthquakes that caused major destruction and loss of life in other parts of the world have raised the questions of just how prepared South Africa is for such a natural disaster, and how big the risk is of it occurring. The questions are of particular concern to residents of Cape Town’s Milnerton, Table View and Melkbosstrand suburbs, which straddle a major fault line known as the Milnerton Fault.

However, the rest of South Africa seems equally at risk of experiencing a fairly big earthquake event. Experts say large areas of the African continent are in an unstable, tectonically active state. The most immediate threat, nonetheless, seems to be centred in Cape Town.

Predictions of an imminent 'big one' became more common after a minor earthquake measuring 3.1 on the Richter scale shook these parts in 2003.

The day after the 1809 earthquake, people travelled from Cape Town to stare in awe at geysers of muddy water spurting upwards from schisms that had appeared in the earth. The epicentre was in the vicinity of Rietvlei, and the farm house at Jan Biesjes Kraal – which stood more or less where the Paddocks Shopping Centre is situated in current-day Milnerton Ridge – was flattened.

The Milnerton Fault runs 8 kilometres offshore near Koeberg nuclear power station, through Table View and Milnerton, and on to the Cape Flats and part of False Bay.
Further northeast of Cape Town, a major earthquake in 1969 destroyed many buildings in the towns of Tulbagh and Ceres.

Recent seismic activity in the area has caused geological experts to warn that the Milnerton Fault has resumed activity, a warning taken seriously by the municipality of Cape Town. This emerged when some time ago the city insisted that a new 20-storey apartment building in Table View be built according to stringent “earthquake-resistant” specifications.

Charlotte Powell, Public Awareness & Preparedness manager in the Cape Town City Disaster Risk Management Centre, says that in view of scientific evidence, there is a low to moderate probability of an earthquake occurring in Cape Town. But the city’s disaster management priorities are geared more towards frequently occurring hazards such as fires and floods.

However, as part of the city’s preparations for the 2010 Fifa Soccer World Cup, the city has acquired additional personnel, specialised equipment, and vehicles, and is providing extensive training to deal with emergencies such as collapsed buildings.

“We are in the process of establishing an Urban Search and Rescue Team as part of our all-inclusive planning and preparations for 2010. This legacy of planning and preparation for 2010 will stand us in good stead to respond to any other major incidents, including earthquakes.”

Neither is Eskom not ignoring the threat. While the existing nuclear power station is already built to withstand earthquakes, a draft scoping report for Eskom's planned second nuclear plant says a serious earthquake affecting Koeberg is “improbable” while it being hit by a tsunami is “possible”. Nonetheless, the report says a new power station would have to be able to withstand short periods of tectonic (earthquake) activity.

Scientists say the earth’s crust is unstable and stressed to a critical limit in southeastern Africa. What is called the "African super swell", a mass of warm volcanic rock, is rising under much of southeastern Africa, producing a particular effect that is helping to pull the crust apart, particularly in the higher mountainous areas.

Exacerbating risks of earthquakes are various human activities such as, for example, the building of massive dams or water reservoirs in high-lying, mountainous regions such as that of the Lesotho Highlands Water Project. Underground mining activity, particularly the ultra-deep gold mining operations in South Africa, also pose a risk of intensifying the threat of earthquakes.

Within days of the reservoir behind the Katse Dam in the Lesotho highlands being filled in late 1995, a series of tremors were felt in the area, with one in January 1996 recording 3.1 on the Richter scale.

In South Africa, the Seismology Unit of the Council for Geoscience (CGS) is responsible for monitoring regional seismicity of southern Africa through the operation and maintenance of the South African National Seismograph Network (SANSN), and various other seismological stations in eastern and southern Africa.

These stations provide information on the occurrence of earthquakes and enable assessment of the seismic hazard in the subcontinent, such information being supplied to engineering houses, insurance companies and state organisations, including the South African National Disaster Management centre (SANDMC). The latter again relays information down to the provincial and municipal disaster management centres and other agencies.

While modern instrumental data offers the best and most complete information about earthquakes, it must be supplemented by historical and geological evidence as seismometers have not been around long enough to provide a basis for unqualified geological conclusions, says the CGS.

The CGS has a record of events in South Africa dating back to an event in 1620, recorded by the crew of a ship anchored off Robben Island.
In 1811, the Milnerton Fault gave Cape Town residents another fright of between 5 and 5.6 on the Richter scale.

In 1912, many farm buildings were destroyed in a quake measuring 6, with its epicentre at Koffiefontein in the Free State.

Thereafter, various shocks registering between 5 and 6.3 hit the De Doorns-Worcester-Ceres area (1963), the Tulbagh and Ceres area (1969), Welkom in the Free State where buildings were damaged and block of flats collapsed (1976), and Carletonville west of Johannesburg (1992).

There has been a multitude of smaller quakes in between.

In February 2006, a powerful earthquake measuring 7.5 hit Mozambique and was felt as far as Durban and Harare.

One of the most recent seismic events was a light tremor of 1.6 on the local Richter scale recorded at Springbok in the Northern Cape on 25 May this year. It caused some consternation in Springbok, but no damage.

After the first seismographs were introduced in South Africa in 1910, a modern national network of seismological stations has been developed since 1971 and is operated by the Seismology Unit. Since 1988, several seismological stations have been upgraded, with the current network comprising 29 seismological stations, of which 23 are digital.

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Comments (5)

• |2010-03-11 10:20:42 Nicole  - earthquake
  How would we know when this will happen? What is the most recent news on the Milnerton Fault? Do we start packing our bags and moving?
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• |2010-03-11 10:39:12 Anonymous
  Hi Nicole,
  The short answer is that you won't know when this will happen. The quake itself is not predictable, but what is, is that it is usually followed by a tsunami. It is 200 years since the last activity from the Milnerton fault so on probability it could happen almost any time. But then, it could also be another 200 years before it happens. There is no reason to start packing and moving because it can also happen elsewhere. What is important is that one keep yourself educated on what to do if it should happen. To be prepared for if or when it does happen – like we teach our children to swim, not just for fun but as a life skill they might some day need for survival.
  Piet Coetzer, Editor
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• |2010-04-16 08:47:42 Ian du Toit
  Hi Piet
  
  What is the wright and wrong in case of, and after a earthquake ?
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• |2010-03-23 18:16:01 H.J. FOUCHE  - Aard beweging
  Ek skryf in Afrikaans aangesien ek my beter kan uitdruk.
  Daar is min mense wat dit weet. Gedurende die begin van 1960 was ek in die Lugmag en gestastioneer te Langebaanweg. Dit was in die oggend toe dit gebeur het. Ek en een van my kollegas het ontbyt in die mensaie geniet. Skielik hoor ons twee n ontploffing en my opmerking was dat dit 'BOMB DUMP' wat ontplof het. My kollega sê vir my nee dit klink nie so nie. Net daarna hoor ons n baie snaakse klank wat aankom. Meteens kyk ons na die vensters en sien hoe dit beweeg en dat die vloer soos golwe onder ons voete beweeg. Dit het vir n kort stonde so geduur.
  Ek het in Maraisburg naby Johannesburg groot geword en weet van die aardskuddings daar en dit is nie dieselfde wat ek en my kollega daardie oggend beleef het.
  Ons is bekend met personeel wie getroud was en wie in een van die huise gebly het.Die het dit ook ondervind. Hulle het die agtermiddag aan ons meegedeel dat hulle Budgie se hokkie om geval het.
  Die spesialiste kan maar gaan n...
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• |2010-07-25 09:04:27 piet blackwolf  - Milnerton aardbewings belt
  Ek weet van dalk 'n moontlike probleem met Koeberg dat dit kan ontplof omrede van die swak bestuur,dit was voorspel gewees amper 'n 100jaar gelede.Maar die Milnerton belt is 'n verrassing en maak die Kaap nou nog meer intersanter om in te bly,altwee kan die Kaap verwoes.
  Ek was op die rolskaatsbaan gewees in Parow 1969 toe die aarbewing ons hier getref het van Tulbagh se kant af.Dit was 100km vêr weg!!! Ek wil nie weet hoe gaan dit wees as die aardbewing reg onder ons gaan wees nie,daar sal nie baie staande bly nie.Ons het ook 2 oeseane aan weerskante.As daardie skudding vêr genoeg die see ingaan kan dit'n baie groot brander veroorsaak wat binne ure oor die Kaap kan kom.
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