Milnerton Fault a ’seismic hazard’ making earthquakes inevitable – expert, Newsline

Cape Town – The general consensus has been that a magnitude 6.2 earthquake that struck about 1 600km south-east of South Africa at the weekend, with subsequent tremors being felt in parts of Cape Town, is no cause for panic.

However, indicating that the future recurrence of strong earthquakes along the Milnerton Fault is a “major natural hazard in the Cape Town area”, CH Hartnady wrote in Cape Town Earthquakes: Review of the historical record: ’’Strong earthquakes of magnitude 6 or greater will inevitably recur along the Milnerton Fault.

“It is therefore important to raise public awareness of the seismic hazard issue, both at the grass-roots community level, and at the higher, decision-taking level of metropolitan councillors and civic planners.”

He based this on the two largest historical earthquakes – on 4 December, 1809 and 2 June, 1811 – that occurred in the Western Cape before the Ceres-Tulbagh earthquake of 29 September, 1969. Detailed eyewitness descriptions established that the common focus of these strong (magnitude 6) events was only 20-30 km from the modern city centre, he wrote.

“In the Western Cape, the need is not for the sophisticated high technology, such as prediction research or early-warning systems, adopted in places such as California, Mexico, or Japan, where the seismic hazard is both more overt and much greater. What is required is better community preparedness to live with earthquakes so that the need to ‘predict’ is reduced.

’’The reactor at the Koeberg nuclear power station is built upon a seismic raft designed – on the basis of a mid-1970s hazard study – to withstand a magnitude 7 earthquake at a focal distance of about 10km.

“How many schools and other key facilities close to the trace of the Milnerton Fault are designed to these rigorous standards? And, if none, why not?

”As its omission from the draft 1997 MSDF document shows, no formalised contingency planning currently exists for a repeat earthquake disaster of the same magnitude as 1809-1811.“