12 January 2005

Cape safe from tsunamis

Should a tsunami ever hit the Mother City from the south, the harbour would be protected because of its geography, but should it come from the northwest, the Cape coast could see extremely high waves.

Robben Island might serve as a buffer, or else it might concentrate waves on a specific area depending on various circumstances and the direction of the wave, David Phelp, a coastal engineer at the CSIR said on Tuesday.

He said it was impossible to do a general forecast for the Cape Peninsula; these forecasts could only be done for specific areas.

But chances of a tsunami ever hitting the South African coast were zero, said Dr Andrzei Kijko on Tuesday.

Kijko, a seismologist at the Council for Geoscience, which specialises in risk analysis, said the South African coast simply did not comply with the various "requirements" for a tsunami.

"People can relax - it just cannot happen here," he said.

He said several factors had to be present to cause a tsunami such as the one that caused such total destruction in Southeast Asia.

Firstly, there has to be an extremely strong earthquake, registering at least seven on the Richter Scale, "to generate the energy necessary to move such a mass of water".

He said: "The sea bottom has to either lift or subside. In short, it has to be replaced suddenly in a vertical direction."

The coast should also have either a "V" or a "U" shape. The South African coast is straight.

The worst South Africa would experience after an earthquake on the sea bottom, would be a surge of water and a rising water level, which would be far removed from a tidal wave.

But South Africa did face one danger: The possibility of an earthquake in Ceres or Tulbagh.

"Indications are that a big quake could take place," he said.

The first recorded earthquake in South Africa was reportedly in 1620.


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