Why Durban felt the quake

Stephen Coan, The Witness

Durban - An earthquake in Durban? Blame it on the beach.

On Tuesday, Durbanites got a taste of the earthquake that registered 5.5 magnitude on the Richter scale at its epicentre in faraway Orkney in North West.

“It was noticed in Durban because the beach sand tends to amplify the ground motion,” said Michelle Grobbelaar, Council for Geosciences Seismology Unit manager, based in Pretoria.

“In Mexico City in 1985, there was an earthquake quite far away but it destroyed parts of the city because it was built on an old lake bed.”

Grobbelaar said the event also felt more prolonged on the coast because this was at the periphery of the earthquake, likening it to an extended wave motion. “At the site of the event you would feel it all in one go. The further away the more you feel.”

Grobbelaar said the earthquake was a “big event” for South Africa and recalled the Ceres, Western Cape, earthquake of 1969 which was also felt across the country.

“It seems the South African geology propagates the movement a lot further.”

Grobbelaar said although the epicentre of Tuesday's earthquake was located in a mining region, it’s “difficult to determine what caused it. We still don’t fully understand the phenomena”.